Headlamps Malfunction (With T4Q)
Headlamps Malfunction (With T4Q)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (with HP2) (Initial Inspection and Diagnostic Overview)Diagnostic System Check - Vehicle (without HP2) (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G200. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil is supplied with ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to the relay coil and switch circuits. The low beam headlamps operate when the BCM grounds the relay coil control circuit to the relay coil of the low beam headlamp relay. This energizes the low beam relay causing the switch contacts to close. With the switch contacts closed, battery voltage is applied to the LT LO and RT LO beam fuses through to the left and right light emitting diode (LED) control modules. When the headlamp high beam relay coil is energized, current flows through the LT HI BEAM and the RT HI BEAM fuses to the left and right LED control modules. With the headlamp dimmer switch in the high beam position the BCM sends a serial data message to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator.
Diagnostic Aids
The headlamp outage detection circuits are low current B+ circuits supplied by the BCM. For purposes of testing, a test lamp connected between the outage detection circuit and ground will not illuminate due to low current.
Reference Information
Schematic Reference
* Headlights/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) Schematics)
* Exterior Lights Schematics (Exterior Lights Schematics)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Ignition ON, observe the scan tool Headlamp Switch parameter while turning the headlamp switch ON and OFF. The reading should toggle between Active and Inactive.
• If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.
2. Observe the scan tool Flash to Pass Switch parameter while applying and releasing the flash to pass switch. The reading should toggle between Active and Inactive.
• If the reading does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.
3. Observe the scan tool High Beam Select Switch parameter while applying and releasing the high beam select switch. The reading should toggle between Active and Inactive.
• If the reading does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.
4. Command the Low Beams ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when commanded.
• If the low beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction -Low Beam.
5. Command the High Beams ON and OFF with a scan tool. The high beam headlamps should turn ON and OFF when commanded.
• If the high beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction -High Beam.
6. Command the High Beams ON and OFF with a scan tool. The High Beam Indicators should turn ON and OFF.
• If the High Beam Indicators do not turn ON and OFF, refer to High Beam Indicators Malfunction.
7. Observe the low beam, high beam, park, and marker lamp LEDs at each headlamp assembly. ALL LEDs should illuminate when commanded ON.
• If ALL LEDs illuminate when commanded and the Service Headlamp Assembly indicator is ON, refer to Headlamp Outage Detection Malfunction.
Circuit/System Testing
Headlamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the Headlamp and Panel Dimmer Switch.
2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal 8.
• If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool Headlamp Switch parameter is Inactive.
• If not the specified value, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the BCM.
4. Verify the scan tool Auto Hdlp. Disable Sw. parameter is Inactive.
• If not the specified value, test the signal circuit terminal 3 for a short to ground. If the circuit tests normal, replace the BCM.
5. Install a 3A fused jumper wire between the signal circuit terminal 1 and ground. Verify the scan tool Headlamp Switch parameter is Active.
• If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
6. Install a 3A fused jumper wire between the signal circuit terminal 3 and ground. Verify the scan tool Auto Hdlp. Disable Sw. parameter is Active.
• If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.
7. If all circuits test normal, test or replace the Headlamp and Panel Dimmer Switch.
Turn Signal/Multifunction Switch Malfunction
1. Ignition OFF, disconnect the X2 harness connector at the turn signal/multifunction switch.
2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal D.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool Flash to Pass Switch parameter is Inactive.
• If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the BCM.
4. Verify the scan tool High Beam Select Switch parameter is Inactive.
• If not the specified value, test the signal circuit terminal E for a short to ground. If the circuit tests normal, replace the BCM.
5. Install a 3A fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Flash to Pass Switch parameter is Active.
• If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
6. Install a 3A fused jumper wire between the signal circuit terminal E and ground. Verify the scan tool High Beam Select Switch parameter is Active.
• If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
7. If all circuits test normal, test or replace the turn signal/multifunction switch.
Headlamps Malfunction - Low Beam
1. Ignition OFF, disconnect the HDLP LO/HID 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. Verify that 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.
4. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
5. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
6. Command the Low Beams 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 ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
• 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 BCM.
7. Ignition OFF, connect the HDLP LO/HID relay.
8. Disconnect the harness connector at the inoperative headlamp.
9. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohms between each ground circuit terminal listed below and ground.
* Ground circuit terminal F
* Ground circuit terminal M
• If greater than the specified range, test the ground circuit for an open/high resistance.
10. Connect a test lamp between the control circuit terminal A and ground.
11. Command the Low Beams 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 ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the HDLP LO/HID relay.
• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HDLP LO/HID relay.
12. Ignition OFF, connect the harness connector at the inoperative headlamp.
13. Command the Low Beams ON and OFF with a scan tool. The low beam headlamp should turn ON and OFF when changing between the commanded states.
• If all of the low beam LED's do not illuminate, replace the appropriate headlamp control module.
• If some of the low beam LEDs illuminate, replace the appropriate headlamp assembly.
Headlamps Malfunction - High Beam
1. Ignition OFF, disconnect the X4 connector at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal C3 and B+.
3. Ignition ON, command the High Beams 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 ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
• 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 BCM.
4. Ignition OFF, disconnect the harness connector at the inoperative headlamp.
5. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohms between each ground circuit terminal listed below and ground.
* Ground circuit terminal F
* Ground circuit terminal M
• If greater than the specified range, test the ground circuit for an open/high resistance.
6. Connect a test lamp between the control circuit terminal L and ground.
7. Command the High Beams 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 ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.
• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
8. Ignition OFF, connect the harness connector at the inoperative headlamp.
9. Command the High Beams ON and OFF with a scan tool. The high beam headlamp should turn ON and OFF when changing between the commanded states.
• If all of the high beam LED's do not illuminate, replace the appropriate headlamp control module.
• If some of the high beam LEDs illuminate, replace the appropriate headlamp assembly.
Headlamp Outage Detection Malfunction
1. Ignition OFF, disconnect the harness connector at the appropriate headlamp assembly.
2. Ignition ON, test for B+ between the signal circuit terminal C and ground.
• If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
3. Ignition ON, verify that a test lamp does not illuminate between the signal circuit terminal C and ground.
• If the test lamp illuminates, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
4. If all circuits test normal, test or replace the appropriate headlamp control module.
High Beam Indicator Malfunction
Ignition ON, with a scan tool perform the Display Test for the instrument panel cluster (IPC) and observe the high beam indicator.
If the high beam indicator illuminates during the test, replace the BCM.
If the high beam indicator does not illuminate during the test or remains illuminated at all times, replace the IPC.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
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* Headlamp Switch Replacement (Cadillac) (Service and Repair)Headlamp Switch Replacement (Except Cadillac) (Service and Repair)
* Turn Signal Multifunction Switch Replacement (Turn Signal Multifunction Switch Replacement)
* Control Module References (Programming and Relearning) for BCM or Headlamp Control Module replacement, setup, and programming