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. All other lamps are optional.
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/P1:28) 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 Engine Control Module (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 1 | g01152462 |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect connector (1). Also inspect the harness for the check engine lamp. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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| Illustration 2 | g01146374 |
Left side engine view (typical example) (1) J1/P1 ECM connectors | |
- 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.
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| Illustration 3 | g01152407 |
P1 connector (28) Check engine lamp (52) +Battery (65) -Battery | |
- Check the allen head screw on the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque value.
- Check the harness and wiring for abrasion and pinch points from the battery to the ECM.
Expected Result:
All connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion or of pinch points.
Results:
- OK - The connectors and wiring appear to be OK. Proceed to Test Step 2.
- Not OK - The connectors and/or wiring are in need of repair.
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 Check Engine Lamp
- Turn the keyswitch to the ON position. Monitor the check engine lamp. The ECM will illuminate the lamp for five seconds.
- Turn the keyswitch to the OFF position.
Expected Result:
The check engine lamp illuminates for five seconds after the keyswitch is turned to the ON position.
Results:
- OK - The check engine lamp is operating normally.
Repair: There may be an intermittent problem with the wiring and/or the connectors. Repair the lamp circuit or send the vehicle to the OEM dealer for repairs.
STOP
- Not OK - The check engine lamp does not turn on. Proceed to Test Step 3.
Test Step 3. Test the Check Engine Lamp Circuit
- Fabricate a jumper wire that can be used to test the circuit. Crimp connector pins to each end of the jumper.
- Disconnect the J1/P1 ECM connectors.
- Insert the jumper into terminal P1-28 (change oil lamp).
- Insert the other end of the jumper wire into terminal P1-52 (-Battery).
- While the lamp is being watched, insert the jumper wire and remove the jumper wire from terminal P1-65.
- Remove the jumper wire from the ECM connector.
Expected Result:
Result 1 The check engine lamp turns on while the jumper is connected. Also, the check engine lamp turns off when the jumper is removed.
Result 2 The check engine lamp does not turn on while the jumper is connected to both sockets.
Result 3 The check engine lamp remains on while the ECM connector is disconnected.
Results:
- Result 1 - The lamp turns on and off when the ECM is bypassed. The circuit for the check engine lamp is OK. Proceed to Test Step 4.
- Result 2 - The check engine lamp does not illuminate when the ECM is bypassed.
Repair: The vehicle's lamp circuit is not functioning properly. The lamp is probably burned out or there is a problem in the lamp circuit from the cab to the ECM. Check if the circuit protection for the vehicle has been tripped. Repair the lamp circuit or send the vehicle to the OEM dealer for repairs.
STOP
- Result 3 - The check engine lamp remains on while the J1/P1 ECM connectors are disconnected.
Repair: 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
- Fabricate a jumper wire with a socket terminal on one end.
- Remove terminal P1-28 (change oil lamp) from the ECM connector. Insert the jumper wire (socket terminal) into P1-28.
- Connect the J1/P1 ECM connector.
- Connect one lead of a test lamp to the jumper wire. Connect the other lead of the test lamp to the positive terminal of the vehicle's battery.
- Turn the keyswitch to the ON position.
- Observe the test lamp. The lamp should turn on for five seconds. The lamp should then turn off.
- Turn the keyswitch to the OFF position.
- Return the wiring to the original configuration.
Expected Result:
The test lamp turns on and the test lamp turns off per the above description.
Results:
- OK - The test lamp illuminated when the keyswitch was turned to the ON position.
Repair: The lamp circuit and the ECM appear to be functioning properly. There may be an intermittent problem. Return the vehicle to service. If the problem persists, retest the circuit or send the vehicle to the OEM dealer for repairs.
STOP
- Not OK - The test lamp did not illuminate when the keyswitch was turned to the ON position.
Repair: Temporarily connect a test ECM. Check the output circuit of the ECM that supplies power to the check engine lamp when the test ECM is installed. If the problem is resolved with the test ECM, reconnect the suspect ECM. If the problem returns with the suspect ECM, replace the ECM.
STOP