Document ID: 2216226

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 provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Headlamp Switch B+	B1405 03, B1529 03, B257B 03	B257B 03	—	—
Headlamp Switch Signal	B257B 03	B257B 03	B257B 07	—
Front Fog Lamp Relay Control	B2530 02	B2530 04	B2530 01	—
Front Fog Lamp Control	1	1	1	—
Front Fog Lamp Ground – Left	—	1	—	—
Front Fog Lamp Ground – Right	—	1	—	—
1. Front Fog Lamps Malfunction

Circuit/System Description

The front fog lamp relay is supplied with battery voltage at all times. The front fog lamp switch signal circuit is grounded through a resistor momentarily when the front fog lamp switch is pressed. The body control module (BCM) energizes the front fog lamp relay by applying ground to the front fog lamp relay control circuit. When the front fog lamp relay is energized, the relay contacts close and battery voltage is applied through the front fog lamp fuse to the front fog lamp control circuit which illuminates the front fog lamps.

Reference Information

Schematic Reference

Fog Lights 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 Verification

Ignition ON, headlamps ON.
Verify the scan tool Front Fog Lamps Switch parameter changes between Active and Inactive while commanding the front fog lamps ON and OFF with the front fog lamp switch.

If the parameter does not change
Refer to Front Fog Lamp Switch Malfunction.

If the parameter changes

Verify the front fog lamps turn ON and OFF when commanding the Front Fog Lamps ON and OFF with a scan tool.

If the front fog lamps do not turn ON and OFF
Refer to Front Fog Lamps Malfunction.

If the front fog lamps turn ON and OFF

Verify the front fog lamp indicator on the instrument cluster turns ON and OFF while commanding the front fog lamps ON and OFF with the front fog lamp switch.

If the front fog lamp indicator does not turn ON and OFF
Refer to Front Fog Lamp Indicator Malfunction.

If the front fog lamp indicator turns ON and OFF

All OK.

Circuit/System Testing

Front Fog Lamp Switch Malfunction

Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the S30 headlamp switch, ignition ON.
Test for B+ between the B+ circuit terminal 1 and ground.

If less than B+

Ignition OFF, disconnect the X3 harness connector at the K9 body control module.
Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, replace the K9 body control module.

If B+

Verify the scan tool LED Backlight Dimming Command parameter is greater than 40%.

If 40% or less

Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON.
Test for less than 1 V between the signal circuit terminal 12 and ground.

If 1 V or greater, repair the short to voltage on the circuit.
If less than 1 V, replace the K9 body control module.

If greater than 40%

Install a 3 A fused jumper wire between the signal circuit terminal 12 and the B+ circuit terminal 1.
Verify the scan tool LED Backlight Dimming Command parameter is less than 30%.

If 30% or greater

Ignition OFF, disconnect the X1 harness connector at the K9 body control module.
Test for infinite resistance between the signal circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

Test for less than 2 Ω in the signal circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, replace the K9 body control module.

If less than 30%

Test or replace the S30 headlamp switch.

Front Fog Lamps Malfunction

Ignition OFF, disconnect the X2 harness connector at the X50A fuse block – underhood.
Connect a test lamp between the control circuit terminal 19 and B+, ignition ON.
Verify the test lamp turns ON and OFF when commanding the Front Fog Lamps ON and OFF with a scan tool.

If the test lamp is always OFF

Ignition OFF, disconnect the appropriate harness connector listed below at the K9 body control module, ignition ON.

X3 – without T3U
X5 – with T3U

Test for less than 1 V between the control circuit terminal and ground.

If 1 V or greater, repair the short to voltage on the circuit.

If less than 1 V

Ignition OFF.
Test for less than 2 Ω in the control circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, replace the K9 body control module.

If the test lamp is always ON

Ignition OFF, disconnect the appropriate harness connector listed below at the K9 body control module, ignition ON.

X3 – without T3U
X5 – with T3U

Test for infinite resistance between the control circuit terminal and ground.

If less than infinite resistance, repair the short to ground on the circuit.
If infinite resistance, replace the K9 body control module.

If the test lamp turns ON and OFF

Ignition OFF, connect the X2 harness connector at the X50A fuse block – underhood.
Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E29 fog lamp.
Test for less than 5 Ω between the ground circuit terminal A and ground.

If 5 Ω or greater

Ignition OFF.
Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 5 Ω

Connect a test lamp between the control circuit terminal B and ground, ignition ON.
Verify the test lamp turns ON and OFF when commanding the Front Fog Lamps ON and OFF with a scan tool.

If the test lamp is always OFF

Ignition OFF, disconnect the X1 harness connector at the X50A fuse block – underhood.
Test for infinite resistance between the control circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

Test for less than 2 Ω in the control circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, replace the X50A fuse block – underhood.

If the test lamp is always ON

Ignition OFF, disconnect the X1 harness connector at the X50A fuse block – underhood, ignition ON.
Test for less than 1 V between the control circuit and ground.

If 1 V or greater, repair the short to voltage on the circuit.
If less than 1 V, replace the X50A fuse block – underhood.

If the test lamp turns ON and OFF

Test or replace the appropriate E29 fog lamp.

Front Fog Lamp Indicator Malfunction

Ignition ON.
Verify the front fog lamp indicator turns ON and OFF when commanding the Instrument Cluster All Indicators Test ON and OFF with a scan tool.

If the front fog lamp indicator is always OFF or remains ON
Replace the P16 instrument cluster.

If the front fog lamp indicator turns ON and OFF

Replace the K9 body control module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Front Fog Lamp Replacement
Accessory Wiring Junction Block Replacement
Headlamp, Instrument Panel Lamp Dimmer, and Fog Lamp Switch Replacement
Control Module References for BCM and instrument cluster replacement, programming, and setup

Document ID: 2715278