3176 DIESEL TRUCK ENGINE Caterpillar

5.0 Electronic Subsystem Functional Tests

Usage:

Electronic Subsystem Functional Tests

These tests are designed to establish whether a component and related parts are working correctly and if not, to pinpoint the faulty component.

These tests may also be used for basic health checks, to determine if problems exist, or as a guide to check for intermittent problems.

P-501: Inspecting Electrical Connectors

Many of the Operational Procedures and Diagnostic Code Procedures in this troubleshooting guide will direct you to check a specific electrical connector.

Use the following steps to help determine if the connector is the cause of the problem. If a problem is found in the electrical connector, repair the connector and continue the test procedure.

1. Check "DT" & "DRC" connector locking, and "HD" connector lock ring.

Make sure that the connector is properly locked (clicked) together and that the two halves can't be pulled apart.

2. Perform 10 pound pull test on each pin/wire.

Each pin and connector should easily withstand 10 pounds of pull, and remain in the connector body. This test checks whether the wire was properly crimped in the pin, and whether the pin was properly inserted into the connector. The "DT" connectors use an orange wedge to lock the pins in place. Check to see that the orange wedge is not missing and installed properly on the "DT" connectors. Repair as needed.

NOTE: Pins should ALWAYS be crimped onto the wires; NEVER soldered. Use the Deutsch Crimp Tool (Cat P/N 1U5804).

3. INSPECT CONNECTORS. Verify that pins and sockets are not corroded or damaged. Verify proper alignment and location of pins in the connector.

4. CHECK INDIVIDUAL PIN AND SOCKET CONNECTIONS. This is especially important for intermittent problems. Using a new pin, insert the pin into each socket one at a time to check for a good grip on the pin by the socket. Repeat for each pin on the mating side of the connector, using a new socket for the test.

P-510: Electrical Power Supply To The 3176 ECM Test

System Operation

The 3176 ECM receives electrical power (battery voltage) through wiring supplied by the vehicle manufacturer. In typical applications, 3176 receives power whenever the key is turned on.

Some vehicles may be equipped with an engine protection shutdown system or an idle timer shutdown system (external to 3176) that interrupts electrical power to the ECM to shutdown the engine. Some of these will not supply power to 3176 until the engine is cranked, until oil pressure comes up to acceptable limits, or until an override button is pressed. Keep in mind that these devices may be the cause of intermittent power to the ECM.

This procedure tests whether proper voltage is being supplied by vehicle wiring.

For intermittent problems that could be caused by vehicle wiring (such as intermittent shutdowns) temporarily bypassing the vehicle wiring may be an effective means of determining the root cause. If symptoms vanish with the wiring bypassed, vehicle wiring was the cause. A means of bypassing vehicle wiring is explained in step 4 of the functional test.

Schematic

Diagnostic Codes

Functional Test

Illustration 3

P-511: Throttle Position Circuit Test And Calibration

System Operation

The throttle position sensor is used to provide a throttle signal to the ECM. Sensor output is a constant frequency signal with a pulse width that varies with throttle position. This output signal is referred to as either "Duty Cycle" or a "Pulse Width Modulated" (PWM) signal and is expressed as a percentage between 0 and 100%.

The Throttle Position Sensor may be one of two types. The "remote mounted" sensor is slightly smaller than a soda can and is connected to the throttle pedal by an OEM supplied linkage. This sensor requires adjustment for proper operation. The "pedal mounted" sensor is attached directly to the pedal assembly and requires no adjustment. Both sensors provide the same type signal to the ECM. Note: the pedal mounted sensor can be replaced separately from the pedal assembly. An incorrectly calibrated pedal mounted throttle position sensor assembly cannot be adjusted- the pedal assembly must be replaced.

When properly adjusted, the remote mounted TPS will produce a "Duty Cycle" of 15 to 20% at low idle and 80 to 85% at full throttle. The pedal mounted sensor will produce a "Duty Cycle" of 10 to 22% at low idle and 75 to 90% at full throttle. The percent duty cycle is translated in the ECM into throttle position of 3 to 100%.

Schematic

Diagnostic Codes

Functional Test

Example 3176: ECAP "Display Status Screen"

Illustration 1

The "Throttle Position" should read 3% with the throttle pedal released and progressively increase to 100% when the throttle pedal is fully depressed.

