Use this procedure to troubleshoot any suspect problems with the circuit for the throttle switch.
Use this procedure to troubleshoot an active 91-02 Incorrect Throttle Switch inputs.
The throttle switch provides the operator with the ability to select the desired engine speed. The throttle switch is a three-position momentary rocker switch. The three positions are Neutral, Rabbit, and Tortoise. The throttle switch can be used to select high idle or low idle. The throttle switch can also be used to adjust the engine speed in increments.
High Idle - To increase engine speed to high idle, push the top of the switch (Rabbit) one time and release the switch.
Low Idle - To decrease engine speed to low idle, push the bottom of the switch (Tortoise) one time and release the switch.
Increase Engine Speed - To increase engine speed in increments, push the top of the switch (Rabbit) and hold the switch until the proper engine speed is achieved. The desired engine speed will increase from the current engine speed at a rate of 200 rpm per second.
Decrease Engine Speed - To decrease engine speed in increments, push the bottom of the switch (Tortoise) and hold the switch until the proper engine speed is achieved. The desired engine speed will decrease from the current engine speed at a rate of 200 rpm per second.
The throttle switch is connected to the four throttle inputs of the Electronic Control Module (ECM). Each position generates a specific on/off pattern on the throttle inputs. A diagnostic code is generated if a pattern that does not correspond with any of the switch positions is detected.
Once a diagnostic code is generated, the ECM ignores the throttle input signals and the desired engine speed is set to 1000 rpm, unless the actual engine speed is below 1000 rpm. If the actual engine speed is below 1000 rpm, the desired engine speed is set to the current engine speed.
Voltage at the throttle inputs to the ECM is 7.5 ± 0.5 VDC when the throttle inputs are open. The voltage is less than 0.5 VDC when the throttle inputs are closed.
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| Illustration 1 | g03858750 |
Schematic for the throttle inputs | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect the J1/P1 ECM connector and the connector for the throttle switch. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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| Illustration 2 | g01183529 |
Location of the J1/P1 ECM connector (typical left side engine view) | |
- Perform a 45 N (10 lb) pull test on each of the wires in the connectors that are associated with the circuit.
- Check the torque of the allen head screws for each of the ECM connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- Check the harness and wiring for corrosion, for abrasion, and for pinch points 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:
- Not OK - There is a problem with the wiring and/or the connectors.
Repair: Repair the connectors and/or the wiring. Replace parts, if necessary. 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. Check the Status of the Throttle Inputs
- Turn the keyswitch to the OFF position.
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector.
- Turn the keyswitch to the ON position.
- Observe the status of the throttle inputs on Cat ET while you operate the throttle switch in each position.
Show/hide table
Table 1 Throttle Input Neutral High "Rabbit" Low "Tortoise" "#1 (Low)" Off Off On "#2 (Low Par)" On Off On "#3 (High)" Off On Off "#4 (High Par)" On On Off
Expected Result:
The status of the throttle switch corresponds with the table above.
Results:
- OK - The throttle switch is functioning properly at this time.
Repair: The problem appears to be resolved. The problem is probably related to a faulty connection in the harness or at a connector. Carefully inspect the connectors and the wiring that is related to the start circuit. Ensure that all connections are tight and ensure that all wires are crimped correctly. Refer to Troubleshooting, "Electrical Connectors - Inspect" for information that relates to the proper troubleshooting of intermittent electrical problems.
STOP
- Not OK - One or more of the throttle switch inputs are incorrect. Record the suspect input. Proceed to Test Step 3.
Test Step 3. Short the Wires at the Throttle Switch
- Turn the keyswitch to the OFF position.
- Disconnect the connector for the throttle switch.
- Observe the status of the suspect throttle input on Cat ET.
- Fabricate a jumper wire that is long enough to connect across two terminals of the connector for the throttle switch. Crimp a connector pin to each end of the jumper wire.
- Use the jumper wire to short terminal 1 (digital return) to the terminal for the suspect throttle input on the harness side of the connector for the throttle switch.
- Observe the status of the suspect throttle input on Cat ET.
- Remove the jumper wire.
Expected Result:
The correct status of the suspect throttle input is "Off" when the connector for the throttle switch is disconnected. The correct status is "On" when the jumper wire is installed.
Results:
- OK - The harness and the ECM are OK.
Repair: The problem is in the throttle switch. Replace the throttle switch. Verify that the repair eliminates the problem.
STOP
- Not OK - The switch status does not change when the jumper wire is installed. The problem appears to be in the harness or in the ECM. Proceed to Test Step 4.
Test Step 4. Short the Wires at the ECM
- Ensure that the keyswitch is in the OFF position.
- Disconnect the J1/P1 ECM connectors.
- Fabricate a jumper wire that is long enough to connect across the terminals at the ECM connector. Crimp connector sockets to each end of the jumper wire.
- Remove terminal P1-5 (return) and the terminal of the suspect throttle input from the ECM connector. Install the jumper wire into these terminal locations.
- Connect the J1/P1 ECM connectors.
- Turn the keyswitch to the ON position.
- Observe the status of the suspect throttle input on Cat ET.
- Turn the keyswitch to the OFF position.
- Disconnect the J1/P1 ECM connector and remove the jumper wire. Connect the J1/P1 ECM connectors.
- Turn the keyswitch to the ON position.
- Observe the status of the suspect throttle input on Cat ET.
Expected Result:
The correct status of the suspect throttle input is "On" when the jumper wire is installed. The status is "Off" when the jumper wire is removed.
Results:
- OK - The status of the throttle input is correct.
Repair: There is a problem in the harness wiring between the ECM and the throttle switch. Repair the harness. Replace the harness, if necessary. Verify that the repair eliminates the problem.
STOP
- Not OK - The status of the throttle input is not correct.
Repair: The ECM is not responding to the switch inputs. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM" for information that relates to replacement of the ECM.
STOP