Use this procedure to troubleshoot the electrical system if a problem is suspected with the throttle position sensor or if the diagnostic code in Table 1 is active or easily repeated.
| Diagnostic Codes Table | ||
|---|---|---|
| Code and Description | Conditions which Generate this Code | System Response |
| 91-8 Throttle Position Sensor abnormal frequency, pulse width, or period | The Electronic Control Module (ECM) detects an incorrect duty cycle on the throttle signal. The duty cycle is less than 40 percent or the duty cycle is greater than 61 percent. | The code is logged. The ECM flags the throttle position as invalid data and a default value of zero percent is used. The engine speed is limited to low idle. |
| 264-8 Deceleration Throttle abnormal frequency, pulse width, or period | The ECM detects an incorrect duty cycle or frequency on the throttle signal. The duty cycle is less than 5 percent or the duty cycle is greater than 95 percent. The frequency is less than 150 Hz or the frequency is greater than 1000 Hz. | The code is logged. The ECM sets the throttle to 650 rpm at start-up. The ECM keeps the throttle at the last speed if the speed is less than 1000 rpm. The ECM drops the throttle to 1000 rpm if the speed is more than 1000 rpm. |
The throttle position sensor provides the throttle signal to the ECM. The throttle position sensor is mounted to a pedal assembly that allows the operator to control the speed of the engine. The geometry of the pedal assembly controls both the travel of the sensor and the range of the output signal. The throttle position sensor cannot be adjusted.
The output from the throttle position sensor is a Pulse Width Modulated (PWM) signal that varies with the position of the throttle pedal. The throttle position sensor produces a minimum duty cycle in the released position and a maximum duty cycle in the fully depressed position. When the pedal is released, the ECM translates the sensor's output signal to a throttle position of 0 percent. When the pedal is fully depressed, the ECM translates the output signal to a throttle position of 100 percent.
The throttle position sensor is powered by 8.0 ± 0.4 VDC that is provided by the ECM. A digital return for the sensor is also provided by the ECM.
The ECM uses an automatic calibration function that allows the ECM to minimize the deadband of the sensor. The automatic calibration function assumes a range of PWM duty cycle at powerup. If the duty cycle of the sensor exceeds this initial range, the automatic calibration function adjusts the limits of the duty cycle in order to adjust for the new range.
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| Illustration 1 | g01395896 |
Schematic for the throttle position sensor | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Remove electrical power from the ECM.
- Thoroughly inspect the J1/P1 ECM connector and the J2/P2 ECM connector. Inspect all of the connectors that are associated with the circuit.
Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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| Illustration 2 | g01139425 |
ECM (1) J1/P1 connectors (2) J2/P2 connectors | |
- Perform a 45 N (10 lb) pull test on each of the wires in the circuit.
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| Illustration 3 | g01395911 |
P1 ECM connector (P1-35) + 8 V digital supply (P1-29) Digital return | |
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| Illustration 4 | g01395912 |
P2 ECM connector (P2-24) Throttle position | |
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| Illustration 5 | g01159881 |
Connector for the throttle position sensor (A) +8 V supply (B) Digital return (C) Throttle position | |
- Check the allen head screw from each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque value.
- Check the harness and the wiring for abrasion and for pinch points.
Expected Result:
All of the connectors, pins and sockets are completely coupled and/or inserted and 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 - The connectors and/or wiring are not OK.
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 Throttle Pedal Assembly
- Inspect the throttle pedal assembly for components that are loose, bent, missing, or worn.
- Slowly depress the pedal and release the pedal.
Expected Result:
The throttle pedal assembly operates smoothly without excessive drag. The pedal springs back smoothly to the low idle position without assistance.
Results:
- OK - The throttle pedal assembly functions properly. Proceed to Test Step 3.
- Not OK - The throttle pedal assembly is in poor repair.
Repair: Repair the throttle pedal assembly or replace the throttle pedal assembly, as required.
STOP
Test Step 3. Check the Status for "Throttle Position"
- Connect Caterpillar Electronic Technician (ET) to the service tool connector.
- Restore electrical power to the ECM.
