Daytime Running Lamps Malfunction (With Z88, Z75, and Z88)
Daytime Running Lamps Malfunction (With Z88, Z75, and Z88)
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
Daytime Running Lamps without HID
The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 volts depending on outside lighting conditions. The HVAC control module provides a low reference ground and 5-volt reference signal to the ambient light sensor. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the low beam headlamps ON. Any function or condition that turns on the headlamps will cancel DRL operation.
Daytime Running Lamps with HID
The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 volts depending on outside lighting conditions. The HVAC control module provides a low reference ground and 5-volt reference signal to the ambient light sensor. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL relay control circuits. When the BCM applies ground to the relay control circuit, the DRL relay coil energizes causing the switch contacts to close. With the DRL relay switch contacts closed, battery voltage flows through the DRL fuse to the left and right DRL lamps. Any function or condition that turns on the headlamps will cancel DRL operation.
Diagnostic Aids
Important: This diagnostic procedure assumes that the low beam headlamps are operating within specifications. If the low beam headlamps are inoperative, diagnose the low beam headlamp malfunction before proceeding with the following diagnostic.
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) 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
Ignition ON, verify with a scan tool the park brake switch parameter displays Released.
If not as specified, refer to Park Brake System Diagnosis (Park Brake System Diagnosis)
Circuit/System Testing
Daytime Running Lamps Malfunction - with Z75/X88
1. Ignition OFF, disconnect the harness connector X4 at the underhood fuse block.
2. Connect a test lamp between the daytime running lamps relay control circuit terminal H4 and B+.
3. Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF 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, reconnect the harness connector X4 at the underhood fuse block.
5. Disconnect the harness connector at the appropriate daytime running lamp.
6. Test for less then 5 ohms between the ground circuit listed below and ground.
* ground circuit terminal B -Z75
* ground circuit terminal C -X88
• If less than the specified range, test the ground circuit for an open/high resistance.
7. Ignition OFF, connect a test lamp between the control circuit terminal A and ground.
8. Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF.
• If the test lamp is always ON, test the control circuit for a short to voltage. If the control 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, and the DRL fuse is not open, replace the underhood fuse block.
9. If all circuits test normal, replace the inoperative daytime running lamp.
Daytime Running Lamps Malfunction - with Z88
1. Ignition OFF, disconnect the harness connector X4 at the underhood fuse block.
2. Connect a test lamp between the daytime running lamps relay control circuit terminal H4 and B+.
3. Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF 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, reconnect the harness connector X4 at the underhood fuse block.
5. Disconnect the harness connector at the appropriate headlamp.
6. Test for less then 5 ohms between the ground circuit terminal B and ground.
• If more than the specified range, test the ground circuit for an open/high resistance.
7. Ignition OFF, connect a test lamp between the control circuit terminal A and ground.
8. Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF.
• If the test lamp is always ON, test the control circuit for a short to voltage. If the control 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, and the DRL fuses are not open, replace the underhood fuse block.
9. If all circuits test normal, replace the inoperative headlamp.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Headlamp Replacement (Non HID) (Service and Repair)Headlamp Replacement (Cadillac Escalade) (Service and Repair)Headlamp Replacement (Escalade PLATINUM) (Service and Repair)Headlamp Replacement (Tahoe, Avalanche) (Service and Repair)Headlamp Replacement (Chrevrolet Tahoe Two-mode Hybrid) (Service and Repair)Headlamp Replacement (Yukon) (Service and Repair)Headlamp Replacement (GMC Yukon Two-mode Hybrid) (Service and Repair)
* Headlamp Bulb Replacement (Cadillac) (Service and Repair)Headlamp Bulb Replacement (Yukon) (Service and Repair)Headlamp Bulb Replacement (Tahoe, Avalanche) (Service and Repair)
* Ambient Light Sensor Replacement (Service and Repair)
* Daytime Running Lamp Bulb Replacement (GMC) (Service and Repair)Daytime Running Lamp Bulb Replacement (Cadillac) (Service and Repair)
* Control Module References (Programming and Relearning) for BCM or headlamp control module replacement, setup, and programming