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3126E On-highway Engine Caterpillar


Check Engine Lamp Circuit - Test

Usage:

3126E HEP
System Operation Description:

Use this procedure under the following situation:

Use the following information in order to determine if the check engine lamp is operating incorrectly:

The check engine lamp is the only standard lamp that is used.

The following background information is related to the following procedure:

Check Engine Lamp

The check engine lamp is used to provide the following functions:

  • Indicate the existence of an active diagnostic code.

  • Indicate driver alert status of the Idle Shutdown Timer.

  • Read diagnostic flash codes.

Power Up Lamp Check

At powerup, the lamp will turn ON for five seconds. The lamp will continue to flash if there is an active diagnostic code.

Operation with an Active Diagnostic Code

While the engine is operating, the lamp will turn on for a minimum of five seconds when certain fault conditions exist. If certain fault conditions exist, the lamp will operate in the following manner:

  • The check engine lamp will turn on for five seconds.

  • The check engine lamp will turn off for a short time.

  • The check engine lamp will turn on for another five seconds.

The check engine lamp will continue to operate in this manner while the fault condition exists.

Indication of the Driver Alert Status of the Idle Shutdown Timer

During the final 90 seconds of the operation of the Idle Shutdown Timer, the check engine lamp will begin to flash. The flashing of the check engine lamp indicates that an engine shutdown is near.

Flashing Out Diagnostic Flash Codes

The flash codes are two-digit representations of diagnostic codes. The PID-FMI Diagnostic Code should be used for troubleshooting. The PID is the Parameter Identifier. The FMI is the Failure Mode Identifier. A 110-03 is an example of a PID-FMI Diagnostic Code. Flash codes provide an indication of a failure. Flash codes are not as specific as diagnostic codes. Flash codes only indicate that a failure has occurred. Flash codes do not indicate the specific type of failure. For example, the flash code (27) is used for a 110-03 fault code and a 110-04 fault code. Flash codes should not be used for troubleshooting.

Diagnostic flash codes that are active can be viewed at any time. Turn the Cruise Control On/Off switch to the OFF position. Hold the Set/Resume switch in either the SET position or the RESUME position until the lamp begins to flash. Then release the Set/Resume switch.

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 five seconds. Then, the lamp will blink for the second digit.

Some vehicles are equipped with a diagnostic enable switch. The diagnostic enable switch is used to flash the diagnostic codes by grounding the input of the diagnostic enable switch from terminal 46 to terminal 5 (sensor common). The customer parameter "Diagnostic Enable" must be programmed to "J1/P1:46" to use terminal 46 as an input for a diagnostic enable switch. A switch does not need to be connected to an ECM input in order to be used as a diagnostic enable switch. The switch position is transmitted over the J1939 data link to the ECM. When the ECM receives the message over the J1939 data link, the output (J1/P2:28) will illuminate the check engine lamp. The customer parameter "Diagnostic Enable" must be programmed to "J1939 Body Controller", "J1939 Cab Controller", or "J1939 Instrument Cluster" in order to use a J1939 data link communication to control the check engine lamp. If a problem is suspected with the J1939 data link, refer to Troubleshooting, "Powertrain Data Link Circuit - Test".

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

Electrical Connection of the Check Engine Lamp

One terminal of the check engine lamp must be connected to battery voltage through the vehicle wiring. The other terminal is connected to the ECM at the vehicle harness connector J1/P1:28 (check engine lamp).

The ECM provides a path to ground in order to turn the lamp ON.

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Illustration 1g00676880

Schematic for Lamp

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Illustration 2g00858740

Terminal locations for ECM connector P1

Test Step 1. Inspect Electrical Connectors and Wiring

  1. Thoroughly inspect ECM vehicle harness connector J1/P1, the firewall bulkhead connector, and the check engine lamp (terminal 28). Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

  1. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the check engine lamp.

    Refer to Illustration 2.

