Use this procedure to troubleshoot the electrical system if a problem is suspected with the throttle position sensor. Also, use this procedure if one of the diagnostic codes in Table 1 is active.
Diagnostic Trouble Codes | ||
---|---|---|
J1939 Code and Description | Conditions that Generate the Code | System Response |
29-2 Accelerator Pedal Position 2 : Erratic, Intermittent, or Incorrect | The Electronic Control Module (ECM) detects an erratic signal in the circuit for the #2 throttle position sensor. | The code is logged. |
29-3 Accelerator Pedal Position 2 : Voltage Above Normal | The ECM detects a voltage that is above normal in the circuit for the #2 throttle position sensor. | The code is logged. |
29-4 Accelerator Pedal Position 2 : Voltage Below Normal | The ECM detects a voltage that is below normal in the circuit for the #2 throttle position sensor. | The code is logged. |
29-8 Accelerator Pedal Position 2 : Abnormal Frequency, Pulse Width, or Period | The ECM detects an incorrect frequency or an incorrect duty cycle in the circuit for the #2 throttle signal. | The engine speed is limited to low idle.
The code is logged. |
91-2 Accelerator Pedal Position 1 : Erratic, Intermittent, or Incorrect | The ECM detects an erratic signal in the circuit for the #1 throttle position sensor. | The code is logged. |
91-3 Throttle Position Sensor : Voltage Above Normal | The ECM detects a voltage that is above normal in the circuit for the #1 throttle position sensor. | The code is logged. |
91-4 Throttle Position Sensor : Voltage Below Normal | The ECM detects a voltage that is below normal in the circuit for the #1 throttle position sensor. | The code is logged. |
91-8 Throttle Position Sensor : Abnormal Frequency, Pulse Width, or Period | The ECM detects an incorrect frequency or an incorrect duty cycle in the circuit for the #1 throttle signal. | The engine speed is limited to low idle.
The code is logged. |
The throttle position sensors provide the throttle signal to the ECM.
Each throttle position sensor allows the operator to control the speed of the engine. The geometry of the throttle assembly controls both the travel of the sensor and the range of the output signal. The throttle position sensors cannot be adjusted.
The ECM recognizes the signal from the throttle position sensor according to the strategy that is set up in the configuration parameters. Refer to Troubleshooting, "Configuration Parameters" for details that relate to the current throttle strategy settings.
The output from the throttle position sensor is a PWM signal that varies with the position of the throttle assembly. The throttle position sensor produces a minimum duty cycle in the released position and a maximum duty cycle in the fully actuated position. When the sensor is released, the ECM translates the sensor output signal to a throttle position of 0 percent. When the sensor is fully actuated, 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 adjusts the limits to adjust for the new range.
Illustration 1 | g02160270 |
Schematic for throttle position sensors |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
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Illustration 2 g02133295 Location of the J1/P1 ECM connectors (typical engine view)
(1) J1/P1 ECM connectors - Thoroughly inspect ECM connectors (1). Also, thoroughly inspect the connector for the throttle position sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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Illustration 3 g02160290 Terminal locations at the P1 ECM connector for the throttle position sensor
(P1-1) Throttle position
(P1-4) 8 V supply
(P1-5) Digital return
(P1-66) Throttle positionShow/hide tableIllustration 4 g02137756 Terminal locations for the throttle position sensor (typical example)
(Terminal 1) 8 V supply
(Terminal 2) Digital return
(Terminal 3) Throttle position - Perform a
45 N (10 lb) pull test on each of the wires in the ECM connector and the connector for the throttle position sensor. - 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 coupled and/or inserted and the wiring is free of corrosion, of abrasion, and 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 coupled.
Verify that the repair eliminates the problem.
STOP
Test Step 2. Inspect the Throttle Assembly
- Inspect the throttle assembly for components that are loose, bent, missing, or worn.
- Slowly actuate the throttle and release the throttle.
Expected Result:
The throttle assembly operates smoothly without excessive drag. The throttle assembly springs back smoothly to the low idle position without assistance.
