Document ID: 2636792

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic approach.
Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Ambient Light Sensor Signal	B2645 03	B2645 07	B2645 07	—
Daytime Running Lamp Control - Left (T4F)	B2600 02	B2600 04	B2600 01	—
Daytime Running Lamp Control - Right (T4F)	B2605 02	B2605 04	B2605 01	—
Daytime Running Lamp Control (T4A)	1	1	1	—
Ambient Light Sensor Ground	—	B2645 07	1	—
Daytime Running Lamp Ground - Left (T4F)	—	1	—	—
Daytime Running Lamp Ground - Right (T4F)	—	1	—	—
Daytime Running Lamp Ground (T4A)	—	1	—	—
1. Daytime Running Lamps Malfunction

Circuit/System Description

Daytime Running Lamps (T4A)

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 body control module (BCM) provides a 5 V reference signal to the ambient light sensor which is permanently grounded. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic headlamp system control when the headlamp switch is in the AUTO position. In daylight conditions the BCM will command the DRL’s ON by applying voltage to the DRL control circuit illuminating the DRL’s. Any function or condition that turns on the headlamps will cancel DRL operation.

Daytime Running Lamps (T4F)

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 body control module (BCM) provides a 5 V reference signal to the ambient light sensor which is permanently grounded. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic headlamp system control when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying a pulse width modulated (PWM) voltage to the left and right DRL control circuits illuminating the DRLs. Any function or condition that turns on the headlamps will cancel DRL operation.

Reference Information

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

Daytime Running Lamp Malfunction – with T4F

Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E4 daytime running lamp.
Test for less than 5 Ω between the ground circuit terminal 2 and ground.

If 5 Ω or greater

Ignition OFF.
Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 5 Ω

Connect a test lamp between the control circuit terminal 1 and ground, ignition ON.
Verify the test lamp turns ON and OFF when commanding the Dedicated Daytime Running Lamp Command ON and OFF with a scan tool.

If the test lamp is always OFF

Ignition OFF, disconnect the X4 harness connector at the K9 body control module.
Test for infinite resistance between the control circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

Test for less than 2 Ω in the control circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, replace the K9 body control module.

If the test lamp is always ON

Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON.
Test for less than 1 V between the control circuit terminal and ground.

If 1 V or greater, repair the short to voltage on the circuit.
If less than 1 V, replace the K9 body control module.

If the test lamp turns ON and OFF

Test or replace the appropriate E4 daytime running lamp.

Daytime Running Lamp Malfunction – with T4A

Ignition OFF, disconnect the X2 harness connector at the X50A fuse block – underhood.
Connect a test lamp between the control circuit terminal 19 and B+, ignition ON.
Verify the test lamp turns ON and OFF when commanding the Front Fog Lamps ON and OFF with a scan tool.

If the test lamp is always OFF

Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON.
Test for less than 1 V between the control circuit terminal and ground.

If 1 V or greater, repair the short to voltage on the circuit.

If less than 1 V

Ignition OFF.
Test for less than 2 Ω in the control circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, replace the K9 body control module.

If the test lamp is always ON

Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON.
Test for infinite resistance between the control circuit terminal and ground.

If less than infinite resistance, repair the short to ground on the circuit.
If infinite resistance, replace the K9 body control module.

If the test lamp turns ON and OFF

Ignition OFF, connect the X2 harness connector at the X50A fuse block – underhood.
Ignition OFF, exterior lamps OFF, disconnect the harness connector at the E4C daytime running lamp – left.
Test for less than 5 Ω between the ground circuit terminal 2 and ground.

If 5 Ω or greater

Ignition OFF.
Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 5 Ω

Connect a test lamp between the control circuit terminal 1 and ground, ignition ON.
Verify the test lamp turns ON and OFF when commanding the Front Fog Lamps ON and OFF with a scan tool.

If the test lamp is always OFF

Ignition OFF, disconnect the X1 harness connector at the X50A fuse block – underhood.
Test for infinite resistance between the control circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

Test for less than 2 Ω in the control circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, replace the X50A fuse block – underhood.

If the test lamp is always ON

Ignition OFF, disconnect the X1 harness connector at the X50A fuse block – underhood, ignition ON.
Test for less than 1 V between the control circuit and ground.

If 1 V or greater, repair the short to voltage on the circuit.
If less than 1 V, replace the X50A fuse block – underhood.

If the test lamp turns ON and OFF

Test or replace the appropriate E4 daytime running lamp.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Daytime Running Lamp Replacement
Daytime Running Lamp Bulb Replacement
Control Module References for BCM replacement, programming, and setup

Operation	Task	Skill	Hours
Remove & Replace	Bulbs · Exterior Bulbs, R&R · Daytime Lamp · With Zl1 · Left Side	C	0.9
Remove & Replace	Bulbs · Exterior Bulbs, R&R · Daytime Lamp · With Zl1 · Right Side	C	0.9
Remove & Replace	Bulbs · Exterior Bulbs, R&R · Daytime Lamp · Without Zl1 · Left Side	C	0.5
Remove & Replace	Bulbs · Exterior Bulbs, R&R · Daytime Lamp · Without Zl1 · Right Side	C	0.3