- Observe the status for "Throttle Position" on Cat ET while you operate the throttle pedal through the entire range of travel.
Expected Result:
The status is zero percent when the throttle pedal is released. The status progressively increases to 100 percent when the throttle pedal is fully depressed.
Results:
- OK - The throttle position sensor is working properly.
Repair: There may be an intermittent electrical problem with the harness or the connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.
STOP
- Not OK - The throttle position that is displayed on Cat ET does not correspond to the movement of the throttle pedal. Proceed to Test Step 4.
Test Step 4. Check the Supply Voltage at the Sensor
- Remove electrical power from the ECM.
- Disconnect the connector for the throttle position sensor.
- Restore electrical power to the ECM.
- Measure the voltage across terminal A (+8 V supply) and terminal B (digital return) on the harness side of the connector.
- Remove electrical power from the ECM.
Expected Result:
The supply voltage measures 8.0 ± 0.4 VDC at the sensor connector.
Results:
- OK - The correct voltage is measured at the sensor connector. The sensor is receiving the correct supply voltage. Proceed to Test Step 5.
- Not OK - The voltage is not correct at the sensor connector. The sensor is not receiving the correct supply voltage. Proceed to Test Step 7.
Test Step 5. Check the Duty Cycle at the Sensor
- Install a 7X-6370 Adapter Cable As (3-PIN BREAKOUT) at the connector for the throttle position sensor.
- Remove the signal wire from terminal C of the connector for the throttle position sensor. Remove the wire from the harness side of the connector.
- Restore electrical power to the ECM.
- Measure the duty cycle between terminal B (digital return) and terminal C (throttle position) at the 7X-6370 Adapter Cable As (3-PIN BREAKOUT) while you operate the throttle pedal.
- Remove electrical power from the ECM.
- Remove the breakout harness. Restore the wires to the original configuration.
Expected Result:
The duty cycle is between 40 and 61 percent.
Results:
- OK - The duty cycle is within specifications for the entire range of the pedal. The sensor is producing a valid signal. Proceed to Test Step 6.
- Not OK - The duty cycle is not within specifications.
Repair: The sensor is not producing a valid signal. Replace the throttle position sensor. Verify that the repair eliminates the problem.
STOP
Test Step 6. Check the Duty Cycle at the ECM
- Remove the throttle signal wire from ECM connector P2-24.
- Restore electrical power to the ECM.
- Measure the duty cycle of the sensor. Measure the duty cycle between wire P2-24 and P1-29 while you operate the throttle pedal.
- Remove electrical power from the ECM.
Expected Result:
The duty cycle is between 40 and 61 percent.
Results:
- OK - The duty cycle is within specifications for the entire range of the pedal.
Repair: A valid signal appears at the ECM, but the ECM is not reading the signal properly. Replace the ECM. Refer to Troubleshooting, "ECM - Replace" for complete instructions. Verify that the repair eliminates the problem.
STOP
- Not OK - The frequency and the duty cycle are not within specifications.
Repair: There is not a valid signal at the ECM connector. Repair the signal wire in the harness. Verify that the repair eliminates the problem.
STOP
Test Step 7. Check the +8 V Supply at the ECM
- Disconnect the J1/P1 ECM connector.
- Remove the +8 V supply wire from terminal P1-35 and remove the digital return wire from P1-29. Install jumper wires into the terminal locations for the digital return wire and the supply wire.
- Reconnect the J1/P1 ECM connector.
- Restore electrical power to the ECM.
- Measure the voltage between the wire jumpers in terminals P1-35 and P1-29.
- Remove electrical power from the ECM.
Expected Result:
The supply voltage measures 8.0 ± 0.4 VDC at the ECM.
Results:
- OK - The correct voltage is measured at the ECM.
Repair: There is a problem in the harness between the ECM and the sensor. Repair the harness or replace the harness. Verify that the repair eliminates the problem.
STOP
- Not OK - The voltage is not correct at the ECM.
Repair: The ECM does not appear to be producing the correct supply voltage. Replace the ECM. Refer to Troubleshooting, "ECM - Replace" for complete instructions. Verify that the repair eliminates the problem.
STOP