Diagnostic Instructions

DTC Descriptors

DTC B2580 02: Left High Beam Circuit Low Voltage

DTC B2580 05: Left High Beam Circuit Open or High Voltage

DTC B3866 02: Right High Beam Circuit Low Voltage

DTC B3866 05: Right High Beam Circuit Open or High Voltage

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
LF High Beam Headlamp Control	B2580 00	B2580 05	B2580 05	--
RF High Beam Headlamp Control	B3866 00	B3866 05	B3866 05	--
LF High Beam Headlamp Ground	--	1	--	--
RF High Beam Headlamp Ground	--	1	--	--
1. Headlamps Malfunction

Circuit/System Description

The headlamp switch is supplied with voltage from the instrument panel cluster (IPC) by two signal circuits, the headlamps signal circuit and the park lamp signal circuit. When the headlamp switch is placed in either the AUTO or HEAD position, the headlamps signal circuit is provided with ground through the switch contacts of the headlamp switch to a common headlamp switch ground back to the IPC. The IPC interprets the flow of voltage and responds by sending a serial data message to the underhood electrical center (UEC) requesting the headlamps be activated. When the headlamp high beam switch is activated, the IPC sends a serial data message to the UEC requesting the high beams be activated. The UEC responds by applying voltage to the left and right high beam headlamp control circuits illuminating the high beam headlamps. Ground for the left headlamp is supplied at G101 and the right headlamp receives ground at G102.

Conditions for Running the DTC

Conditions for Setting the DTC

B2580 00

The DTC will set when the UEC detects a short to ground in the left high beam headlamp control circuit when the high beam headlamps are being commanded ON.

B2580 05

The DTC will set when the UEC detects a short to voltage or an open/high resistance in the left high beam headlamp control circuit when the high beam headlamps are being commanded ON.

B3866 00

The DTC will set when the UEC detects a short to ground in the right high beam headlamp control circuit when the high beam headlamps are being commanded ON.

B3866 05

The DTC will set when the UEC detects a short to voltage or an open/high resistance in the right high beam headlamp control circuit when the high beam headlamps are being commanded ON.

Actions Taken When the DTC Sets

The UEC will disable the headlamp high beam control circuit that has a fault present.

Conditions for Clearing the DTC

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

1. Ignition OFF, disconnect the harness connector at the inoperative headlamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal 9 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the control circuit terminal 2 and ground.
4. Command the Front High Beam Test ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the UEC.

⇒	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, replace the UEC.

5. If all circuits test normal, replace the inoperative high beam headlamp.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.