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 (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
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 V depending on outside lighting conditions. The HVAC control module provides a low reference ground and 5 V 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 V depending on outside lighting conditions. The HVAC control module provides a low reference ground and 5 V 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
Note: 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 (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 (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Ignition ON, Headlamps OFF, command the Low Beams ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when changing between the commanded states.
• If the low beam headlamps do not change between the commanded states, refer to Headlamps Malfunction (With X88, Z75, and Z88) (Headlamps Malfunction (With X88, Z75, and Z88))Headlamps Malfunction (With T4Q) (Headlamps Malfunction (With T4Q)).
2. Headlamps OFF, command the DRL ON and OFF with a scan tool. The daytime running lights should turn ON and OFF when changing between the commanded states.
• If the daytime running lights do not change between the commanded states, refer to Daytime Running Lamp Malfunction.
3. Observe the scan tool Ambient Light Status parameter while supplying sufficient light to simulate daylight conditions to the ambient light sensor. After 30 seconds, the parameter should be Day.
• If not the specified value, refer to Ambient Light Sensor Malfunction.
Circuit/System Testing
Daytime Running Lamp 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 ohm between the ground circuit listed below and ground.
* Terminal B (Z75)
* 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 daytime running lamp.
Daytime Running Lamp 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 ohm 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 headlamp.
Ambient Light Sensor Malfunction
1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
2. Ignition OFF, test for less than 5 ohm between the ground circuit terminal listed below and ground.
* Terminal C (with CJ2)
* Terminal B (without CJ2)
• If greater than the specific range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 4.65 V.
• If less than the specified range, test the signal circuit terminal for a short to ground. If the circuit tests normal, replace the BCM.
4. Install a 3 A fused jumper wire between the signal circuit terminal listed below and the ground circuit terminal. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 V.
* Terminal D (with CJ2)
* Terminal A (without CJ2)
• If greater than the specified range, test the signal circuit for a short to voltage an open/high resistance. If the circuit tests normal, replace the BCM.
5. If all circuits test normal, replace the ambient light sensor.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
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* Headlamp Bulb Replacement (Cadillac) (Headlamp Bulb Replacement (Cadillac))Headlamp Bulb Replacement (Tahoe, Avalanche) (Headlamp Bulb Replacement (Tahoe, Avalanche))Headlamp Bulb Replacement (Yukon) (Headlamp Bulb Replacement (Yukon))
* Ambient Light Sensor Replacement (Service and Repair)
* Daytime Running Lamp Bulb Replacement (GMC) (Daytime Running Lamp Bulb Replacement (GMC))Daytime Running Lamp Bulb Replacement (Cadillac) (Daytime Running Lamp Bulb Replacement (Cadillac))
* Underhood Electrical Center or Junction Block Replacement (Underhood Electrical Center or Junction Block Replacement)
* Control Module References (Programming and Relearning) for BCM or headlamp control module replacement, setup, and programming