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 has overviews of all diagnostic categories.

DTC Descriptors

DTC B257C 00

Left Headlamp Assembly Malfunction

DTC B257D 00

Right Headlamp Assembly Malfunction

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Left Headlamp Assembly Voltage Supply	B257C 00	B257C 00	B257C 00	-
Right Headlamp Assembly Voltage Supply	B257D 00	B257D 00	B257D 00	-

Circuit/System Description

When the headlight switch is placed in low beam position, the body control module (BCM) energizes the low beam headlamp relay which passes battery voltage to the respective headlamp voltage supply circuits. Each headlamp monitors this voltage and passes this information to the headlamp control module via the local interconnect network (LIN) communication bus.

Conditions for Running the DTC

The headlamps are ON.

Conditions for Setting the DTC

The headlamp control module detects a difference between the reported state of the headlamp from the headlamp and the reported state from the BCM.

Action Taken When the DTC Sets

The appropriate headlamp is inoperative.

Conditions for Clearing the DTC

The condition responsible for setting the DTC no longer exists.

Diagnostic Aids

If both DTCs B257C and B257D are set, test the low beam relay for an open condition.

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

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

Control Module References for information on diagnostic tools

Circuit/System Verification

Ignition ON, command the headlamps ON and OFF with the headlamp switch.

Circuit/System Testing

1.	Ignition OFF, disconnect the appropriate harness connector at the inoperative headlamps listed below:

•

E13L Headlamp Assembly - Left

•

E13R Headlamp Assembly - Right

2.	Test for less than 5 Ω between the appropriate headlamp ground circuit harness connector terminal 1 and ground.

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

4.	Reconnect the headlamp connector and remove the appropriate fuse listed below:

•

F50 UA Left Low Beam

•

F49 UA Right Low Beam

5.	Verify that the appropriate headlamp does not illuminate.

6.	If the headlamp does illuminate, test the fuse output circuit for a short to voltage.

7.	Install a 10 A fused jumper wire between appropriate fuse output contact and B+. Verify that the appropriate low beam illuminates.

8.	If the headlamp does not illuminate, test the fuse output circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the appropriate bulb.

9.	If all circuits test normal, replace the K26 Headlamp Control Module.

Component Testing

Relay Test

1.	Ignition OFF, disconnect the KR49 Headlamp Low Beam Relay.

2.	Test for 60-180 Ω between terminals 1 and 2.

3.	If the resistance is not within the specified range, replace the KR49 Headlamp Low Beam Relay.

4.	Test for infinite resistance between the following terminals:

•

1 and 3

•

3 and 5

•

2 and 5

•

1 and 3

5.	If not the specified value, replace the KR49 Headlamp Low Beam Relay.

6.	Install a 15 A fused jumper wire between relay terminal 1 and 12 V. Install a jumper wire between relay terminal 2 and ground. Test for less than 2 Ωbetween terminals 3 and 5.

7.	If greater than the specified range, replace the KR49 Headlamp Low Beam Relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

•	Relay Replacement (Attached to Wire Harness)

•	Relay Replacement (Attached to Wire Harness)

•	Headlamp Replacement

•	Control Module References for headlamp control module replacement, setup, and programming