3126B Engine for Lexion 450, Lexion 460, and Lexion 460 R Combines Caterpillar

Use this procedure to determine if the circuit for the diagnostic enable switch is operating correctly.

The diagnostic enable switch is used to prompt diagnostic flash codes on the check engine lamp. When the diagnostic enable switch is closed, P1:44 is connected to ground. The Electronic Control Module (ECM) will then flash any active diagnostic codes. The flash codes are two-digit numbers that represent the diagnostic codes.

The flash code is determined by the blinking of the check engine lamp. The lamp will blink for the first digit of the flash code, and the lamp will pause for one second. Then, the lamp will blink for the second digit.

The check engine lamp is located on the diagnostic enable switch. The diagnostic enable switch is located in the electrical panel near the bottom of the panel.

Note: The check engine lamp should not continuously flash the diagnostic flash codes. If the diagnostic enable switch has not been used, then the circuit is probably shorted to ground.

Illustration 1	g00700625
Schematic

Test Step 1. Check the Electrical Connectors and the Wiring

1. Thoroughly inspect the J1/P1 ECM connector, the connection at the switch, and any other connectors in the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

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

3. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

4. Check the harness and wiring for abrasion and pinch points from the diagnostic enable switch back to the ECM.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring should be free of corrosion, abrasion or pinch points.

Results:

• OK - Proceed to Test Step 2.

• Not OK - Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem. Stop.

Test Step 2. Test the Check Engine Lamp

1. Ensure that the diagnostic enable switch is in the OFF position.

2. Turn the keyswitch to the ON position. Do not start the engine. Observe the check engine lamp.

Expected Result:

The lamp should turn on for five seconds. Then, the lamp should turn off. The lamp will remain on if there is an active diagnostic code.

Results:

• OK - The check engine lamp circuit is working properly at this time. Proceed to Test Step 3.

• Not OK - The check engine lamp is not working properly.

  Repair: Repair the lamp circuit. Refer to Troubleshooting, "Check Engine Lamp Circuit - Test".

  Stop.

Test Step 3. Test the Diagnostic Enable Switch

1. Turn the keyswitch to the ON position.

2. Activate the diagnostic enable switch and observe the check engine lamp.

3. Deactivate the diagnostic enable switch and observe the check engine lamp.

Expected Result:

When the diagnostic enable switch is activated, the check engine lamp should flash out flash code 55 (No Diagnostic Codes Detected) or the flash code for any active diagnostic codes. When the diagnostic enable switch is deactivated, the check engine lamp should not flash.

Results:

• OK - The check engine lamp flashes only when the diagnostic enable switch is activated. The diagnostic enable switch is operating properly at this time.

  Repair: If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".

  Stop.

• No Flash - The check engine lamp does not flash regardless of the position of the diagnostic enable switch. Proceed to Test Step 4.

• Flashes Continuously - The check engine lamp flashes regardless of the position of the diagnostic enable switch. Proceed to Test Step 6.

Test Step 4. Short the Wires at the Switch

1. Turn the keyswitch to the OFF/RESET position.

2. Disconnect the wires from the diagnostic enable switch. Record the placement of the wires so the wires can be reconnected to the proper terminals.

3. Use a jumper wire to short the two wires that were removed from the diagnostic enable switch.

4. Turn the keyswitch to the ON position. Do not start the engine.

5. Observe the check engine lamp. The check engine lamp should flash.

6. Turn the keyswitch to the OFF/RESET position.

7. Remove the jumper wire.

Expected Result:

The check engine lamp flashes when the jumper wire is installed in the circuit.

Results:

• OK - The ECM is working properly and there is no problem with the harness.

  Repair: Temporarily replace the diagnostic enable switch. Verify that the replacement eliminates the problem before permanently installing the new switch.

  Stop.

• Not OK - The check engine lamp does not flash when the jumper wire is installed. Proceed to Test Step 5.

Test Step 5. Short the Circuit at the ECM

Illustration 2	g00989641
ECM connector P1 (wire side)

1. Turn the keyswitch to the OFF/RESET position.

2. Remove the wire from P1:44 (Diagnostic Enable Switch).

3. Install a jumper wire with a Deutsch socket on one end and an alligator clip on the other end between P1:44 (Diagnostic Enable Switch) and chassis ground.

4. Turn the keyswitch to the ON position. Do not start the engine.

5. Observe the check engine lamp.

6. Turn the keyswitch to the OFF/RESET position.

7. Remove the jumper wire and reconnect the original wire to P1:44 (Diagnostic Enable Switch).

Expected Result:

The check engine lamp flashes when the jumper wire is installed.

Results:

• OK - There is an open circuit in the wiring harness between the ECM and the diagnostic enable switch or between the switch and ground.

  Repair: Locate the open and repair the circuit.Verify that the repair eliminates the problem.

  Stop.

• Not OK - The ECM is not responding to the input.

  Repair: Verify your results. Ensure that P1:44 was connected to a good ground source before you replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  Stop.

Test Step 6. Disconnect the Switch

1. Turn the keyswitch to the OFF/RESET position.

2. Disconnect the wires from the diagnostic enable switch. Record the placement of the wires so the wires can be reconnected to the proper terminals.

3. Turn the keyswitch to the ON position. Do not start the engine.

4. Observe the check engine lamp. The check engine lamp should not flash.

5. Turn the keyswitch to the OFF/RESET position.

Expected Result:

The check engine lamp does not flash when the wires are disconnected from the switch.

Results:

• OK - The switch is bad.

  Repair: Replace the diagnostic enable switch.Verify that the repair eliminates the problem.

  Stop.

• Not OK - The check engine lamp continues to flash when the wires are disconnected from the switch.

  Repair: Reconnect the wires to the switch.

  Proceed to Test Step 7.

Test Step 7. Create an Open at the ECM

Illustration 3	g00989641
ECM connector P1 (wire side)

1. Turn the keyswitch to the OFF/RESET position.

2. Remove the wire from P1:44 (Diagnostic Enable Switch).

3. Turn the keyswitch to the ON position. Do not start the engine.

4. Observe the check engine lamp. The check engine lamp should not flash.

5. Turn the keyswitch to the OFF/RESET position.

6. Reconnect the wire to P1:44 (Diagnostic Enable Switch).

Expected Result:

The check engine lamp does not flash when the wire is disconnected from the ECM.

Results:

• OK - The check engine lamp does not flash. There is a short circuit in the wiring between the ECM and the diagnostic enable switch.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  Stop.

• Not OK - The check engine lamp continues to flash. The ECM is not responding properly.

  Repair: Verify your results before you replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  Stop.