C4.4 and C6.6 Engines Caterpillar


Speed Control (PWM) - Test

Usage:

C4.4 448
Use this procedure if the digital throttle position sensor is suspected of incorrect operation. This procedure also covers the following diagnostic codes:

Table 1
Diagnostic Trouble Codes for the Digital Throttles 
J1939 Code  CDL Code  Code Description
(code descriptions may vary) 
Comments 
29-3  774-3  Accelerator Pedal Position 2 : Voltage Above Normal  The Electronic Control Module (ECM) detects the following conditions:

The ECM has been powered for 3 seconds.

Diagnostic code 168-4 is not active.

There are no active 678 or 41 codes.

The setting for the upper diagnostic limit has been exceeded for one second.

If equipped, the warning lamp will come on. The diagnostic code will be logged. 
29-4  774-4  Accelerator Pedal Position 2 : Voltage Below Normal  The ECM detects the following conditions:

The ECM has been powered for 3 seconds.

Diagnostic code 168-4 is not active.

There are no active 678 or 41 codes.

The setting for the lower diagnostic limit has been exceeded for one second.

If equipped, the warning lamp will come on. The diagnostic code will be logged. 
29-8  774-8  Accelerator Pedal Position 2 : Abnormal Frequency, Pulse Width or Period  The ECM detects the following conditions:

The signal frequency from the digital throttle position sensor is equal to 0% or 100% for more than 2 seconds.

The ECM has been powered for at least 3 seconds.

Diagnostic codes 29-3, 774-3, 29-4, and 774-4 are not active.

There are no active 678 or 41 codes.

The ECM sets the Throttle Position to "0%".
If equipped, the warning lamp will come on. The diagnostic code will be logged if the engine is running. The diagnostic code will not be logged if the engine is cranking. 
91-3  91-3  Accelerator Pedal Position 1 : Voltage Above Normal  The Electronic Control Module (ECM) detects the following conditions:

The ECM has been powered for 3 seconds.

Diagnostic code 168-4 is not active.

There are no active 678 or 41 codes.

The setting for the upper diagnostic limit has been exceeded for one second.

If equipped, the warning lamp will come on. The diagnostic code will be logged. 
91-4  91-4  Accelerator Pedal Position 1 : Voltage Below Normal  The ECM detects the following conditions:

The ECM has been powered for 3 seconds.

Diagnostic code 168-4 is not active.

There are no active 678 or 41 codes.

The setting for the lower diagnostic limit has been exceeded for one second.

If equipped, the warning lamp will come on. The diagnostic code will be logged. 
91-8  91-8  Accelerator Pedal Position 1 : Abnormal Frequency, Pulse Width or Period  The ECM detects the following conditions:

The signal frequency from the digital throttle position sensor is equal to 0% or 100% for more than 2 seconds.

The ECM has been powered for at least 3 seconds.

Diagnostic codes 91-3 and 91-4 are not active.

There are no active 678 or 41 codes.

The ECM sets the Throttle Position to "0%".
If equipped, the warning lamp will come on. The diagnostic code will be logged if the engine is running. The diagnostic code will not be logged if the engine is cranking. 
Follow the troubleshooting procedure to identify the root cause of the fault. 

If a fault occurs with the primary throttle, the engine will use the secondary throttle until the fault is repaired.

If a fault occurs with the secondary throttle, the engine will use the primary throttle until the fault is repaired.

If a functional throttle is not available, the following conditions will occur:

  • The engine will default to the limp home speed.

  • If the engine speed is higher than the limp home speed, the engine will decelerate to the limp home speed.

  • If the engine speed is lower than the limp home speed, the engine speed will remain at the current speed.

  • The engine will remain at this speed while the diagnostic code remains active.

  • All inputs from the faulty throttle are ignored by the ECM until the fault is repaired.

  • All inputs from the repaired throttle will be ignored by the ECM until the keyswitch has been cycled.

Digital Throttle Position Sensor

The digital throttle position sensor is used to provide a digital throttle position signal to the ECM. The sensor output is a constant frequency signal with a pulse width that varies with the throttle position. This output signal is referred to as either a duty cycle or a pulse width modulated signal (PWM). This output signal is expressed as a percentage between 0 and 100 percent.

The digital throttle position sensor is most likely to be attached directly to the throttle assembly. The digital throttle position sensor requires no adjustment.

The duty cycle at low idle and the duty cycle at high idle can vary depending on the application. The percent of duty cycle is translated in the ECM into a throttle position of 3 to 100 percent.

The digital throttle position sensors are powered by +8 VDC from the ECM. The supply voltage is from J1: to the digital throttle position sensor connector.

If the application is using the ECM dedicated PTO functions, the digital throttle position sensor will be ignored while the engine is in PTO mode.

The ECM is in PTO mode if the PTO ON/OFF Switch is ON. This status can be checked with the electronic service tool. Refer to Troubleshooting, "Power Take-Off - Test" for testing if the PTO is being used.

Note: The identification letters for the terminals in the connectors may vary dependent on the manufacturer of the throttle pedal.



Illustration 1g06104803

Table 2
Required Tools 
Tool  Part Number  Part Description  Qty 
326-4904  Adapter Cable As 

During the following procedure, refer to the electrical schematic for the application.

Complete the procedure in the order in which the steps are listed.

Table 3
Troubleshooting Test Steps  Values  Results 

1. Inspect Electrical Connectors and Wiring

A. Thoroughly inspect the terminal connections on the P1/J1 ECM connector and the PWM throttle position sensors. Refer to Troubleshooting, "Electrical Connector - Inspect".

B. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the PWM throttle position sensor connector.

C. Check the screw for the ECM connector for the correct torque of 6 N·m (53 lb in).

D. Check the harness for corrosion, abrasion, and pinch points from the PWM throttle position sensor to the ECM.
 

Loose connection or damaged wire
 

Result: There is a fault in a connector or the wiring.

Repair: Repair any faulty connectors or replace the wiring harness. Ensure that all the seals are properly in place and ensure that the connectors are correctly coupled.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: All connectors, pins, and sockets are correctly coupled and/or inserted. The harness is free of corrosion, abrasion, and pinch points.

Proceed to Test Step 2.
 

2. Check for Active Diagnostic Codes

A. Turn the keyswitch to the OFF position.

B. Connect the electronic service tool to the diagnostic connector.

C. Turn the keyswitch to the ON position. Wait at least 10 seconds for activation of the diagnostic codes.

D. Verify if any of the diagnostic codes that are listed in Table 1 are active.
Note: When the ECM calibrates duty cycle values for the low and high idle throttle positions, the ECM assumes the initial lower position for the duty cycle at low idle and the initial upper position for the duty cycle at high idle. The initial lower position and the initial upper position can be obtained by accessing the following screens on the electronic service tool:
· Service
· Throttle Configuration
· "Throttle# 1"
As a result, the throttle position status may reach 100 percent well before the throttle pedal is fully depressed. This situation is normal. Cycle the throttle to the high idle position several times for the ECM to adjust the calibration automatically. During normal operation, more movement of the throttle can be required for the throttle position status to increase above 3 percent. The status may reach the 100 percent value prior to the limit of the high idle position. This process is done to ensure that the throttle reaches these two critical points for engine operation.

E. Turn the keyswitch to the OFF position.
 

Diagnostic codes
 

Result: At least one of the diagnostic codes listed in Table 1 is active.

Proceed to Test Step 4.

Result: None of the preceding diagnostic codes are active or recently logged - There may be an intermittent fault.

Repair: Refer to Troubleshooting, "Electrical Connector - Inspect" to identify intermittent faults.

If the fault is still present, proceed to Test Step 3.
 