3176: ECAP "Duty Cycle Screen"

Illustration 2

* For the remote mounted sensor the DUTY CYCLE should be between 15 and 20% at the low idle stop and increase to between 80 and 85% at the high idle stop.

* For the pedal mounted sensor the DUTY CYCLE should be between 10 and 22% with the pedal released and increase to between 75 and 90% with the pedal fully depressed.

Illustration 3 - Installation/Replacement Of A Pedal Mounted Throttle Position Sensor Into The Throttle Pedal.

Throttle Position Sensor Calibration And Adjustment

NOTE: Only the remote mounted throttle position sensor can be adjusted or calibrated.

Correct Low Idle Position Adjustment

Illustration 4

Correct High Idle Position Adjustment

Illustration 5

3176: ECAP "Duty Cycle Screen"

Illustration 6

* For the remote mounted sensor the DUTY CYCLE should be between 15 and 20% at the low idle stop and increase to between 80 and 85% at the high idle stop.

* For the pedal mounted sensor the DUTY CYCLE should be between 10 and 22% with the pedal released and increase to between 75 and 90% with the pedal fully depressed.

P-512: 3176 Diagnostic/Warning Lamp Circuit Test

System Operation

Diagnostic Lamp

The Diagnostic Lamp is used to indicate the existence of a diagnostic code, to indicate "driver alert" status of the Idle Shutdown Timer, and may be used to read Diagnostic Codes. While the engine is operating, it will go ON for a minimum of five seconds any time a fault condition exists. It will continue to flash on for five seconds, and then blink off, flash on for five seconds, etc., as long as the fault condition exists.

On power up (key ON, Engine OFF), the lamp comes on for five to ten seconds, then go out for five seconds. After this time, active diagnostic codes will be flashed out.

Active faults may be flashed out at any time by turning the cruise On/Off switch to Off, and holding the Set/Resume switch in the Resume position until the lamp begins to flash, then releasing it.

Warning Lamp

The Warning Lamp is used to indicate the existence of a Caterpillar Engine Protection detected problem. The lamp is for Caterpillar Engine Protection, and used only when the Customer Parameter for Engine Protection is set to any mode other than "OFF".

The Warning Lamp will not come on with the key ON, engine OFF like the Diagnostic Lamp described above. The Warning Lamp should come on for a minimum of two seconds following engine start. If the oil pressure is insufficient the Warning Lamp will stay on until the oil pressure reaches an acceptable pressure. The Coolant Temperature and Coolant Level Sensors will not affect the Warning Lamp for the first 30 seconds following engine start up.

One terminal of both lamps is connected to battery voltage through a 10 Amp "Vehicle Fuse" whenever the key switch is ON. The other terminal is connected to the ECM at P7/J7 pin 29 (Diagnostic Lamp) or pin 12 (Warning Lamp) to turn the lamp ON. Pin 29 or 12 will be at battery voltage when the lamp is OFF, and less than 2 volts when the lamp is ON.

Warning Lamp And Engine Protection Modes

If the Customer Parameter for Engine Protection is set to "OFF", the Warning Lamp should not operate, and is unnecessary.

If the Customer Parameter for Engine Protection is set to "Warning", the Lamp will come on Solid (continuously ON) when a "Warning" condition exists.

If the Customer Parameter for Engine Protection is set to "Derate", the lamp will first go through the "Warning" mode just described, and if conditions persist, go to "Derate" with a FLASHING Warning Lamp.

If the Customer Parameter for Engine Protection is set to "Shutdown" the Warning Lamp will continue to FLASH following the "Derate" mode described above.

Schematic

Functional Test

P-513: Vehicle Speed Circuit Test And Calibration/Adjustment

System Operation

The vehicle speed circuit consists of the vehicle speed sensor, the vehicle speed buffer, and associated wiring. The sensor is a standard magnetic pickup and is supplied by the truck manufacturer. It senses movement of the teeth on the output shaft of the transmission. The buffer (Caterpillar supplied) takes the signal from the sensor, conditions it, and sends it to both the ECM and possibly the vehicle speedometer.

One of two types of Caterpillar speed buffers may have been installed. The 3E0020 is a newer/improved version of the 7T6398 and is a direct pin-for-pin replacement. Either buffer should be grounded at the same point as the ECM (cylinder head ground stud) through the -Battery (pin 2 of P7) to minimize "electrical noise" in the ground circuit.

The buffer is supplied with battery voltage through P14/J14 pin A. Ground is supplied through P14/J14 pin B. The buffer has outputs for both the ECM and the vehicle speedometer. The output to the ECM is a series of 5 volt pulses at J14/P14 pin D, whose frequency varies directly with the speed of the vehicle. The 3E0020 buffer has two outputs to the speedometer, one at pin C and one at pin E. Output at each one is a series of -10 volt to +10 volt pulses. The two outputs oppose one another; when pin C is at +10 volts, pin E is at -10 volts, and vice versa. The 7T6398 buffer has one output to the speedometer at pin C. The output is -2.5 to +2.5 volt pulses. Pin E is not used on the 7T6398 buffer.

NOTE: For speedometers requiring two signal input lines, the 3E0020 buffer should be used if the speedometer signal is fed from the Vehicle Speed Buffer.

NOTE: The vehicle speed circuit may vary dramatically from that shown here. Consult the Vehicle wiring diagram for more details.

Schematic 1: Vehicle Speed Circuit Using One Sensor - 3E0020 Buffer ONLY

Schematic 2: Vehicle Speed Circuit Using One Sensor - 7T6398 Buffer ONLY

Schematic 3: Vehicle Speed Circuit Using Two Separate Sensors - EITHER BUFFER

Schematic 4: Vehicle Speed Circuit Using Dual Winding Sensor - EITHER BUFFER

Diagnostic Codes

Functional Test

Example 3176: ECAP "Display Status Screen"

Example ECAP Screen of Vehicle Speed

Vehicle Speed Calibration And Adjustment

P-514: Cruise Control And PTO Switch Circuit Test

System Operation

The 3176 cruise control operates similar to automotive cruise controls. PTO operates similar to cruise, only it governs engine speed with the vehicle stationary, or at low vehicle speeds. The following five switch inputs affect cruise or PTO.

1. Cruise On/Off - This switch must be On for cruise or PTO to be activated.

2. Set/Accel or Decel - With the cruise On/Off switch On, momentarily pressing this switch will activate cruise, and will tell the cruise or PTO to try to maintain the current speed. Holding this switch On will cause cruise or PTO to slowly accelerate (Set/Accel) or decelerate (Set/Decel) this set point. Bumping the switch will accelerate (Set/Accel) or decelerate (Set/Decel) the set point at one mph (or 20 rpm in PTO mode).

3. Resume/Decel or Accel - With the cruise On/Off switch On, momentarily pressing this switch will activate cruise, and will tell the cruise or PTO to resume with the set point used when cruise was last disabled. Holding this switch On will cause cruise or PTO to slowly decelerate (Resume/Decel) or accelerate (Resume/Accel) this set point. Bumping the switch will decelerate (Resume/Decel) or accelerate (Resume/Accel) the set point at one mph (or 20 rpm in PTO mode).

4. Clutch - Depressing the clutch pedal will cause the cruise or PTO to deactivate.

5. Brake - Depressing the brake pedal will cause the cruise or PTO to deactivate.

NOTE: All of these switches are supplied by the vehicle OEM. To troubleshoot the Cruise ON/OFF, Set, or Resume switches, use this procedure. To troubleshoot the Clutch or Brake Switches, use P-515: Service Brake And Clutch Switch Circuit Tests.

The voltage at each of the inputs to the ECM should be 5.0 ± 0.5 volts DC with the switch OFF, and less than 0.5 volts DC with the switch ON.

Schematic

Functional Test

Example ECAP Screen of Cruise Control/PTO Switch Status

Illustration 1

Table A

Table B

P-515: Service Brake And Clutch Switch Circuit Test

System Operation

The Brake and Clutch switches are used in cruise control and PTO mode to discontinue cruise or PTO operation. The switches may also be used to override the Idle Shutdown Timer.

The brake and clutch switches are normally closed with the pedals released. Depressing either the clutch or the brake will open the individual circuits. Both switches are OEM supplied. The brake switch is typically a pressure switch. The clutch switch is typically a limit switch mounted near the pedal and is usually adjustable.

The brake signal goes to the Vehicle Connector through P7 pin 30. The clutch signal goes to the Vehicle Connector through P7 pin 31. Voltage at pins 30 or 31 to ground should be 5.0 ± 0.5 volts with the switch open, and less than 0.5 volts with the switch closed.

Schematic

Functional Test

Example ECAP Screen of Service Brake and Clutch Switch Status

Table C

Table D

P-516: Parking Brake Switch Circuit Test

System Operation

The Parking Brake switch is used only for the Idle Shutdown Timer fuction. The idle shutdown timer will only be activated when the parking brake is on.

The parking brake switch is supplied by the OEM. It should be normally closed (with brake applied, and no air pressure to the parking brake) and connected to ground. Releasing the brake should open the circuit. The idle shutdown timer will not operate unless the switch is installed to connect the parking brake input to ground (P7 pin 2).

The signal goes to the ECM through the Vehicle Connector (P7/J7), pin 11 to the ECM. Voltage at pin 11 should be 5.0 ± 0.5 volts with the switch open (parking brake released) and less than 0.5 volts with the switch closed (parking brake applied).

Schematic

Functional Test

Example ECAP Screen of Parking Brake Switch Status

Table E

Table F

P-517: Idle Shutdown Timer Test

System Operation

The idle shutdown timer is a feature which helps improve fuel consumption by limiting idling time. The timer may be programmed to shut down the idling engine after a period of time. This "shutdown time" is a customer specified parameter, and may be programmed for any period from 3 to 60 minutes. Programming the time to zero disables the idle shutdown timer.

The timer is activated when the parking brake is set, vehicle speed is zero, and the engine is not under load. Ninety seconds before the programmed time is reached, the diagnostic lamp will begin to flash rapidly. If the driver moves the clutch pedal or brake pedal during this 90 second period, the timer will be overriden until it is reset. A diagnostic code 71-00 Override Of Idle Shutdown Timer (01) will be set when the driver overrides the timer using the clutch or brake.

If the timer is activated and allowed to shutdown the engine, then a code 71-01 Idle Shutdown Timed Out (47) will be set. Code 71-01 merely records the event and does not indicate a fault in the 3176 system.

NOTE: If any of the following diagnostic codes are Active, the idle shutdown timer Will Not Operate:

84-08 Vehicle Speed Signal Out Of Range (36), Parking Brake Switch Fault (57) - NOTE: this code was eliminated for OCT91 and newer Personality Modules.

Diagnostic Codes

Functional Test

Example ECAP Screen of Idle Shutdown Status

P-518: Coolant Level Circuit Test

System Operation

The coolant level sensor is a vehicle OEM purchased and installed component. The sensor is the only optional sensor for Caterpillar Engine Protection equipped engines, selectable through a Customer Programmable Parameter (protected by Customer Passwords). Do not confuse an OEM installed Coolant Level Sensor that is independent (not used by/for the 3176 ECM) of Caterpillar Engine Protection with one used for Caterpillar Engine Protection.

Caterpillar currently specifies the vehicle OEM use only the Robertshaw Controls Co. RS-805B (85927-C1) sensor.

The sensor operates as a coolant loss sensor indicating the presence/absence of coolant at the sensor probe. The sensor is powered from the ECM through the 40-Pin Vehicle connector J7/P7, pin 18 (+5V). Note that this supply is shared by the Oil Pressure, Coolant Temperature, and Inlet Air Temperature sensors. The sensor signal wires are connected to the Vehicle Connector J7/P7 at pins 19 (Cool Level Low) and 39 (Cool Level Normal). The Sensor Common wire is connected to the 40-Pin Vehicle Connector through pin 2 (- Battery). The sensor pin out is:

Pin A = Cool Level LowPin B = Sensor CommonPin C = + 5VPin D = Cool Level Normal;

Cool Level Low has a nominal output of 0 volts DC with coolant present, and Cool Level Normal has a nominal output of +5 V DC with coolant present. The two outputs are complimentary, if coolant were not present at the sensor probe the Cool Level Low output would be +5 V DC, and the Cool Level Normal output would be 0 V DC.

NOTE: If Caterpillar Engine Protection is programmed through the Customer Programmable Parameter for Engine Protection in the OFF mode, or the Coolant Level Sensor is programmed to the Disable mode, the coolant level sensor is ignored by the ECM. Conversely, if both parameters are set (Engine Protection at either Warning, Derate, or Shutdown, Coolant Level at Enable), then a sensor must be installed or a diagnostic code will be logged.

NOTE: If the Sensor is installed, whether the ECM is programmed to read the Coolant Level Sensor signals or not (enabled/disabled), the Sensor or its' Harness may still affect the + 5V Sensor Supply. Therefore it must be considered in the troubleshooting procedure.

Schematic

Diagnostic Codes

Functional Test

Cutaway view of recovery or overflow tank.

Example 3176: ECAP "Display Status Screen"

NOTE: If the screen shows Coolant Level as "NOT INSTALLED", then the engine is not equipped for Caterpillar Engine Protection.

Example 3176: ECAP "Display Status Screen"

NOTE: If the screen shows Coolant Level as "NOT INSTALLED", then the engine is not equipped for Caterpillar Engine Protection.

Cutaway view of container with sensor probe immersed in water or engine coolant.

P-519: Retarder Enable Signal Test

System Operation

The Retarder Enable signal is provided by the ECM to indicate that conditions are acceptable for an engine retarder to operate. Operation of the retarder is inhibited during undesirable engine operating conditions (such as while the engine is being fueled).

With the cruise control On/Off switch in the Off position, the retarder is enabled under the following conditions:

Engine rpm is greater than 1000 rpm and Drivers foot is off the throttle pedal and clutch pedal.

With the cruise control On/Off switch On, the operation of the retarder is also controlled through the customer parameter "Engine Retarder Mode". Programming the parameter to "Coast" allows retarding with the service brakes applied, but allows the engine to coast with no retarding after they are released. Programming the parameter to "Latch" allows retarding with the service brakes applied and keeps the retarder latched On after the service brakes are released (until rpm drops below 950 rpm or the driver presses the throttle or clutch pedal).

The retarder enable signal should be 12 volts DC (nominal) to indicate that the retarder is enabled and 0 volts DC (nominal) to indicate that it is disabled. The remainder of the engine retarder circuit is supplied by the OEM. In typical applications the retarder enable signal will operate a relay, which switches battery power to energize the retarder solenoids. An "Engine Brake On" switch will be wired in series with the relay and must be On before the brake will operate.

NOTE: The ECM retarder enable signal usually routes into the vehicle cab. In the cab it will connect to the Engine Brake ON/OFF switch and Engine Brake Relay. The contact side of the Engine Brake Relay may also route through the Engine Brake ON/OFF switch, then through an Engine Brake Selector Switch, and eventually return to the engine to connect to the Engine Brake Solenoids. Consult the OEM wiring diagram for further information.

Schematic

Functional Test

P-520: J1922 Powertrain Data Link Test

System Operation

SAE J1922 Powertrain Data Link

J1922 Powertrain Data Link is an option designed to offer traction control of drive wheels to prevent wheel spin, and to provide smoother transmission gear shifts. This is accomplished by a momentary reduction of engine speed and/or torque, triggered by a signal from an off-engine control module (not part of Caterpillar's engine control system) for the traction control or transmission. Powertrain Data Link sensors, off-engine control modules, and wiring are installed by the vehicle OEM, and questions relating to the hardware, software, and installation should be referred to the OEM. J1922 refers to the SAE standard for Powertrain Data Link Communications.

NOTE: In the discussion that follows, Vehicle OEM Components (sensors, control modules, etc.) are identified as "Vehicle", and should not be confused with Caterpillar supplied components.

Either or both of the features may be installed, and are obtained by installing the required Vehicle sensors and control modules, and by replacing the standard Engine Personality Module with one containing the required software and hardware.

Loss of traction is determined by Vehicle sensors mounted near the wheels, and transmission shift points by a Vehicle sensor in the transmission. The sensor activates the Powertrain Data Link Vehicle control module which then communicates with the Engine ECM. The Engine ECM responds by momentarily limiting engine speed, torque, or both.

The presence of an active J1922 Powertrain Data Link circuit can be determined by observing ECAP status screen 1. The display "Powertrain Stat" will show "Installed" if the proper personality module is installed on the ECM, and there is no action being requested at that time by any of the control modules on the data link. If the personality module does not contain the proper software and hardware the status display will show "Not Installed".

If action is being requested by one of the Vehicle Control Modules the display will show the requesting control "Tractn Ctrl" or "Trans Ctrl" or a combination of the two: "Tractn & Trans". "Powertrain Control" is also displayed in the upper right hand corner of the display status screen. This space is pre-empted by the display "Low Oil Pressure", when a condition of low oil pressure exists.

Failures of a Vehicle Sensor or wiring to the Vehicle Control Module will not trigger a code 249-11, nor will failure of a Vehicle Control Module.

The data consists of a series of 5 volt pulses. Data reaches the ECM through the vehicle connector J7/P7 pin 9 (J1922 Data Link +) and pin 20 (J1922 Data Link -), then through J4/P4 pin 38 (J1922 Data Link +) and pin 29 (J1922 Data Link -).

