GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Did you perform the Lighting Systems Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

Verify that the fog lamps are inoperative.

Do the fog lamps operate normally?

--

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Use the Scan Tool to inspect for the following related Body Control Module (BCM) Data/ Input parameters and Output controls.

Refer to Scan Tool Data List in Body Control System for typical values and definitions.

    • Headlamp Ambient Light Sensor
    • Park Brake Switch
    • Auto Headlamps
    • Headlamp Relay Feedback
    • Headlamp Power Relay
    • Park Lamp Relay
    • Rear Fog Lamp Relay
    • Rear Fog Lamp Switch
    • Park Lamps

Did you find and correct a problem?

--

Go to Step 18

Go to Step 4

4

With the engine Off, turn the key to RUN and the Headlamp Switch to HEAD.

Are the marker lamps on?

--

Go to Step 5

Go to Marker Lamps Inoperative

5

Inspect the FOG LP 15A fuse in the Underhood Fuse Block.

Is the fuse open?

--

Go to Step 6

Go to Step 9

6

Remove the Fog Lamp Relay.

Using a J 39200 Digital Multimeter (DMM), check for continuity to ground at terminal 3 of the Fog Lamp Relay connector in the Underhood Fuse Block. Refer to Circuit Testing in Wiring Systems.

Is continuity present?

--

Go to Step 7

Go to Step  8

7

Locate and Repair the short to ground in the associated circuit feeding the FOG LP 15A fuse. Refer to

B+ Bus Bar


Object Number: 548924  Size: FS
Power and Grounding Components
Ign START, RUN and ACC Bus Bar
G104, G106, G107, G108 and G118
in Wiring Systems for further diagnosis.

Is the repair complete?

--

Go to Step 18

--

8

Locate and Repair the short to ground in CKT 34 (PPL). Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 18

--

9

Turn the Fog Lamp Switch to the ON position.

Use the J 39200 DMM to check for the specified voltage of CKT 34 (PPL) at either of the Fog Lamp sockets. Refer to Circuit Testing in Wiring Systems.

Is the specified voltage present?

B+

Go to Step 10

Go to Step 11

10

Locate and repair the open or high resistance in CKT 1350 (BLK). Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 18

--

11

Use the Scan Tool to monitor the Fog Lamp Switch ON input.

Does the scan tool indicate that the switch is ON?

--

Go to Step 12

Go to Step 15

12

Test CKT 34 (PPL) and CKT 1977 (YEL) for opens or high resistance. Refer to Circuit Testing in Wiring Systems.

Was a problem found?

--

Go to Step 13

Go to Step 14

13

Locate and repair the open or high resistance in CKT 34 (PPL) or CKT 1977 (YEL). Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 18

--

14

Replace the Fog Lamp Relay. Refer to Fog Lamp Relay Replacement .

Is the repair complete?

--

Go to Step 18

--

15

Test CKT 187 (LT BLU) and CKT 1850 (BLK) for opens or high resistance. Refer to Circuit Testing in Wiring Systems.

Was a problem found?

--

Go to Step 16

Go to Step 17

16

Locate and repair the open or high resistance in CKT 187 (LT BLU) and CKT 1850 (BLK). Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 18

--

17

Replace the Fog Lamp Switch. Refer to Rear Fog Lamp Switch Replacement .

Is the repair complete?

--

Go to Step 18

--

18

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3