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-300: 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.
Functional Test
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 (44 N) pull test on each pin/wire.
Each pin and connector should easily withstand 10 pounds (44 N) 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-301: 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, the 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. See Electronic Troubleshooting, 3176 Diesel Truck Engine, Form No. SENR5112-01, procedure P:510 Electrical Power Supply To The 3176 ECM Test for a means of bypassing vehicle wiring.
Schematic
Diagnostic Codes
Functional Test
P-302: Throttle Position Sensor Test
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 is supplied by Caterpillar, and installed by the truck manufacturer. 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. Initial adjustment of the Remote Mounted Throttle Position Sensor is the responsibility of the truck manufacturer. The "pedal mounted" sensor is attached directly to the pedal and requires no adjustment. Both sensors provide the same type signal to the ECM.
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. This adjustment must be made using either a Digital Diagnostic Tool (DDT) or an Electronic Control Analyzer Programmer (ECAP). The pedal mounted sensor produces 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%.
NOTE: The pedal mounted throttle position sensor (PMTPS) cannot be adjusted as the remote mounted throttle position sensor (RMTPS) must be. The above "Duty Cycle" information for the PMTPS is the range the pedal manufacturer uses when assembling the sensor into their pedal assembly.
Schematic
Diagnostic Codes
Functional Test
P-303: Vehicle Speed Signal Test
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
P-304: Cruise Control And PTO Switches 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:
NOTE: For Personality Modules dated OCT91 or newer, the Set and Resume switches are Customer Programmable for Set/Accel - Resume/Decel or Set/Decel - Resume/Accel.
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 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 in Cruise Mode, 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 in Cruise Mode, 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 typically in the truck cab, and are supplied by the OEM. To troubleshoot the On/Off, Set, or Resume switches, use this procedure. To troubleshoot the Clutch or Brake switches, use P-405: Service Brake And Clutch Switch Test.
Voltage at each of the inputs to the ECM should be 5.0 plus or minus .5 volts with the switch Off, and less than .5 volts with the switch On.
Schematic
Functional Test
Table A
P-305: Service Brake And Clutch Switch 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
Table B
P-306: Parking Brake Switch Test
System Operation
The Parking Brake switch is used only to enable the Idle Shutdown Timer. 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
Table C
P-307: 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-308: Coolant Level Sensor 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).
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 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
P-309: 3176 Diagnostic/Warning Lamp 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/OFF as long as the fault is ACTIVE.
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 2 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-310: J1922 Powertrain Data Link
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 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.
Failure 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, with a baud rate of 9600. 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 a twisted pair 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