NOTE: The data link wires are twisted to reduce electromagnetic interference. If a section of wiring must be replaced, the new wires should also be twisted together. Use care to maintain original wire polarity when installing pins and sockets into connectors.

Diagnostic Codes

Functional Test

3176 : ECAP "Display Status" Screen

P-521: ECM/Personality Module Test

System Operation

The Electronic Control Module (ECM) is the computer which controls the 3176 Diesel Truck Engine. The Personality Module contains the software which controls how the computer (ECM) behaves. The two must be used together - neither can do anything by itself.

The Personality Module Consists Of:

* All of the software, or instructions for the ECM to do its job. Because of this, updating the Personality Module to a different version may cause some engine functions to behave in a different manner. Contact your Caterpillar dealer if this occurs.* Performance Maps, which define fuel rate, timing, ect. for various operating conditions to achieve optimum performance while meeting emissions requirements. These are programmed into the Personality Module at the factory only.

The ECM Consists Of:

* A microprocessor, to perform the computing necessary to perform the ECM's functions (governing, controlling timing, generating diagnostic codes, communicating with service tools, ect.). The microprocessor gets its instructions from the software in the Personality Module.* Programmable Parameters, stored in permanent memory (both Customer Specified and System Configuration Parameters). Refer to the section 2.0 Programming Parameters for details on what these parameters do.* Logged Diagnostics, 3176 System logs certain diagnostic codes into memory so that a permanent record of the diagnostic is retained. Refer to the section Troubleshooting Diagnostic Codes, for further information on logged codes.* Input Circuits, to filter electrical noise from sensor signals and to protect sensitive internal circuits from potentially damaging voltage levels.* Output Circuits, to provide the high currents necessary to energize lamps or injector solenoids as the microprocessor chooses.* Power circuits, to provide clean stable electrical power to internal circuits and external sensors.

Diagnostic Codes

Functional Test

P-522: Engine Speed/Timing Circuit Test And Calibration

System Operation

The 3176 Speed/Timing Sensor provides pulse signals to the Electronic Control Module (ECM). The signals are created as the timing reference ring, mounted on the front of the camshaft drive gear, rotates past the pickup (sliphead) of the Speed/Timing Sensor. A unique tooth pattern on the timing reference ring allows the ECM to determine crankshaft position, as well as engine rpm. Minor changes in position of the sensor, relative to the timing reference ring, may occur whenever the sensor is moved or replaced. It is then necessary to calibrate the sensor. The sensor sliphead should also be extended before installing the sensor.

The sensor generates a pulse to the ECM as each tooth passes. The ECM counts the pulses to determine rpm, memorizes the pattern of the pulses and compares that pattern to a standard, in order to determine crankshaft position. Having located #1 cylinder, the ECM then triggers each unit injector in the correct firing order and at the correct time. The actual timing and duration of each injection is determined by the ECM according to engine rpm and load. A loss of the Speed/Timing Sensor signal results in termination of the signals to the fuel injectors thus causing the engine to stop.

The Speed/Timing Sensor receives 13.2 volts DC regulated and supplied by the ECM. It is not "Battery Voltage"; it is generated within the ECM, and is held within ± 1.0 volts DC. Power is supplied to the sensor at the 3-Pin connector (J9/P9) on pin-A (+V Engine Speed/Timing), and ground on pin-B (Engine Speed/Timing Common). The sensor signal routes to the ECM through pin-C (Engine Speed/Timing).

NOTE: If the Speed/Timing Wheel is installed wrong (flipped over), then code 190-02 Loss Of Engine rpm Signal (Diagnostic Code 34) will be generated and the ECM will not fire the injector solenoids.

NOTE: Unless the engine symptom such as misfire, speed burp, surging, etc., is accompanied by diagnostic code 190-02 Loss Of Engine RPM Signal (34), the malfunction is probably not caused by the engine speed/timing system.

Schematic

Diagnostic Codes

Functional Test

Example 3176: ECAP "Display Status Screen"

Engine Speed/Timing Sensor Calibration

Installed Magnetic Pick-up Sensor

3176: ECAP "Monitor/Calibrate Timing" Screen

P-523: Injector Solenoid Functional Test

System Operation

The 3176 Diesel Truck Engine utilizes Electronic Unit Injectors, which are mechanically actuated and electronically energized. The injectors can be individually cut out to aid in troubleshooting misfire problems.

