B2577

DTC B2577

CIRCUIT DESCRIPTION
The body control module (BCM) energizes the headlamp relay when the ambient light sensor senses a dark condition. Battery positive voltage is supplied to the headlamp relay when the ignition is in the RUN position. The BCM grounds the headlamp relay control circuit in order to activate the relay.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC B2577 Headlamp Control Circuit Low.

CONDITIONS FOR RUNNING THE DTC
- The ignition switch is in the RUN position.
- The ambient light sensor senses a light condition, automatic lamp control (ALC) headlamps OFF.

CONDITIONS FOR SETTING THE DTC
Either of the following conditions will set this DTC:
- The headlamp relay control circuit is open for 5 seconds.
- The headlamp relay control circuit is shorted to ground for 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
The headlamps will remain illuminated or will not illuminate in ALC mode.

CONDITIONS FOR CLEARING THE DTC
- The BCM receives the clear code command from the scan tool.
- A current DTC will clear when the conditions for setting the DTC are no longer present.
- A history DTC clears after 100 malfunction free ignition cycles.

DIAGNOSTIC AIDS
- If the headlamp relay control circuit is open, the ALC headlamps will be inoperative.
- In the headlamp relay control circuit is shorted to ground, the ALC headlamps will be always on.
- If the DTC is a history DTC, the problem may be intermittent.

TEST DESCRIPTION

Step 1 - Step 13:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the headlamp relay operates. Command both the ON and OFF states. Repeat the commands, as necessary.
3. Tests for voltage at the coil side of the headlamp relay. The ignition switch supplies battery positive voltage to the coil side of the headlamp relay.
4. Verifies that the BCM is providing ground to the headlamp relay.
5. Tests if ground is constantly being applied to the headlamp relay.