3126B Petroleum Engine Caterpillar

The diagnostic lamp is used to inform the operator of active diagnostic codes and active event codes.

Use this procedure to troubleshoot a suspected problem with the diagnostic lamp or the diagnostic lamp circuit.

The Electronic Control Module (ECM) provides a path to ground for the diagnostic lamp. When the ECM connects the diagnostic lamp to ground the diagnostic lamp will turn on.

Illustration 1	g01123371
Schematic for the diagnostic lamp

Test Step 1. Check the Operation of the Diagnostic Lamp

1. Turn the keyswitch to the ON position.

2. Monitor the diagnostic lamp.

Expected Result:

The diagnostic lamp turns on for five seconds. Then, the diagnostic lamp turns off. If a diagnostic code is active, the diagnostic lamp will flash.

Results:

• OK - The diagnostic lamp turns on for five seconds. Then, the diagnostic lamp turns off. The diagnostic lamp appears to be operating correctly at this time.STOP

• Not OK - The diagnostic lamp did not turn on for five seconds.

  Repair: Replace the light bulb for the diagnostic lamp. Verify that the repair resolved the problem.

  If the repair did not resolve the problem, proceed to Test Step 2.

Test Step 2. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.

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Illustration 2	g01146374
Left side engine view (typical example) (1) J1/P1 ECM connector

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Illustration 3	g01146383
Left side engine view (typical example) (2) P61 Customer connector

2. Thoroughly inspect connectors (1) and (2). Inspect the connections on the diagnostic lamp. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 4	g01102224
P1 terminals that are associated with the diagnostic lamp (P1-28) Diagnostic lamp (P1-65) −Battery

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Illustration 5	g01102219
J61 and P61 terminals that are associated with the diagnostic lamp (24) Diagnostic lamp

3. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the diagnostic lamp.

4. Check the allen head screw for the ECM connectors and the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

5. Check the harness and wiring for abrasions and for pinch points from the diagnostic lamp to the ECM.

Expected Result:

All of the 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 the wiring are OK. Proceed to Test Step 3.

• Not OK - There is a problem with a connector and/or the wiring.

  Repair: Repair the connector 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 problem is resolved.

  STOP

Test Step 3. Test the Diagnostic Lamp Circuit at the ECM Connector

1. Disconnect the J1/P1 connectors.

2. Connect a jumper wire between terminal P1-28 and engine ground.

3. Turn the keyswitch to the ON position and observe the diagnostic lamp.

4. Remove the jumper wire and observe the diagnostic lamp.

Expected Result:

The diagnostic lamp turned on while the jumper wire was connected. The diagnostic lamp turned off when the jumper wire was removed.

Results:

• OK - The diagnostic lamp turned on while the jumper wire was connected. The diagnostic lamp turned off when the jumper wire was removed. The circuit for the diagnostic lamp is functioning properly. Proceed to Test Step 6.

• Not OK - The diagnostic lamp did not turn on. There is a problem with the circuit for the diagnostic lamp. Proceed to Test Step 4.

Test Step 4. Test the Diagnostic Lamp Circuit at the Diagnostic Lamp

1. Disconnect wire F404-RD from the diagnostic lamp.

2. Connect a jumper wire between the diagnostic lamp's open terminal and engine ground.

3. Turn the keyswitch to the ON position and observe the diagnostic lamp.

4. Remove the jumper wire and observe the diagnostic lamp.

Expected Result:

The diagnostic lamp turned on while the jumper wire was connected. The diagnostic lamp turned off when the jumper wire was removed.

Results:

• OK - The diagnostic lamp turned on while the jumper wire was connected. The diagnostic lamp turned off when the jumper wire was removed. The +Battery side of the circuit for the diagnostic lamp is functioning properly. There is a problem with the return wire between the diagnostic lamp and the P1 connector.

  Repair: Repair wire F404-RD between the diagnostic lamp and P1-28. Verify that the problem is resolved.

  STOP

• Not OK - The diagnostic lamp did not turn on when the jumper wire was connected. There is a problem with the +Battery side of the circuit for the diagnostic lamp. Proceed to Test Step 5.

Test Step 5. Check the Voltage from the Keyswitch to the Diagnostic Lamp

1. Turn the keyswitch to the OFF position.

2. Remove the wire from the terminal R of the keyswitch.

3. Turn the keyswitch to the ON position.

4. Measure the voltage on terminal B of the keyswitch to engine ground.

5. Measure the voltage on terminal R of the keyswitch to engine ground.

6. Turn the keyswitch to the OFF position.

Expected Result:

Voltage is present on terminal B and terminal R at the keyswitch.

Results:

• OK - Voltage is present on terminal B and terminal R at the keyswitch.

  Repair: If voltage is present on terminal R, repair the wire between the keyswitch and the diagnostic lamp. Verify that the breaker is not tripped. Return all wiring to the original configuration. Verify that the problem is resolved.

  STOP

• Not OK - Voltage is not present on terminal B at the keyswitch.

  Repair: If voltage is not present on terminal B, repair the wire between the +Battery and the keyswitch. Check the battery's no-load voltage. Return all wiring to the original configuration. Verify that the problem is resolved.

  STOP

• Not OK - Voltage is not present on terminal R at the keyswitch.

  Repair: If voltage is present on terminal B of the keyswitch but not present on terminal R, replace the keyswitch. Return all wiring to the original configuration. Verify that the problem is resolved.

  STOP

Test Step 6. Check the Operation of the ECM

1. Remove terminal P1-28.

2. Fabricate a jumper wire for the ECM connector.

3. Insert the jumper into P1-28.

4. Connect the J1/P1 connectors.

5. Connect one probe of a voltage test lamp to the jumper wire in P1-28.

6. Connect the other probe of the voltage test lamp to +Battery.

7. Turn the keyswitch to the ON position. Wait for ten seconds.

8. Turn the keyswitch to the OFF position.

Expected Result:

The test lamp turned ON for five seconds. Then, the test lamp turned OFF.

Results:

• OK - The test lamp turned ON for five seconds. Then, the test lamp turned OFF. The ECM is operating correctly. The problem appears to be resolved.

  Repair: The problem may be intermittent. If the problem is intermittent, refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The test lamp did not turn on for five seconds. There is a problem with the ECM.

  Repair: Temporarily connect a test ECM. Refer to Troubleshooting, "Replacing the ECM". Check the operation of the diagnostic lamp when the test ECM is installed.If the problem is resolved with the test ECM, connect the suspect ECM. If the problem returns with the suspect ECM, replace the ECM. Verify that the problem is resolved.

  STOP