Under certain conditions the 3176 Diesel Truck Engine may intentionally operate on only three cylinders. This feature is called "Three Cylinder Cutout" and occurs when the truck is operating at higher rpm under low or no load conditions (when signals to the unit injectors are of very short duration). During "Three Cylinder Cutout" operation, in order to obtain more precise fuel metering in cylinders #1, #2, and #3, the ECM does not signal fuel injection into cylinders #4, #5, and #6. When more power is needed, all six cylinders are fueled and full power is delivered by the engine. The change in feel and in sound during "cutout" operation is normal, but may be misdiagnosed as an engine problem.

The solenoid is mounted atop the injector body along side the tappet return spring.

Schematic

Diagnostic Codes

Functional Test

P-524: +5 Volt Sensor Supply Circuit Test

System Operation

The 3176 Electronic Control Module (ECM) supplies the Coolant Temperature, Inlet Air Temperature, Oil Pressure, and Coolant Level Sensors (if installed) with a regulated +5 volts DC from the same supply.

The +5 V sensor supply is routed from the ECM through P4/J4 pin 10 to pin A of connectors J10/P10 (Coolant Temperature Sensor), J21/P21 (Inlet Air Temperature Sensor), J17/P17 (Oil Pressure Sensor), and pin 18 of the Vehicle Connector J7/P7. The supply is 5 ± 0.5 volts DC. On engines with serial numbers 7LG1-7499 the Inlet Air Temp also routes through the Engine Harness to Extension Harness Connector J16/P16 and Harness Extension before reaching the Inlet Air Temperature Sensor Connector J21/P21.

NOTE: The diagnostic code described below will not appear on ECM part numbers 9X-7153, OR-6481, 9X-7154, or OR-6127. The 5V Short Circuit Diagnostic Code is most likely caused by a short circuit in the harness, next likely is a sensor, and least likely, the ECM itself. Even with Caterpillar Engine Protection programmed to the OFF mode, the Oil Pressure Sensor harness should be checked as described in the following test. Likewise, if the Coolant Level sensor is present, the sensor and associated OEM harness should be inspected. A short through these components' harness, or a sensor malfunction could cause a problem even though the sensors are not being used for engine control system purposes.

Schematic

Diagnostic Codes

Functional Test

P-525: Coolant Temperature Circuit Test

System Operation

The coolant temperature sensor measures the temperature of the engine coolant. The ECM uses this information to determine the mode of operation, and if Caterpillar Engine Protection is mode is not programmed "OFF", to notify the operator of an excessive engine coolant temperature.

Cold Mode is activated whenever coolant temperature is below 17°C (63°F). In Cold Mode engine power is limited, timing is retarded, and low idle is increased to 800 or 1000 rpm, to improve warm-up time. Once activated, Cold Mode will continue until coolant temperature rises above 28°C (82°F), or until the engine has been running for 12 minutes. The ECM then causes the engine to leave Cold Mode, low idle speed is returned to the rpm set by the Customer Specified Parameter, and normal engine operation is restored.

The sensor operates on 5 volts DC, supplied through pin 10 of the ECM connector J4/P4. Note that the +5 Volt Supply and Sensor Common are shared with the Inlet Air Temperature, and Oil Pressure sensors of the 3176 system. The +5 volt supply is also shared by the Coolant Level Sensor (if installed) that is OEM provided.

Schematic

Diagnostic Codes

Functional Test

P-526: Inlet Air Temperature Circuit Test

System Operation

The Inlet Air Temperature sensor measures the temperature of the inlet manifold air. The ECM monitors the Inlet Air Temperature sensor and Coolant Temperature Sensor signals to adjust injection timing. The Inlet Air Temperature Sensor does not affect Cold Mode low idle engine rpm like the Coolant Temperature Sensor.

The sensor operates on 5 volts DC, supplied through pin 10 of the ECM connector J4/P4. Note that the +5 volt supply and sensor common are shared with the Coolant Temperature, and Oil Pressure sensors of the 3176 system. The +5 volt supply is also shared by the Coolant Level Sensor (if installed) that is OEM provided.

NOTE: The sensor temperature will be affected by the conducted heat from the intake manifold when idling (or following engine shutdown). This warm up is due to the loss of circulating air through the intake manifold. Be aware tha the Inlet Air Temperature read from the sensor may be significantly higher than the actual temperature of the air within the intake manifold until the intake manifold cools.