3. Check the Duty Cycle of the Digital Throttle Position Sensor

A. Access the following screens on the electronic service tool to check the upper and the lower diagnostic limit of the throttle position sensors:
· "Service"
· "Throttle Configuration"
· "Throttle# 1"

B. Make a note of the lower diagnostic limit and the upper diagnostic limit.

C. Verify that the keyswitch is in the ON position.

D. Access the following screens on the electronic service tool to monitor the duty cycle of the throttle position:
· "Status"
· "Throttles"

E. Monitor the duty cycle of the throttle at the "low idle" position and the "high idle" position.
 

Duty cycle above lower diagnostic limit at low idle

Duty cycle below upper diagnostic limit at high idle
 

Result: The digital throttle position sensor is operating correctly.

Return the engine to service.

Result: The digital throttle position sensor circuit is not operating correctly.

Proceed to Test Step 4.
 

4. Check the Supply Voltage at the Digital Throttle Position Sensor

A. Turn the keyswitch to the OFF position.

B. Install Tooling (A) on the suspect digital throttle position sensor connector.

C. Turn the keyswitch to the ON position.

D. Measure the voltage between the +8 VDC terminal and the sensor return terminal on Tooling (A).
 

7.5 VDC to 8.5 VDC
 

Result: The sensor supply voltage is not within the expected range. The fault is in the sensor supply wiring or the ground wiring between the sensor and the ECM.

Repair: Repair the faulty wiring or replace the faulty wiring.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: The sensor supply voltage is within the expected range.

Proceed to Test Step 5.
 

5. Check the Duty Cycle of the Throttle Position Sensor at the Sensor

Note: Performing certain steps within this procedure requires the use of a multimeter that can measure a PWM duty cycle.

A. Access the following screens on the electronic service tool to check the upper and the lower diagnostic limit of the suspect throttle position sensors:
· "Service"
· "Throttle Configuration"
· "Throttle# 1"

B. Make a note of the lower diagnostic limit and the upper diagnostic limit.

C. Turn the keyswitch to the OFF position.

D. Remove the signal wire for the suspect digital throttle position sensor from the sensor connector.

E. Install Tooling (A) on the digital throttle position sensor connector.

F. Connect the multimeter probes to the sensor signal terminal and the sensor ground terminal of Tooling (A).

G. Turn the keyswitch to the ON position.

H. While the duty cycle is being monitored on the multimeter, operate the throttle through the full range of movement.
 

Duty cycle above lower diagnostic limit at low idle

Duty cycle below upper diagnostic limit at high idle
 

Result: Not OK.

Repair: Replace the suspect digital throttle position sensor.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: OK.

Proceed to Test Step 6.
 

6. Bypass the Signal Wire

A. Turn the keyswitch to the OFF position.

B. Disconnect the suspect digital throttle position sensor connector. Disconnect the P1 connector from the ECM.

C. Remove the sensor signal wire from the connector for the suspect digital throttle position sensor. Remove the applicable signal wire from the P1 connector.

D. Install the jumper wire between the applicable signal terminal on the P1 connector and the signal terminal on the suspect throttle sensor connector.

E. Access the following screens on the electronic service tool to check the upper and the lower diagnostic limit of the throttle position sensor:
· "Service"
· "Throttle Configuration"
· "Throttle# 1"

F. Make a note of the lower diagnostic limit and the upper diagnostic limit.

G. Turn the keyswitch to the ON position.

H. Check the duty cycle of the position sensor on the electronic service tool while the digital throttle is being moved over the full range.
 

Duty cycle above lower diagnostic limit at low idle

Duty cycle below upper diagnostic limit at high idle
 

Result: OK - The throttle operates correctly with the bypass installed. The fault is in the sensor signal wiring.

Repair: Repair the faulty wiring or replace the faulty wiring.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: Not OK

Repair: Recheck the wiring, the ECM connectors, and the digital throttle position sensor connector.

If no faults are found, contact the Dealer Solutions Network (DSN).
 

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