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 |
|---|---|---|---|---|
Daytime Running Lamp Relay B+ | 1 | 1 | -- | -- |
Headlamp LO/HID Relay B+ | 1 | 1 | -- | -- |
High Beam Relay B+ | 1 | 1 | -- | -- |
Ambient Light Sensor Signal Circuit | B2645 03 | B2645 07 | B2645 07 | -- |
Headlamp Flash to Pass Signal | 4 | 4 | 4 | -- |
Headlamp Dimmer Switch Signal | 4 | 4 | 4 | -- |
Daytime Running Lamp Relay Control | 3 | 3 | B2600 00 | -- |
Headlamp Low Beam Control | 1 | 1 | 1 | -- |
Headlamp Low Beam Relay Control | 1 | 1 | B2575 00 | -- |
Headlamp Switch Off Control | B257A 00 | 2 | 2 | -- |
Headlamp Switch On Control | B257A 00 | 1 | 1 | -- |
Headlamp High Beam Control | 1 | 1 | 1 | -- |
Headlamp High Beam Relay Control | 1 | 1 | B2580 00 | -- |
Park Lamp Switch On Control | B257A 00 | B257A 00 | 2 | -- |
Ambient Light Sensor Ground Circuit | -- | B2645 07 | -- | -- |
Headlamp Switch Ground | -- | 2 | -- | -- |
Turn Signal/Multifunction Switch Malfunction | -- | 4 | -- | -- |
| ||||
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
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References 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 |
Circuit/System Testing
Daytime Running Lamps Malfunction -- Z75/X88
- Ignition OFF, disconnect the harness connector X4 at the underhood fuse block.
- Connect a test lamp between the daytime running lamps relay control circuit terminal H4 and B+.
- Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.
- Ignition OFF, reconnect the harness connector X4 at the underhood fuse block.
- Disconnect the harness connector at the appropriate daytime running lamp.
- Test for less then 5 ohms between the gound circuit listed below and ground.
- Ignition OFF, connect a test lamp between the control circuit terminal A and ground.
- Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF.
- If all circuits test normal, replace the inoperative daytime running lamp.
| ⇒ | 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. |
| • | 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. |
| ⇒ | If the test lamp is always ON, test the contol 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. |
Daytime Running Lamps Malfunction -- Z88
- Ignition OFF, disconnect the harness connector X4 at the underhood fuse block.
- Connect a test lamp between the daytime running lamps relay control circuit terminal H4 and B+.
- Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.
- Ignition OFF, reconnect the harness connector X4 at the underhood fuse block.
- Disconnect the harness connector at the appropriate headlamp.
- Test for less then 5 ohms between the gound circuit terminal B and ground.
- Ignition OFF, connect a test lamp between the control circuit terminal A and ground.
- Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF.
- If all circuits test normal, replace the inoperative headlamp.
| ⇒ | 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. |
| ⇒ | If more than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If the test lamp is always ON, test the contol 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, programming, and setup |
