GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Disconnect the headlamp switch.

Did the headlamps turn off?

--

Go to Step 3

Go to Step 2

2

Backprobe the lighting relay with a test lamp from terminal 86 to B+.

Did the test lamp light?

--

Go to Step 4

Go to Step 5

3

Replace the headlamp switch.

Is the repair complete?

--

System OK

--

4

Repair the short to ground in CKT 717, 718 or 722 (RED/BLK) between the headlamp switch, diode module 2, and the lighting relay.

Did the headlamps turn off?

--

System OK

--

5

Disconnect the lighting relay.

Did the headlamps turn off?

--

Go to Step 6

Go to Step 7

6

Connect a test lamp from lighting relay connector terminal 87A to B+.

Did the test lamp light?

--

Go to Step 8

Go to Step 9

7

Repair the short to ground in CKT 691 or CKT 697 (RED/BLK) between the left headlamp, the right headlamp, and the lighting relay.

Is the repair complete?

--

System OK

--

8

Connect the lighting relay and disconnect the DRL Off relay.

Did the headlamps turn off?

--

Go to Step 10

Go to Step 11

9

Replace the lighting relay.

Is the repair complete?

--

System OK

--

10

Replace the DRL Off relay.

Is the repair complete?

--

System OK

--

11

Disconnect the DRL On relay.

Did the headlamps turn off?

--

Go to Step 12

Go to Step 13

12

Repair the short to ground in CKT 741 (BLK/DK GRN) between the DRL Off relay and the DRL On relay.

Is the repair complete?

--

System OK

--

13

Disconnect the DRL series dropping resistor.

Did the headlamps turn off?

--

Go to Step 14

Go to Step 15

14

Inspect for a short to ground in CKT 729 (RED/BLK) between the DRL series dropping resistor and the DRL on relay.

Is the repair complete?

--

System OK

--

15

Repair the short to ground in CKT 715 (RED/YEL) between the lighting relay and the DRL series dropping resistor.

Is the repair complete?

--

System OK

--