锟斤拷 If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the fog lamp front.
8. Connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the fog lamp front is
activated.
锟斤拷 If the fog lamp front does not activate and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests
normal, test or replace the fog lamp front.
锟斤拷 If the fog lamp front does not activate and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal,
test or replace the fog lamp front.
9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
10. Command the Fog Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded
states.
锟斤拷 If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
锟斤拷 If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace
the BCM.
11. If all circuits test normal, test or replace the fog lamp relay.
Repair Instructions
Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.
* Relay Replacement (Attached to Wire Harness) (See: Power and Ground Distribution/Power Distribution Relay/Service and Repair/Relay
Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (See: Power and Ground Distribution/Power
Distribution Relay/Service and Repair/Relay Replacement (Within an Electrical Center))
* Front Fog Lamp Replacement (Tahoe, Avalanche) (See: Lighting and Horns/Fog/Driving Lamp/Service and Repair/Removal and
Replacement/Front Fog Lamp Replacement (Tahoe, Avalanche))Front Fog Lamp Replacement (Yukon) (See: Lighting and
Horns/Fog/Driving Lamp/Service and Repair/Removal and Replacement/Front Fog Lamp Replacement (Yukon))Front Fog Lamp
Replacement (PLATINUM) (See: Lighting and Horns/Fog/Driving Lamp/Service and Repair/Removal and Replacement/Front Fog Lamp
Replacement (Platinum))
* Control Module References (See: Testing and Inspection/Programming and Relearning) for BCM replacement, setup, and programming
B2540
DTC B2540
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System
Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an
overview of the diagnostic approach.
* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure
Instructions) provides an overview of each diagnostic category.
DTC Descriptors
DTC B2540 02
- Rear Fog Lamp Control Circuit Short to Ground
DTC B2540 05
- Rear Fog Lamp Control Circuit Short to Battery or Open
Diagnostic Fault Information
Circuit/System Description
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