Use this procedure to troubleshoot the electrical system if a problem is suspected with the circuit that is for the throttle position sensor or if one of the diagnostic codes 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 frequency on the throttle signal or an incorrect duty cycle on the throttle signal. The frequency is below 150 Hz or the frequency in above 1000 Hz. The duty cycle is less than 5 percent or the duty cycle is greater than 95 percent. This code is used when the parameter for the "Desired Speed Input Configuration" is configured to "PWM". |
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 defaults to rated speed. |
| 1690-8 Throttle #2 Position Sensor abnormal frequency, pulse width, or period | The ECM detects an incorrect value for the throttle signal. The value for the analog input is outside the range of zero to five volts. This code is used when the parameter for the "Desired Speed Input Configuration" is configured to "0 - 5 VDC". |
|
The throttle position sensor provides the throttle signal to the engine's ECM. The output for rated speed is a pulse width modulated signal (PWM) at a constant frequency. The throttle position sensor produces a minimum duty cycle in the lowest position and a maximum duty cycle in the highest position of the sensor. When the sensor is in the lowest position, the ECM translates the sensor's output signal to a throttle position of 0 percent. When the sensor is placed in the highest position, the ECM translates the output signal to a throttle position of 100 percent.
The ECM uses an automatic calibration function that allows the ECM to maximize the usable range 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.
This application can also be equipped with a load sharing module. The load sharing module provides a throttle signal to the ECMin place of the throttle position sensor. The output of the load sharing module allows multiple generators to share the load equally. The speed signal from the load sharing module varies with the position of the speed adjust potentiometer. The output signal is expressed as a percentage between 0 and 100 percent for the speed adjust.
The ECM calculates the desired engine rpm from the throttle signal. The throttle signal is valid when the duty cycle is in the range of 5 to 95 percent. If the ECM determines that the throttle signal is invalid, the engine rpm will be set to the programmed rated speed.
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| Illustration 1 | g01385784 |
Schematic for the speed control circuit | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Remove electrical power from the ECM.
- Thoroughly inspect connectors (1) and (2). Also, thoroughly inspect all of the other connectors that are in the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details that are related to inspection of the electrical connectors.
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| Illustration 2 | g01385785 |
Location of the connectors that are for the speed control (rear engine view) (1) J1/P1 ECM connectors (2) Customer connector | |
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the engine interface connector that are associated with the circuit.
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| Illustration 3 | g01385791 |
Terminal locations at the P1 ECM connector that are for the speed control (P1-61) −Battery (P1-66) Primary throttle signal | |
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| Illustration 4 | g01385794 |
Terminal locations at the engine interface connector that are for the speed control (Terminal 2) −Battery (Terminal 4) Secondary throttle signal (Terminal 10) Primary throttle signal | |
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| Illustration 5 | g01366739 |
Terminal locations at the engine interface connector that are for the speed control (Terminal 2) −Battery (Terminal 10) Throttle signal (Terminal 30) Keyswitch | |
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| Illustration 6 | g01159881 |
Terminal locations at the connector for the throttle position sensor (Terminal A) −Battery (Terminal B) Keyswitch (Terminal C) Throttle signal | |
- Check the allen head screw on each ECM connector and the engine interface connector for the proper torque. refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- Check the harness and the wiring for abrasion and for pinch points.
Expected Result:
All 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 connectors and wiring 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.
STOP
Test Step 2. 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 through the entire range of travel.
- Remove electrical power from the ECM.
Expected Result:
The status is zero percent when the throttle is in the lowest position of travel. The status progressively increases to 100 percent when the throttle is in the highest position of travel.
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 an intermittent electrical problem is suspected.
STOP
- Not OK - The throttle position that is displayed on Cat ET does not correspond to the movement of the throttle. Proceed to Test Step 3.
Test Step 3. Check the Supply Voltage at the Sensor
- Disconnect the throttle position sensor at the harness connector.
- Restore electrical power to the ECM.
- Measure the voltage across terminal A (+Battery) and terminal B (−Battery) on the harness side of the connector.
- Remove electrical power from the ECM. Restore the wiring to the original configuration.
Expected Result:
The supply voltage measures 24 ± 2 VDC at the sensor connector for 24 V systems. The supply voltage measures 12 ± 2 VDC at the sensor connector for 12 V systems.
Results:
- OK - The correct voltage is measured at the sensor connector. The sensor is receiving the correct supply voltage. Proceed to Test Step 4.
- Not OK - The voltage is not correct at the sensor connector.
Repair: There is a problem in the keyswitch circuit that is between the ECM and the throttle position sensor. Repair the circuit. Refer to the Schematic for the electrical system for information. If a problem is suspected with the keyswitch circuit that is for the engine, refer to Troubleshooting, "Electrical Power Supply - Test" for details that are related to troubleshooting a problem with the circuit.
STOP
Test Step 4. Check the Signal Frequency and the Duty Cycle at the Sensor
- Disconnect the sensor connector for the throttle position sensor.
- Remove the signal wire from terminal C of the harness side of the connector for the throttle position sensor.
- Install a 7X-6370 Adapter Cable As (3-PIN BREAKOUT) at the sensor connector.
- Connect the sensor to the breakout harness.
- Restore electrical power to the ECM.
- Measure the frequency and the duty cycle between terminal B (−Battery) and terminal C (throttle position) at the 7X-6370 Adapter Cable As (3-PIN BREAKOUT) while you actuate the throttle through the entire range of travel.
- Remove electrical power from the ECM.
- Remove the breakout harness. Restore the wiring to the original configuration.
Expected Result:
The frequency is between 150 and 1000 Hz. The duty cycle is between 5 and 95 percent.
Results:
- OK - The frequency and the duty cycle are within specifications for the entire range of the sensor. The sensor is producing a valid signal. Proceed to Test Step 5.
- Not OK - The frequency and the duty cycle are 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 5. Check the Signal Frequency and the Duty Cycle at the ECM
- Remove the throttle signal wire at terminal location P1-66 from the ECM connector in order to isolate the circuit.
- Restore electrical power to the ECM.
- Install a 7X-1709 Multimeter Probe (BLACK) into terminal location P1-61 (−Battery) of the ECM connector.
Note: Ensure that the multimeter probe is in good repair. A bent probe may contact other terminals inside the connector.
- Measure the duty cycle of the throttle position sensor. Measure the frequency between the loose wire and the multimeter probe at the ECM connector while you actuate the throttle through the entire range of travel.
- Remove electrical power from the ECM.
Expected Result:
The frequency is between 150 and 1000 Hz. The duty cycle is between 5 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 is a problem with the ECM. Perform the following procedure:Replace the ECM. Refer to Troubleshooting, "ECM - Replace" for details.
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