3516B Engine for 994F and 994H Wheel Loaders Caterpillar

Use this procedure to troubleshoot the electrical system if the diagnostic code in Table 1 is active or easily repeated.

Depressing the right brake pedal will disable the throttle lock feature. The previous engine rpm that was set may be resumed by pressing the "Resume/Accel Switch".

The throttle lock feature eliminates fatigue from holding the throttle pedal down for extended periods of time. The throttle lock feature allows the operator to maintain a desired engine rpm without the use of the throttle pedal.

The engine Electronic Control Module (ECM) will disable the throttle lock feature if the signals from the right brake switch are invalid. The throttle lock feature will remain disabled until the keyswitch is cycled from the OFF position to the ON position.

Illustration 1	g02595756
Typical schematic

Test Step 1. Check for Connector Damage.

1. Turn the keyswitch to the OFF position.

2. Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the other connectors. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.

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Illustration 2	g01150093
P1 ECM connector (P1-21) Right brake (NO) (P1-22) Right brake (NC) (P1-5) Digital return

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

4. Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

5. Check the harness and the wiring for abrasion and for pinch points.

Expected Result:

The connectors and wiring are free of the following problems: damage, corrosion, abrasion and incorrect attachment.

Results:

• OK - The connectors and wiring are okay. Proceed to test step 2.

• Not OK - The connectors and/or wiring are not okay.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

Test Step 2. Check the Right Brake Switch on the Caterpillar Electronic Technician (ET).

1. Install the Cat ET.

2. Turn the keyswitch to the ON position. The engine is OFF.

3. Operate the right brake switch.

4. Observe the status of the right brake switch on the Cat ET.

Expected Result:

The right brake switch status is "ON" when the right brake pedal is depressed. The right brake switch status is "OFF" when the right brake pedal is released.

Results:

• OK - The switch and wiring are OK.

  Repair: If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The status of the right brake switch is incorrect on the Cat ET. Proceed to test step 3.

Test Step 3. Short the Wires at the Right Brake Switch.

1. Disconnect the connector for the right brake pedal switch at the switch.

2. Install a jumper wire across terminal A and terminal B on the harness side of the connector for the right brake pedal switch.

3. Turn the keyswitch to the OFF position.

4. Turn the keyswitch to the ON position. The engine is OFF.

5. Observe the status of the right brake switch on the Cat ET.

6. Remove the jumper wire.

7. Install a jumper wire across terminal A and terminal C of the harness side of the connector for the right brake pedal switch.

8. Turn the keyswitch to the OFF position.

9. Turn the keyswitch to the ON position. The engine is OFF.

10. Observe the status of the right brake switch on the Cat ET.

11. Remove the jumper wire.

Expected Result:

The right brake switch status is "OFF" when terminal A (digital return) and terminal B (right brake pedal switch (N/C)) are shorted together.

The right brake switch status is "ON" when terminal A (digital return) and terminal C (right brake pedal switch (N/O)) are shorted together.

Results:

• OK - The ECM read the signal from the right brake switch correctly. The harness and the ECM are okay.

  Repair: Temporarily connect a new right brake switch. Verify that the new right brake switch solves the problem before permanently installing the new right brake switch.

  STOP

• Not OK - The ECM did not read the signal from the right brake switch correctly. There is a problem in the harness or the ECM. Proceed to test step 4.

Test Step 4. Check for a Short Circuit in the Wiring Harness.

1. Turn the keyswitch to the OFF position.

2. Turn the circuit breaker for the engine to the OFF position.

3. Disconnect ECM connector J1/P1.

4. Set a multimeter on the 20,000 Ohm position.

5. Measure the resistance between P1-21 and P1-5.

6. Measure the resistance between P1-21 and P1-22.

7. Measure the resistance between P1-22 and P1-5.

8. Measure the resistance between P1-22 and the engine ground.

9. Measure the resistance between P1-21 and the engine ground.

Expected Result:

The resistance is greater than 20,000 Ohms.

Results:

• OK - The resistance is greater than 20,000 Ohms. Proceed to test step 5.

• Not OK - The resistance is less than 20,000 Ohms. There is a short in the harness between the right brake switch and the ECM.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

Test Step 5. Check the Resistance through the Harness.

1. Install a jumper wire across terminal A and terminal C of the harness side of the connector for the right brake pedal switch.

2. Set the multimeter on the 200 Ohm position.

3. Measure the resistance between P1-21 and P1-5.

4. Remove the jumper wire.

5. Install a jumper wire across terminal A and terminal B on the harness side of the connector for the right brake pedal switch.

6. Measure the resistance between P1-22 and P1-5.

7. Remove the jumper wire.

Expected Result:

The resistance is less than ten Ohms for each measurement.

Results:

• OK - The resistance is less than ten Ohms for each measurement. Proceed to test step 6.

• Not OK - The resistance is greater than ten Ohms for each measurement. There is an open or excessive resistance in the harness.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

Test Step 6. Short the Wires of the Right Brake Switch at the ECM.

1. Remove the wires from P1-21, P1-22 and P1-5 at the ECM connector P1.

2. Insert a wire with a socket terminal at each end into ECM connector P1-22 and P1-5.

3. Reconnect all connectors.

4. Turn the keyswitch to the ON position. The engine is OFF.

   Note: Additional diagnostic codes will be generated because the digital return will no longer be connected to other sensors and switches. Ignore the codes and clear the codes when you have completed this test.

5. Observe the status of the right brake switch on the Cat ET.

6. Turn the keyswitch to the OFF position.

7. Disconnect J1/P1 and remove the wire short.

8. Insert a wire with socket terminals at each end into ECM connector P1-21 and P1-5.

9. Reconnect all the connectors.

10. Turn the keyswitch to the ON position. The engine is OFF.

11. Observe the status of the right brake switch on the Cat ET.

12. Turn the keyswitch to the OFF position.

13. Remove the wire short.

14. Replace all wiring. Reconnect all connectors.

Expected Result:

The status of the right brake switch is "OFF" when the wire short is inserted between P1-22 and P1-5.

The status of the right brake switch is "ON" when the wire short is inserted between P1-21 and P1-5.

Results:

• OK - The ECM reads the correct signal when the jumper is at P1 but not at the right brake switch. The harness is faulty.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

• Not OK - The correct signal for the right brake switch appears at P1. The ECM is not reading the signal for the right brake switch properly.

  Repair: Replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP