GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

Important: A short to ground will cause an open fuse(s). Before performing this diagnostic procedure, inspect the fuse(s) for an open.

1

Disconnect the turn/headlamp switch assembly connector C1.

Do the headlamps go out?

--

Go to Step 2

Go to Step 3

2

  1. Use a DMM in order to measure the resistance between terminal 33 and terminal 35 of the turn/headlamp switch assembly.
  2. Use a DMM in order to measure the resistance between terminal 34 and terminal 35 of the turn/headlamp switch assembly.

Is the measured resistance equal to the specified value?

Go to Step 4

Go to Step 5

3

Disconnect connector C3 of the underhood junction block.

Do the headlamps go out?

--

Go to Step 6

Go to Step 7

4

Use a DMM in order to measure the resistance between terminal 36 and terminal 35 of the turn/headlamp switch assembly.

Is the measured resistance within the specified range?

Go to Step 10

Go to Step 5

5

Replace the turn/headlamp switch assembly. Refer to Multifunction Turn Signal Lever Replacement - On Vehicle in Steering Wheel and Column-Standard

Is the repair complete?

--

Go to Daytime Running Lights (DRL) System Check

--

6

Repair the short to ground in CKT 1200 (high beams on) or CKT 1201 (low beams on) between the underhood junction block and the turn/headlamp switch assembly. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Daytime Running Lights (DRL) System Check

--

7

Disconnect connector C2 of the underhood junction block.

Do the headlamps go out?

--

Go to Step 8

Go to Step 9

8

Replace the underhood junction block. Refer to Underhood Fuse Block Replacement in Engine Electrical.

Is the repair complete?

--

Go to Daytime Running Lights (DRL) System Check

--

9

Repair the short to ground in CKT 1200 (high beams on) or CKT 1201 (low beams on) between the underhood junction block and the remaining lit lamp. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Daytime Running Lights (DRL) System Check

--

10

Disconnect the automatic lamp control (ALC) relay.

Do the headlamps go out?

--

Go to Step 11

Go to Step 12

11

Replace the ALC relay.

Is the repair complete?

--

Go to Daytime Running Lights (DRL) System Check

--

12

Disconnect connector C3 of the underhood junction block.

Do the headlamps go out?

--

Go to Step 8

Go to Step 13

13

Repair the short to battery positive voltage in CKT 306 between the underhood junction block and the turn/headlamp switch assembly. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Daytime Running Lights (DRL) System Check

--