Use this procedure to troubleshoot any suspect problems with the decelerator position sensor.
This procedure covers the diagnostic code.
264-08 Decel Throttle Position signal abnormal
The decelerator position sensor is located behind the pedal assembly for the decelerator pedal in the cab of the machine.
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| Illustration 1 | g01250749 |
Location of the decelerator position sensor (typical location) | |
The decelerator position sensor provides a pulse width modulated signal that varies with the position of the decelerator. The Electronic Control Module (ECM) translates the signal into a percentage of the decelerator position sensor. Caterpillar Electronic Technician (ET) can be used in order to display this percentage as "Decelerator Position". The range for "Decelerator Position" is 0 to 100 percent.
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| Illustration 2 | g01276499 |
Schematic for the decelerator position sensor | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect the J1/P1 ECM connectors, the machine connectors, and the connectors for the decelerator position sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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| Illustration 3 | g01183529 |
Location of the J1/P1 ECM connectors (typical left side engine view) | |
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the sensor connectors that are associated with the active diagnostic code.
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| Illustration 4 | g01250748 |
P1 ECM connector (P1-4) +8 V digital supply (P1-5) Digital return (P1-66) Decelerator position | |
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| Illustration 5 | g01159881 |
Terminal locations at the connector for the decelerator position sensor (Terminal A) +8 V digital supply (Terminal B) Digital return (Terminal C) Decelerator position | |
- Check the allen head screw for each of the ECM connectors and the machine connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- Check the harness and wiring for abrasions and for pinch points from the sensor back to the ECM.
Expected Result:
All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, of abrasion, and of pinch points.
Results:
- OK - The harness and connectors appear to be OK. Proceed to Test Step 2.
- Not OK - There is a problem in the connectors and/or wiring.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.
STOP
Test Step 2. Inspect the Decelerator Pedal Assembly
- Inspect the decelerator pedal assembly for components that are loose, bent, missing, or worn.
- Slowly depress the pedal and release the pedal.
Expected Result:
The decelerator pedal assembly operates smoothly without excessive drag. The pedal returns to the fully released position without assistance in less than one second.
Results:
- OK - The decelerator pedal assembly functions properly. Proceed to Test Step 3.
- Not OK - There is a mechanical problem with the decelerator pedal assembly.
Repair: Repair the decelerator pedal assembly, as required.
STOP
Test Step 3. Check the Status for "Decelerator Position"
- Connect the Cat ET to the service tool connector.
- Turn the keyswitch to the ON position.
- Observe the status for "Decelerator Position" on Cat ET while you operate the decelerator pedal.
- Turn the keyswitch to the OFF position.
Expected Result:
The status is approximately 0 percent when the decelerator pedal is released. The status progressively increases to 100 percent when the decelerator pedal is fully depressed.
Note: This range can change depending on the adjustment of the decelerator pedal assembly.
Results:
- OK - The decelerator position sensor is working properly.
Repair: There may be an intermittent electrical problem in the harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting the problem.
STOP
- Not OK - The status is not correct on Cat ET. There may be a problem with the decelerator position sensor. Proceed to Test Step 4.
Test Step 4. Check the Supply Voltage at the Sensor
- Disconnect the connectors for the decelerator position sensor.
- Turn the keyswitch to the ON position.
- Measure the voltage between terminals A and B on the harness side of the sensor connector.
- Turn the keyswitch to the OFF position.
Expected Result:
The voltage is 8.0 ± 0.5 VDC.
Results:
- OK - The voltage is 8.0 ± 0.5 VDC. The voltage is correct. Proceed to Test Step 5.
- Not OK - The voltage is not 8.0 ± 0.5 VDC.
Repair: The supply voltage is not reaching the sensor. Refer to Troubleshooting, "Digital Sensor Supply Circuit - Test" for information that is related to troubleshooting the digital sensor supply.
STOP
Test Step 5. Check the Signal Frequency and the Duty Cycle at the Sensor
- Remove the wire from terminal C (signal) on the harness side of the connector for the decelerator position sensor.
- Install a 7X-6370 Adapter Cable As (3-PIN BREAKOUT) at the connector. Connect the connectors for the sensor.
- Turn the keyswitch to the ON position.
- Use a multimeter to measure the signal frequency and the duty cycle between terminal B (digital return) and terminal C (signal) at the breakout while you operate the decelerator pedal.
- Turn the keyswitch to the OFF position.
- Remove the breakout from the circuit. Restore the wiring to the original configuration.
Expected Result:
The frequency is between 150 and 1000 Hz. The duty cycle is approximately 57 percent when the pedal is released. The duty cycle is approximately 32 percent when the pedal is fully depressed.
Results:
- OK - The signal frequency and the duty cycle are correct. The sensor is producing a valid signal. Proceed to Test Step 6.
- Not OK - The signal frequency and/or the duty cycle are not correct.
Repair: The sensor is not producing a valid signal. Replace the decelerator position sensor. Verify that the repair eliminates the problem.
STOP
Test Step 6. Check the Signal Frequency and the Duty Cycle at the ECM
- Disconnect the J1/P1 ECM connector.
- Install a 208-0059 Adapter Cable As (70-PIN BREAKOUT) at the J1/P1 ECM connector.
- Connect the J1/P1 ECM connector.
- Turn the keyswitch to the ON position.
- Measure the frequency and the duty cycle between terminal P1-66 (decelerator position) and terminal P1-5 (digital return) at the breakout while you operate the decelerator.
- Turn the keyswitch to the OFF position.
Expected Result:
The frequency is between 150 and 1000 Hz. The duty cycle is approximately 57 percent when the pedal is released. The duty cycle is approximately 32 percent when the pedal is fully depressed.
Results:
- OK - The signal frequency and the duty cycle are correct. A valid sensor signal is reaching the ECM. Proceed to Test Step 7.
- Not OK - The signal frequency and/or the duty cycle are not correct.
Repair: A valid sensor signal is not reaching the ECM. There is a problem in the harness between the sensor connector and the ECM connector. Repair the wiring harness and/or the connectors. Verify that the repair eliminates the problem.
STOP
Test Step 7. Check the Status for "Decelerator Position"
- Turn the keyswitch to the ON position.
- Observe the status for "Decelerator Position" on Cat ET while you operate the decelerator pedal.
Expected Result:
The status reads approximately 0 percent when the decelerator pedal is released. The status progressively increases to 100 percent when the decelerator pedal is fully depressed.
Note: This range can change depending on the adjustment of the decelerator pedal assembly.
Results:
- OK - The status for "Decelerator Position" is correct.
Repair: The decelerator position sensor is working properly at this time. There may be an intermittent electrical problem in the wiring harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting intermittent electrical problems.
STOP
- Not OK - The status for "Decelerator Position" is not correct.
Repair: A valid signal is available to the ECM, but the ECM is not detecting the signal properly. There is a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.
STOP