GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2002 🢒 Grand Am 🢒 Body and Accessories 🢒 Instrument Panel, Gages, and Console 🢒 DTC B2578

Circuit Description

The body control module (BCM) turns on the automatic lighting control (ALC) relay when the ambient light sensor senses a dark condition. Battery positive voltage is supplied to the ALC relay at all times through the LH HDLP fuse. The BCM grounds the ALC relay control circuit in order to activate the relay.

Conditions for Running the DTC
    • The ignition switch is in the ON position.
    • The ambient light sensor senses a dark condition (ALC headlamps on).

Conditions for Setting the DTC

The ALC relay control circuit is shorted to voltage for 1 second.

Action Taken When the DTC Sets
    • The BCM turns off the ALC relay control for the remainder of the ignition cycle.
    • The SERVICE indicator illuminates.
    • The check gauges chime sounds.

Conditions for Clearing the DTC
    • The conditions for setting the DTC are no longer present.
    • A history DTC clears after 100 malfunction free ignition cycles.
    • The BCM receives the clear code command from the scan tool.

Diagnostic Aids

If the DTC is a history DTC, the problem may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

The numbers below refers to the step numbers on the diagnostic table.

  1. Listen for an audible click when the ALC relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

Step

Action

Yes

No

Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics

1

Did you perform the Lighting System Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the ALC relay ON and OFF.

Does the ALC relay turn ON and OFF with each command?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Test for a short to voltage in the control circuit of the ALC relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 6

Go to Step 4

4

Inspect for poor connections at the harness connector of the body control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 6

Go to Step 5

5

Important: Perform the set up procedure for the body control module.

Replace the body control module. Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 6

--

6
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK