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Daytime Running Lamps Malfunction (With T4Q)




Daytime Running Lamps Malfunction (With T4Q)

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

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 body control module (BCM) provides a 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 resistor via the DRL resistor control circuit. When the BCM applies ground to the DRL resistor control circuit, the DRL signal circuits to the right and left headlamp assemblies are pulled low. The DRL signal circuits are direct inputs to the right and left headlamp control modules. When the DRL signal circuits are provided with ground, the right and left headlamp control modules respond by turning OFF the low beam headlamps and activating the DRLs. Any function or condition that turns the headlamps ON 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
1. Ignition OFF, disconnect the harness connector at the DRL resistor.
2. Connect a test lamp between the control circuit terminal C 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 harness connector at the DRL resistor.
5. Disconnect the harness connector at the appropriate headlamp assembly.
6. Connect a test lamp between the signal circuit terminal D and B+.
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 signal circuit for a short to ground. If the circuit tests normal, replace the DRL resistor.
• If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the DRL resistor.

8. Connect a test lamp between the signal circuit terminal B and B+.
9. 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 signal circuit for a short to ground. If the circuit tests normal, replace the DRL resistor.
• If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the DRL resistor.

10. If all circuits test normal, replace the headlamp assembly.

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.

* Ambient Light Sensor Replacement (Service and Repair)
* Headlamp Replacement (Cadillac Escalade) (Headlamp Replacement (Cadillac Escalade))Headlamp Replacement (GMC Yukon Two-mode Hybrid) (Headlamp Replacement (GMC Yukon Two-mode Hybrid))Headlamp Replacement (Yukon) (Headlamp Replacement (Yukon))Headlamp Replacement (Chevrolet Tahoe Two-mode Hybrid) (Headlamp Replacement (Chevrolet Tahoe Two-mode Hybrid))Headlamp Replacement (Tahoe, Avalanche) (Headlamp Replacement (Tahoe, Avalanche))Headlamp Replacement (Escalade PLATINUM) (Headlamp Replacement (Escalade Platinum))Headlamp Replacement (Non HID) (Headlamp Replacement (Non HID))
* Headlamp Control Module Replacement (Escalade PLATINUM) (Headlamp Control Module Replacement (Escalade Platinum))
* Control Module References (Programming and Relearning) for BCM or headlamp control module replacement, setup, and programming

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