Trailer Lamps Malfunction (Without U4G)
Trailer Lamps Malfunction (Without U4G)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructionsprovides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The trailer park lamp relay is supplied with battery voltage at all times. The trailer park lamp signal circuit is grounded by turning the headlamp switch. The body control module (BCM) energizes the trailer park lamp relay by applying ground to the trailer park lamp relay control circuit. When the trailer park lamp relay is energized, the relay switch contacts close and battery voltage is applied through the trailer park lamp relay fuse to the trailer park lamp supply voltage circuit which illuminates the trailer park lamps if a trailer is connected.
Reference Information
Schematic Reference
Trailer Connector/Provision Schematics Trailer Connector/Provision Schematics
Connector End View Reference
Component Connector End Views Connector End Views By Name
Description and Operation
Exterior Lighting Systems Description and Operation Exterior Lighting Systems
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module Referencesfor scan tool information
Circuit/System Verification
1. Ignition ON, observe the function of the left trailer turn signal lamp and the right trailer turn signal lamp while commanding the Left Trailer Turn Signal Lamp and the Right Trailer Turn Signal Lamp ON and OFF with a scan tool. The left trailer turn signal lamp and the right trailer turn signal lamp should turn ON and OFF while changing between the commanded states.
• If the left or right trailer turn signal lamp is always ON or always OFF, refer to Trailer Turn Signal Lamps Malfunction.
2. Observe the function of the trailer tail lamps while commanding the Trailer Park Lamps ON and OFF with a scan tool. The trailer tail lamps should turn ON and OFF while changing between the commanded states.
• If the trailer parks lamps are always ON or always OFF, refer to Trailer Park Lamps Malfunction.
Circuit/System Testing
Trailer Turn Signal Lamps Malfunction
1. Ignition OFF, disconnect the X5 harness connector at the K9 BCM.
2. Ignition ON, test for greater than 10 V between the control circuit terminal listed below and ground:
* Right trailer turn signal lamp control terminal 17
* Left trailer turn signal lamp control terminal 8
• If less than the specified value, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the X50A fuse block-underhood.
3. Connect a 10 A fused jumper wire between the trailer turn signal lamp fused test point and B+. Verify that the appropriate trailer turn signal lamp is illuminated.
• If the trailer turn signal lamp is not illuminated, test the control circuit listed below for a short to ground or an open/high resistance. If the circuit tests normal, replace the X50A fuse block-underhood.
* Control terminal 43 X2 at the X50A fuse block-underhood.
* Control terminal 67 X2 at the X50A fuse block-underhood.
4. If all the circuits test normal, replace the K9 BCM.
Trailer Park Lamps Malfunction
1. Ignition OFF, disconnect the trailer park lamp relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
• If the test lamp illuminates, test the control circuit for a short to voltage
3. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 86 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
4. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the trailer park lamp relay.
5. Connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the trailer park lamps are activated.
• If the trailer park lamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the trailer park lamps.
6. Connect a test lamp between the control circuit terminal 85 and the B+ circuit terminal 86.
7. Command the Trailer Park Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 BCM.
8. If all circuits test normal, test or replace the trailer park lamp relay.
Component Testing
Relay Test
1. Ignition OFF, disconnect the trailer park lamp relay.
2. Test for 60-180 ohm between terminals 85 and 86.
• If not within the specified range, replace the trailer park lamp relay.
3. Test for infinite resistance between the following terminals:
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
• If not the specified value, replace the trailer park lamp relay.
4. Install a 5 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohm between terminals 30 and 87.
• If greater than the specified range, replace the trailer park lamp relay.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)
* Fuse Block Replacement Fuse Block Replacement
* Control Module References Control Module Referencesfor BCM replacement, programming and setup