• | 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. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Headlamp Switch Off Signal | B257A 00 | 2 | 2* | -- |
Park Lamp Switch On Signal | B257A 00 | B257A 00 | B257A 00* | -- |
Headlamp Switch On Signal | B257A 00 | 2 | 2* | -- |
Headlamp Ground | -- | 1 | -- | -- |
* Internal damage to the headlamp switch may occur if shorted to B+ 1. Headlamps Malfunction - Low Beam 2. Headlamp Switch Malfunction |
The body control module (BCM) supplies a B+ reference voltage through each of the headlamp switch signal circuits to the headlamp switch. When the headlamp switch is in the AUTO position, all headlamp switch signal circuits to the BCM are open and the BCM operates in the automatic mode. When the headlamp switch is turned to the PARK position, only the park lamp switch signal circuit is pulled low signaling the park lamps ON request. When the headlamp switch is turned to the HEAD position, the park lamp and headlamp switch signal circuits are both pulled low, signaling the headlamps ON request. When the headlamp switch is turned to the OFF position, only the headlamp off switch signal circuit is pulled low, signaling the lights OFF request.
Ignition ON.
The BCM receives a mismatch signal between the headlamps OFF signal circuit, the headlamps ON signal circuit and the park lamps ON signal circuit.
The BCM disregards the headlamp switch input and defaults to automatic headlamp function.
• | The condition responsible for setting the DTC no longer exists. |
• | A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred. |
Headlights/Daytime Running Lights (DRL) Schematics
Exterior Lighting Systems Description and Operation
Control Module References for scan tool information
Ignition ON with the headlamp switch in the Auto position, observe the scan tool Exterior Lighting parameters listed below. All parameters should be Inactive.
• | Auto Hdlp. Disable Sw. |
• | Headlamp Switch |
• | Parklamp Switch |
• | Headlamp switch ON signal terminal 1 |
• | Park lamp switch ON signal terminal 2 |
• | Headlamp switch OFF signal terminal 3 |
⇒ | If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
Important: If the switch tests open in any switch position other than Auto, test the switch signal circuits for a short to voltage before replacing the switch.
⇒ | If not the specified value, replace the headlamp switch. |
⇒ | If not the specified value, replace the headlamp switch. |
⇒ | If not the specified value, replace the headlamp switch. |
⇒ | If not the specified value, replace the headlamp switch. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for BCM replacement, setup, and programming |