Brake Lamp

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/System Description

When the headlamp switch is placed in the HEAD or PARK position, ground is applied to the park lamp switch ON signal circuit to the body control module (BCM). The BCM responds by applying voltage to the park lamps, tail lamps, and license lamps control circuits illuminating the park, tail, and license lamps.

Reference Information

Schematic Reference

Exterior Lights 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 scan tool information

Circuit/System Verification

1. Ignition ON.
2. Verify the scan tool Parking Lamp Switch parameter changes between Active and Inactive while commanding the park lamps ON and OFF with the headlamp switch.


• If the parameter does not change
  Refer to Park Lamp Switch Malfunction.



• If the parameter changes


3. Verify the left park lamps turn ON and OFF when commanding the Left Park Lamps ON and OFF with a scan tool.


• If the left park lamps do not turn ON and OFF
  Refer to Park Lamps Malfunction.



• If the left park lamps turn ON and OFF


4. Verify the right park lamps turn ON and OFF when commanding the Right Park Lamps ON and OFF with a scan tool.


• If the right park lamps do not turn ON and OFF
  Refer to Park Lamps Malfunction.



• If the right park lamps turn ON and OFF


5. Verify the license plate lamps turn ON and OFF when commanding the License Plate Lamps ON and OFF with a scan tool.


• If the license plate lamps do not turn ON and OFF
  Refer to License Plate Lamps Malfunction.



• If the license plate lamps turn ON and OFF


6. All OK.

Circuit/System Testing

Park Lamp Switch Malfunction

1. Ignition OFF, all doors closed, all accessories OFF, disconnect the harness connector at the S30 headlamp switch. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 15 Ω between the ground circuit terminal 6 and ground.


• If 15 Ω or greater


1. Ignition OFF.
2. 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 15 Ω


3. Ignition ON.
4. Verify the scan tool Park Lamps Switch parameter is Inactive.


• If not Inactive


1. Ignition OFF, disconnect the X1 harness connector at the K9 body control module.
2. Test for infinite resistance between the signal circuit terminal 3 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 Inactive


5. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the ground circuit terminal 6.
6. Verify the scan tool Park Lamps Switch parameter is Active.


• If not Active


1. Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON.
2. Test for less than 1 V between the signal circuit terminal 3 and ground.


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



• If less than 1 V


3. 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 Active


7. Test or replace the S30 headlamp switch.

Park Lamps Malfunction

1. Ignition OFF, exterior lamps OFF, trunk latch latched, disconnect the harness connector at the appropriate park lamp.
2. Test for less than 5 Ω between the appropriate ground circuit terminal and ground.


• If 5 Ω or greater


1. Ignition OFF.
2. 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


3. Connect a test lamp between the appropriate control circuit terminal and ground, ignition ON.
4. Verify the test lamp turns ON and OFF when commanding the appropriate Park Lamps ON and OFF with a scan tool.


• If the test lamp is always OFF


1. Ignition OFF, disconnect the appropriate harness connector listed below at the K9 body control module.
• X4
• X5
2. 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


3. 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


1. Ignition OFF, disconnect the appropriate harness connector listed below at the K9 body control module.
• X4
• X5
2. 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, replace the K9 body control module.




• If the test lamp turns ON and OFF


5. Test or replace the appropriate park lamp.

License Plate Lamps Malfunction

1. Ignition OFF, exterior lamps OFF, trunk latch latched, remove both E7 license plate lamp bulbs.
2. Test for less than 5 Ω between each ground circuit terminal 2 and ground.


• If 5 Ω or greater


1. Ignition OFF.
2. 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


3. Connect a test lamp between the E7L license plate lamp – left control circuit terminal 1 and ground, ignition ON.
4. Verify the test lamp turns ON and OFF when commanding the License Plate Lamps ON and OFF with a scan tool.


• If the test lamp is always OFF


1. Ignition OFF, disconnect the X4 harness connector at the K9 body control module.
2. 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


3. 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


1. Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON.
2. 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, replace the K9 body control module.




• If the test lamp turns ON and OFF


5. Ignition OFF.
6. Connect a test lamp between the E7R license plate lamp – right control circuit terminal 1 and ground, ignition ON.
7. Verify the test lamp turns ON and OFF when commanding the License Plate Lamps ON and OFF with a scan tool.


• If the test lamp is always OFF


1. Ignition OFF, disconnect the X4 harness connector at the K9 body control module.
2. 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


3. 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 the test lamp turns ON and OFF


8. Test or replace the appropriate E7 license plate lamp bulb.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Rear License Plate Lamp Replacement
• Parking and Turn Signal Lamp Bulb Replacement
• Tail Lamp Bulb Replacement
• Front Side Marker Lamp Replacement
• Rear Side Marker Lamp Replacement
• Headlamp, Instrument Panel Lamp Dimmer, and Fog Lamp Switch Replacement
• Tail Lamp Replacement - Inboard
• Tail Lamp Replacement - Outboard
• Control Module References for BCM replacement, programming, and setup