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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 533 (LIGHTING SYSTEMS)DIAGNOSTIC INFORMATION AND PROCEDURESFOG LAMPS ALWAYS ON
1999 GMC Forward Control 5.7 R, Automatic

Fog Lamps Always On

1999 GMC Forward Control 5.7 R, AutomaticSECTION Fog Lamps Always On
WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
Fog Lamps Always On

Step Action Yes No
Schematic Reference: Fog Lights Schematics 
Connector End View Reference: Master Electrical Component List in Wiring Systems.
1 Did you perform the Lighting System Diagnostic System Check? Go to Step 2  Go to Diagnostic System Check - Lighting Systems 
2
  1. Turn the ignition to the ON position.
  2. Press the fog lamp switch to the OFF position.
Are the fog lamps OFF?		 Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems Go to Step 3 
3 Remove the fog lamp relay.
Do the fog lamps turn OFF?		 Go to Step 6  Go to Step 4 
4
  1. Reinstall the fog lamp relay.
  2. Test for a short to battery positive voltage on the fog lamp relay switched battery positive voltage supply circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 8  Go to Step 7 
5 Test for a short to ground in the fog lamp switch signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 8  Go to Step 6 
6 Replace the fog lamp relay. Refer to Relay Replacement (Attached to Wire Harness) or Relay Replacement (Within an Electrical Center) in Wiring Systems.
Did you complete the replacement?		 Go to Step 8  -
7 Replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems.
Did you complete the replacement?		 Go to Step 8  -
8 Operate the system in order to verify the repair.
Did you correct the condition?		 System OK Go to Step 2 
RENDER: 1.0x

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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
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  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.