GM Service Manual Online
For 1990-2009 cars only

Headlamps - Low Beams On with Headlamp Switch Off DRL Off

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 or CKT 718 (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

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/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 connection OK?

--

Go to Step 16

Go to Step 17

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

--

16

Replace the DRL series dropping resistor.

Is the repair complete?

--

System OK

--

17

Repair the connection.

Is the repair complete?

System OK

--

Headlamps - Low Beams On with Headlamp Switch Off During DRL Operation

Step

Action

Value(s)

Yes

No

1

  1. Disconnect the lighting relay.
  2. Backprobe the headlamp switch with a test lamp from terminal 4 to B+.

Did the test lamp light?

--

Go to Step 2

Go to Step 3

2

Inspect for a short to ground in CKT 717 (RED/BLK) between the lighting relay and the headlamp switch.

Does a short to ground exist?

--

Go to Step 4

Go to Step 5

3

  1. Connect the lighting relay.
  2. Disconnect the DRL series dropping register.
  3. Start the engine.
  4. Disengage the park brake.

Are the headlamps lit?

--

Go to Step 6

Go to Step 7

4

Repair the short to ground in CKT 717 (RED/BLK) between the lighting relay and the headlamp switch.

Is the repair complete?

--

System OK

--

5

Replace the headlamp switch.

Is the repair complete?

--

System OK

--

6

Inspect for a short to ground in CKT 715 (RED/YEL) between the lighting relay and the DRL series dropping register.

Does a short to ground exist?

--

Go to Step 8

Go to Step 9

7

Replace the DRL series dropping resistor.

Is the repair complete?

--

System OK

--

8

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

Is the repair complete?

--

System OK

--

9

Replace the lighting relay.

Is the repair complete?

--

System OK

--