GM Service Manual Online
For 1990-2009 cars only

Diagnostic Aids

If there are several other systems inoperative with the ignition ON, such as power windows, power seats, sunroof, and front turn signals, check ground G101.

Step

Action

Values

Yes

No

1

Inspect fuses F12, EF16, EF14, EF10 and EF13.

Are any fuses open?

--

Go to Step 2

Go to Step 3

2

  1. Inspect for a short circuit and repair it, if necessary.
  2. Replace the open fuse.

Is the repair complete?

--

System OK

--

3

Use a voltmeter to measure the voltage at F12.

Does the voltage measure within the specified range?

11-14 V

Go to Step 5

Go to Step 4

4

Repair the open power supply circuit to fuse EF12.

Is the repair complete?

--

System OK

--

5

Turn the headlamps ON.

Are the parking lamps, tail lamps, and license lamps working?

--

Go to Step 6

Go to Step 8

6

Temporarily substitute the illumination relay in place of the headlamp relay.

Do the headlamps operate with the substituted relay?

--

Go to Step 7

Go to Step 8

7

  1. Reinstall the illumination relay in its original position.
  2. Replace the headlamp relay.

Is the repair complete?

--

System OK

--

8

  1. Disconnect the headlamp connectors, and use an ohmmeter to check continuity between terminal B and ground. Repeat this procedure on the other side.
  2. Connect the headlamp connectors.

Does the ohmmeter indicate the specified value between each terminal and ground?

0 ohms

Go to Step 10

Go to Step 9

9

Repair the open circuit between the headlamps and ground.

Is the repair complete?

--

System OK

--

10

  1. Disconnect light switch connector.
  2. Turn the headlamps ON.
  3. Using a voltmeter, measure voltage at light switch connector terminal 3, harness side.

Is the voltage within the specified range?

11-14 V

Go to Step 12

Go to Step 11

11

Repair the open circuit between the light relay and the light switch.

Is the repair complete?

--

System OK

--

12

Use an ohmmeter to check continuity between light switch connector, terminal 2 harness side, and ground.

Did the ohmmeter indicate the specified value?

0 ohms

Go to Step 14

Go to Step 13

13

Repair the open circuit between light switch connector and ground.

Is the repair complete?

--

System OK

--

14

Replace the light switch.

Is the repair complete?

--

System OK

--