GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC C Sierra - 2WD 🢒 Body and Accessories 🢒 Lighting Systems 🢒 Low and High Beams Headlamps Inoperative

Step

Action

Value(s)

Yes

No

1
  1. Turn the ignition OFF.
  2. Connect a scan tool.
  3. Turn the ignition to the ON position.
  4. Using the scan tool, check for any DTCs in the body control module (BCM).

Does the scan tool show any DTCs?

--

Go to Diagnostic System Check - Body Control System in Body Control System

Go to Step 2

2
  1. Turn the headlamp switch to the ON position.
  2. Using the scan tool, read the head lamp relay feedback status.

Does the scan tool show ON?

--

Go to Step 12

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Turn the headlamp switch to AUTO.
  3. Remove and inspect the TBC fuse.

Is the fuse open?

--

Go to Step 4

Go to Step 5

4
  1. Locate and repair the short to ground in CKT 1140 (ORN).
  2. Replace the fuse.

Is the repair complete?

--

System OK

--

5
  1. Reinstall the TBC fuse.
  2. Turn the headlamp switch to the ON position.
  3. Connect a test lamp from LT HDLP or the RT HDLP fuse to ground.

Does the test lamp light?

--

Go to Step 17

Go to Step 6

6
  1. Remove the headlamp relay.
  2. Using a J 35616 , connect a test lamp from terminal 85 of the relay socket to ground.

Does the test lamp light?

--

Go to Step 16

Go to Step 7

7

Connect a test lamp (back probe) from terminal C (WHT wire) at the headlamp switch to ground.

Does the test lamp light?

--

Go to Step 8

Go to Step 9

8

Locate and repair the open in CKT 352 (WHT) between the switch, the BCM and the underhood bussed electrical center (UBEC).

Is the repair complete?

--

System OK

--

9

Connect a test lamp (back probe) from terminal D (ORN wire) at the headlamp switch to ground.

Does the test lamp light?

--

Go to Step 11

Go to Step 10

10

Locate and repair the open in CKT 1140 (ORN) between the UBEC and the switch.

Is the repair complete?

--

System OK

--

11

Replace the headlamp and panel dimmer switch. Refer to Headlamp Switch Replacement .

Is the repair complete?

--

System OK

--

12

Connect a test lamp (back probe) from terminal E13 at the headlamp dimmer switch connector C201C to ground.

Does the test lamp light?

--

Go to Step 13

Go to Step 14

13

Locate and repair the open to ground in CKT 1850 (BLK).

Is the repair complete?

--

System OK

--

14

Connect a test lamp (back probe) from terminal E12 at the headlamp dimmer switch connector C201C to ground.

Does the test lamp light?

--

Go to Step 15

Go to Step 16

15

Replace the headlamp dimmer switch. Refer to Multifunction, Turn Signal, and Hazard Switch Replacement - On Vehicle in Steering Wheel and Column - Tilt.

Is the repair complete?

--

System OK

--

16

Replace the headlamp relay.

Is the repair complete?

--

System OK

--

17

Connect a test lamp (back probe) from terminal E13 at the headlamp dimmer switch connector C201C to ground.

Does the test lamp light?

--

Go to Step 18

Go to Step 19

18
  1. Locate and repair the open to ground in CKT 1850 (BLK).
  2. Locate and repair the open in CKT 352 (WHT) between the BCM and the UBEC.

Is the repair complete?

--

System OK

--

19
  1. Inspect for an open in CKT 524 (PPL) or CKT 525 (YEL) between the headlamps and the headlamp dimmer switch.
  2. If there is no open, replace the headlamp dimmer switch. Refer to Multifunction, Turn Signal, and Hazard Switch Replacement - On Vehicle in Steering Wheel and Column - Tilt.
  3. Locate and repair the open in CKT 352 (WHT) between the BCM and the UBEC.

Is the repair complete?

--

System OK

--