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Headlamps Malfunction (With X88, Z75, and Z88)




Headlamps Malfunction (With X88, Z75, and Z88)

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 Instructions 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. 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 low beam headlamps. When the headlamp high beam relay coil is energized, current flows through the LT HI BEAM and the RT HI BEAM fuses to the high beam headlamps. 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.

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
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 References 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 change between Active and Inactive.

• If the reading does not change between the specified values, refer to Headlamp Switch Malfunction.

2. Observe the scan tool Auto Hdlp. Disable Sw. 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 specified values, refer to Headlamp Switch Malfunction.

3. Observe the scan tool Flash to Pass Switch parameter while applying and releasing the turn signal/multifunction switch. The reading should toggle between Active and Inactive.

• If the reading does not change between the specified values, refer to Turn Signal/Multifunction Switch Malfunction.

4. 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 specified values, refer to Turn Signal/Multifunction Switch Malfunction.

5. 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.

6. Command the DRLs ON and OFF with a scan tool. The daytime running lamps should turn ON and OFF when commanded.

• If the low beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction - Daytime Running Lamps.

7. 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.

8. Command the Lamp Test ON and OFF with a scan tool. The lights on indicator and high beam indicator should turn ON and OFF when changing between the commanded states.

• If the lights on indicator and high beam indicator illuminate during the test, replace the BCM.
• If the lights on indicator and high beam indicator do not illuminate during the test or remain illuminated at all times, replace the instrument cluster.

Circuit/System Testing

Warning

The high intensity discharge system produces high voltage and current. To reduce the risk of severe shocks and burns:

* Never open the high intensity discharge system ballast or the arc tube assembly starter.
* Never probe between the high intensity discharge system ballast output connector and the arc tube assembly.

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 3 A 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 3 A 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 3 A 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 3 A 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 (with X88, Z88 and Z75)
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 85 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 30 and ground.

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the appropriate headlamp.
6. Test for less than 5 ohm between the headlamp ground circuit terminal listed below and ground:

* RPO X88 - terminal A
* RPO Z88 - terminal B
* RPO Z75 - terminal 2

• If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the headlamp.
8. Connect a 20 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the headlamp - low beam is activated.

• If the headlamp - low beam does not activate and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the headlamp.
• If the headlamp - low beam does not activate and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the headlamp.

9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
10. 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.

11. If all circuits test normal, test or replace the HDLP LO/HID relay.

Headlamps Malfunction - Daytime Running Lamps (with X88 and Z75)
1. Ignition OFF, disconnect the X4 harness connector at the fuse block - underhood.
2. Connect a test lamp between the control circuit terminal H4 and B+.
3. Command the DRL 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, connect the X4 harness connector at the fuse block - underhood. Disconnect the harness connector at the appropriate daytime running lamp.
5. Test for less than 5 ohm between the daytime running lamp ground circuit terminal listed below and ground:

* RPO X88 - terminal C
* RPO Z75 - terminal B

• 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 A and ground.
7. Command the DRL 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 fuse block - underhood.
• If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the fuse block - underhood.
• If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the daytime running lamp.

8. If all circuits test normal, test or replace the daytime running lamp.

Headlamps Malfunction - High Beam (with X88, Z88 and Z75)
1. Ignition OFF, disconnect the X4 harness connector at the fuse block - underhood.
2. Connect a test lamp between the control circuit terminal C3 and B+.
3. 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, connect the X4 harness connector at the fuse block - underhood. Disconnect the harness connector at the appropriate headlamp.
5. Test for less than 5 ohm between the headlamp ground circuit terminal listed below and ground:

* RPO X88 - terminal A
* RPO Z88 - terminal B
* RPO Z75 - terminal 1

• 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 listed below and ground:

* RPO X88 - terminal B
* RPO Z88 - terminal C
* RPO Z75 - terminal 2

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 fuse block - underhood.
• If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the fuse block - underhood.
• If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the headlamp.

8. If all circuits test normal, test or replace the headlamp.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Headlamp Bulb Replacement (Tahoe, Avalanche) Service and RepairHeadlamp Bulb Replacement (Yukon) Service and RepairHeadlamp Bulb Replacement (Cadillac) Service and Repair
* Headlamp Switch Replacement (Cadillac) Service and RepairHeadlamp Switch Replacement (Except Cadillac) Service and Repair
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)
* Headlamp Replacement (Escalade PLATINUM) Headlamp Replacement (Non HID) Headlamp Replacement (Non HID)Headlamp Replacement (Cadillac Escalade) Headlamp ReplacementHeadlamp Replacement (Tahoe, Avalanche) Headlamp ReplacementHeadlamp Replacement (Chevrolet Tahoe Two-mode Hybrid) Headlamp ReplacementHeadlamp Replacement (Yukon) Headlamp ReplacementHeadlamp Replacement (GMC Yukon Two-mode Hybrid) Headlamp Replacement
* Headlamp Ballast Replacement Headlamp Ballast Replacement
* Underhood Electrical Center or Junction Block Replacement Underhood Electrical Center or Junction Block Replacement
* Turn Signal Multifunction Switch Replacement Turn Signal Multifunction Switch Replacement
* Control Module References Control Module References for BCM or instrument panel replacement, setup, and programming

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