Results:
- OK - The throttle assembly functions properly. The throttle assembly is OK. Proceed to Test Step 3.
- Not OK - The throttle assembly is in poor repair.
Repair: There is excessive drag or improper operation of the throttle assembly. Repair the throttle assembly or replace the throttle assembly, as required.
STOP
Test Step 3. Check the Status for "Throttle Position" on Caterpillar Electronic Technician (ET)
- Connect the Cat ET to the service tool connector.
- Turn the keyswitch to the ON position.
- Observe the status for either "Throttle Position" or "Throttle #2 Position" on Cat ET. Operate the throttle through the entire range of travel.
Expected Result:
The status is zero percent when the throttle is released. The status progressively increases to 100 percent when the throttle is fully actuated.
Results:
- OK - The throttle position sensor is working properly.
Repair: The original problem seems to be resolved. 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 is questionable. Proceed to Test Step 4.
Test Step 4. Check the Supply Voltage at the Sensor
- Turn the keyswitch to the OFF position.
- Disconnect the harness connector for the throttle position sensor.
- Turn the keyswitch to the ON position.
- Measure the voltage across terminal 1 (8 V supply) and terminal 2 (digital return) on the harness side of the connector.
- Turn the keyswitch to the OFF position.
Expected Result:
The supply voltage measures 8.0 ± 0.4 V 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.
Repair: There may be a problem with the sensor supply. Refer to Troubleshooting, "Sensor Supply - Test" for information that is related to troubleshooting the supply circuit.
STOP
Test Step 5. Check the Signal Frequency and the Duty Cycle at the Sensor
- Remove the wire from terminal location C (throttle position) on the harness side of the connector for the suspect throttle position sensor.
- Install a 3-pin breakout at the connector for the throttle position sensor.
- Connect the connector for the throttle position sensor.
- Turn the keyswitch to the ON position.
- Measure the frequency and the duty cycle between terminal 2 (digital return) and 3 (throttle position) at the 3-pin breakout while you operate the throttle.
- Turn the keyswitch to the OFF position.
- Remove the breakout harness. Restore the wiring for the harness connector to the original configuration.
Expected Result:
The frequency is between 150 and 1000 Hz. The duty cycle is between 7 and 95 percent.
Results:
- OK - The frequency and the duty cycle are within specifications for the entire range of the throttle. The sensor is producing a valid signal. Proceed to Test Step 6.
- Not OK - The frequency and the duty cycle are not within specifications.
Repair: The sensor is not producing a valid signal. Replace the suspect throttle 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 connectors.
- Remove the wire from the terminal location for the suspect sensor at the ECM connector:
- P1-66 (#1 throttle position
- P1-1 (#2 throttle position
- Install a 208-0059 Adapter Cable As (70-PIN BREAKOUT) between the J1 and the P1 ECM connectors.
- Connect the J1/P1 ECM connectors.
- Turn the keyswitch to the ON position.
- Measure the frequency between the suspect signal wire (throttle position) and P1-5 (digital return) on the breakout harness while you operate the throttle.
- Set the multimeter to read the duty cycle of the sensor. Measure the duty cycle between the suspect signal wire (throttle position) and P1-5 (digital return) on the breakout harness while you operate the throttle.
- Turn the keyswitch to the OFF position.
Expected Result:
The frequency is between 150 and 1000 Hz. The duty cycle is between 7 percent and 95 percent.
Results:
- OK - The frequency and the duty cycle are within specifications for the entire range of the throttle.
Repair: A valid signal appears at the ECM, but the ECM is not reading the signal properly. There may be a problem with the ECM. Before you consider replacing the ECM, consult the Dealer Solution Network (DSN).
STOP
- Not OK - The frequency and the duty cycle are not within specifications.
Repair: There is a valid signal in the isolated circuit between the sensor and connector, but there is not a valid signal at the ECM connector. The problem is in the harness wiring or in a connector between the ECM and the harness connector for the suspect throttle position sensor. Repair the harness and/or the connectors. Replace parts, if necessary. Verify that the repair eliminates the problem.
STOP