SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 533 (LIGHTING SYSTEMS)DIAGNOSTIC INFORMATION AND PROCEDURESCOURTESY LAMPS ALWAYS ON
1999 GMC Forward Control 5.7 R, Automatic

Courtesy Lamps Always On

1999 GMC Forward Control 5.7 R, AutomaticSECTION Courtesy 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.
Courtesy Lamps Always On

Step Action Yes No
Schematic Reference: Interior 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. Close all the doors and turn the I/P dimmer switch to the OFF position.
Are the courtesy lamps OFF?		 Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems Go to Step 3 
3
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the Courtesy Lamp Switch Input circuit status.
Is the Courtesy Lamp Switch Input circuit ON?		 Go to Step 4  Go to Step 5 
4
  1. Disconnect the headlamp switch connector.
  2. With a scan tool, observe the Courtesy Lamp Switch Input circuit status.
Is the Courtesy Lamp Switch Input circuit ON?		 Go to Step 9  Go to Step 13 
5 With a scan tool, observe the Driver Door Open Switch Input circuit status.
Is the Driver Door Open Switch Input circuit active?		 Go to Step 6  Go to Step 7 
6
  1. Disconnect the LF door latch connector.
  2. With a scan tool, observe the Driver Door Open Switch Input circuit status.
Is the Courtesy Lamp Switch Input circuit active?		 Go to Step 10  Go to Step 14 
7 With a scan tool, observe the Rear, Passenger and Lift Gate Door Open Switches Input circuits status.
Is the Door Open Switches Input circuits active?		 Go to Step 8  Go to Step 12 
8
  1. Disconnect each door latch connector one at time.
  2. With a scan tool, observe the Door Open Input circuit status as each door lock connector is disconnected.
Does the Courtesy Lamp Switch Input circuit turn inactive when the door latch connectors are disconnected?		 Go to Step 15  Go to Step 11 
9 Test for a short to ground on the courtesy lamps switch signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 17  Go to Step 16 
10 Test for a short to ground on the driver door open switch input circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 17  Go to Step 16 
11 Test for a short to ground on the open door switch input circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 17  Go to Step 16 
12 Test for a short to ground in the courtesy lamps control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 17  Go to Step 16 
13 Replace the headlamp switch. Refer to Headlamp Switch Replacement .
Did you complete the repair?		 Go to Step 17  -
14 Replace the drivers door latch switch. Refer to Lock Replacement - Rear Door in Doors.
Did you complete the repair?		 Go to Step 17  -
15 Replace the inoperative door latch switch. Refer to Lock Replacement - Rear Door or Lock Replacement - Front Door in Doors or Latch Replacement - Liftgate (Aztek) in Body Rear End.
Did you complete the repair?		 Go to Step 17  -
16
IMPORTANT: Perform the set up procedures for the Body Control Module (BCM). Refer to Body Control Module (BCM) Programming/RPO Configuration .
Replace the BCM. Refer to Body Control Module Replacement in Body Control Systems.Did you complete the repair?		 Go to Step 17  -
17 Operate the system in order to verify the repair.
Did you correct the condition?		 System OK Go to Step 2 
RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

Shop Manual-Ready ToolsFree Quote CheckQuote Shield Pro

When to See a Mechanic

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

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • 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.