NOTE: Some engines will have a harness extension connected from where the Fuel Pressure Sensor used to be (connector J16/P16) to the Inlet Air Temperature Sensor. Connector J16/P16 is now referred to as the Engine Harness to Extension Harness Connector.

NOTE: On engines with serial numbers 7LG1-7499, Inlet Air Temperature Sensors have Deutsch HD Connectors, 7LG7500-UP Inlet Air Temperature Sensors have DT Connectors.

Schematic

Diagnostic Codes

Functional Test

P-527: Oil Pressure Circuit Test

System Operation

The 3176 system monitors oil pressure with a sensor located in the oil gallery (right side of engine). The oil pressure sensor is supplied with electrical power by the 5 volt sensor supply voltage from the ECM.

Note that the 3176 uses oil pressure only as an engine protection function (available for 7LG7500-UP engines). Lack of oil pressure does not prevent the 3176 ECM from starting the engine. The 3176 ECM will still try to start the engine even if oil pressure is low.

The 3176 system monitors oil pressure following engine start up and may show a 100-01 Low Oil Pressure Warning Diagnostic Code (46). The Diagnostic Code will not be logged for the first 15 seconds following engine start up, only ACTIVE.

The Oil Pressure Sensor can measure oil pressure from 0 kPa (0 psi) to 690 kPa (100 psi).

The 3176 oil pressure sensor is supplied with electrical power by the 5 volt sensor supply voltage from the ECM through connector J4/P4 Pin 10 to the Oil Pressure Sensor Connector P17/J17 Pin A. The Oil Pressure Sensor signal line routes from P17/J17 Pin C to J4/P4 pin 27. The Sensor Common routes from J4/P4 Pin 35 to P17/J17 pin B.

NOTE: the +5 V supply is shared with the Coolant Temperature, Inlet Air Temperature, and Coolant Level (if installed) Sensors. The Sensor Common is shared by the Coolant Temperature, and Inlet Air Temperature Sensors.

Schematic

Diagnostic Codes

Functional Test

ECAP Example Screen of Oil Pressure Reading

P-528: Boost Pressure Circuit Test And Sensor Calibration

System Operation

The 3176 system monitors boost pressure with a sensor located inside the Transducer Module. The boost pressure sensor is supplied with electrical through the Transducer Module Connector (inside the module) pin 1 (+8V). The signal routes through pin 2 (Boost Pressure) and Sensor Common is pin 3. The sensor can only be replaced by replacing the transducer module.

The boost pressure is used to reduce smoke emissions during acceleration. 3176 limits the amount of fuel injected until certain boost pressures are reached. It does this by converting boost pressure to "FRC Fuel Post." (as shown on the ECAP status display). The FRC Fuel Pos. is electronic limit on the amount of fuel injected and is based on a ratio of fuel to air being supplied to the cylinders. It operates in a manner similar to the fuel ratio control on an engine with a mechanical governor.

The inlet air hose from the air cleaner to the transducer module must be installed. The air inlet serves as a vent for the transducer module and is required for proper operation of the boost pressure sensor.

The 3176 Boost Pressure Sensor must be calibrated for a zero boost condition with the engine off. Calibration is accomplished electronically without the need for manual adjustments. The sensor must be recalibrated whenever the ECM or transducer module has been replaced in order to avoid poor engine response.

NOTE: For calibration of Boost Pressure Sensor, see Step 3 of this procedure.

Schematic

Diagnostic Codes

Functional Test

Example Screen for Boost Pressure Sensor Calibration.

P-529: Atmospheric Pressure Sensor Test

System Operation

NOTE: The Atmospheric Pressure Sensor is part of a High Altitude Package, and not found on most engines. Only Transducer Modules with Part Number 3E8644 contain the Atmospheric Pressure sensor.

The 3176 system monitors atmospheric pressure with a sensor located inside the transducer module. The atmospheric pressure sensor is supplied with electrical power by the 8 volt sensor supply from the ECM. The sensor can only be replaced by replacing the Transducer Module.

Atmospheric pressure is used to reduce smoke emissions at high altitudes. The 3176 optimizes timing based on engine operating conditions.

The inlet air hose from the air cleaner to the Transducer Module should be installed to provide air source for the inlet air vent. The air inlet serves as a vent for the transducer module and is required for proper operation of the atmospheric pressure sensor.

The 3176 atmospheric pressure sensor cannot be calibrated.