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

  1. Check the harness and wiring for abrasion and pinch points from the battery to the ECM.

Expected Result:

All connectors, pins and sockets should be 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: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.

    STOP

Test Step 2. Check for Normal Operation of the Lamp

  1. Monitor the check engine lamp.

    1. Turn the ignition key switch to the ON position. The lamp should illuminate for five seconds. Then, the lamp should turn off.

    1. The lamp will continue flashing if there is an active diagnostic code. If there is an active diagnostic code, connect Caterpillar Electronic Technician (Cat ET) in order to read the active diagnostic code. Troubleshoot the problem.

Expected Result:

The check engine lamp turns on and the check engine lamp turns off per the above description.

Results:

  • Yes - The check engine lamp appears to operating correctly at this time.STOP

  • No - Proceed to Test Step 3.

Test Step 3. Test the Lamp Circuit

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Illustration 3g00858796

P1 Connector

  1. Disconnect ECM vehicle harness connector J1/P1.

  1. Fabricate a jumper wire 100 mm (4 inch) long. Crimp a Deutsch pin to both ends of the wire.

  1. Insert the jumper into P1:28 (check engine lamp).

  1. Connect the other side of the jumper wire to P1:65 (-battery).

  1. Turn the ignition key switch to the ON position.

  1. While the lamp is being watched, insert the jumper wire and remove the jumper wire.

    Refer to Illustration 3.

Expected Result:

Result 1 The check engine lamp turns on while the jumper is connected to both sockets. Also, the check engine lamp turns off when the jumper is removed from one of the sockets.

Result 2 The check engine lamp does not turn on while the jumper is connected to both sockets.

Result 3 The lamp will stay on while the ECM vehicle harness connector is disconnected.

Results:

  • Result 1 - The check engine lamp circuit is functioning properly. Proceed to Test Step 4.

  • Result 2 - The lamp did not turn on. The vehicle's lamp circuit is not functioning properly. The lamp is probably burned out or there is a problem in the wiring from the cab to either the ECM or the +Battery connection. Repair the lamp circuit or send the vehicle to the OEM dealer for repairs.STOP

  • Result 3 -

    Repair: Perform the following diagnostic procedure:The circuit between the ECM and the lamp is shorted to chassis ground. Repair the circuit or send the vehicle to the OEM dealer for repairs.

    STOP

Test Step 4. Check the Operation of the ECM Output for the Check Engine Lamp

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Illustration 4g00858800

ECM Breakout T-connector

  1. Disconnect ECM vehicle harness connector J1/P1.

  1. Insert a breakout T between ECM vehicle harness connector J1 and ECM vehicle harness connector P1.

  1. Connect a probe for the voltage test lamp to P1:65 (-battery) and connect the other probe to P1:52 (unswitched +battery) of the breakout T.

  1. The test lamp should turn on. If the test lamp does not turn on, either the test lamp is faulty or the wiring to the ECM is faulty. Continue with this step if the lamp turns on.

  1. Leave the probe for the voltage test lamp connected to P1:52 (unswitched +battery).

  1. Connect the other probe of the test lamp to P1: 28 (check engine lamp) of the breakout T.

    Refer to Illustration 4.

  1. Watch the voltage test lamp. Turn the ignition key switch to the ON position.

  1. The lamp should turn on for five seconds. Then, the lamp should turn off. The lamp will continue flashing if there is an active diagnostic code. If there is an active diagnostic code, connect Cat ET in order to read the active diagnostic code. Troubleshoot the problem.

Expected Result:

The check engine lamp turns on and the check engine lamp turns off per the above description.

Results:

  • Yes - The ECM is operating correctly. There is a problem in the vehicle wiring or the lamp. Repair the vehicle wiring or the lamp, as required.STOP

  • No - Temporarily connect a test ECM. Check the operation of the check engine lamp when the test ECM is installed. If the problem is resolved with the test ECM, then reconnect the suspect ECM. If the problem returns with the suspect ECM, then replace the ECM.STOP

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