GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 Body and Accessories 🢒 Lighting Systems 🢒 Headlamps Inoperative in Low Light Conditions

Step

Action

Value(s)

Yes

No

Schematic Reference: Headlights Schematics

1

Did you perform the Lighting Systems Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2
  1. Turn the headlamp switch to the AUTO position.
  2. Turn ON the ignition, with the engine OFF.
  3. Cover and uncover the ambient light sensor.

Does the system operate normally?

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Go to Testing for Electrical Intermittents in Wiring Systems

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Turn the headlamps to the ON position.

Do the headlamps come on?

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Go to Step 4

Go to Low and High Beams Headlamps Inoperative

4

With the scan tool, read the head lamp relay feedback status in the BCM.

Does the scan tool show the status of ON?

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Go to Step 6

Go to Step 5

5
  1. Turn the headlamp switch to the AUTO position.
  2. Turn OFF the ignition.
  3. Disconnect the BCM.
  4. Turn ON the headlamp switch.
  5. Connect a test lamp between the headlamp relay coil supply voltage circuit of the BCM and a good ground.

Does the test lamp illuminate?

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Go to Step 6

Go to Step 11

6
  1. Reconnect the BCM if the BCM was disconnected in a previous step.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, read the ambient light sensor voltage in the BCM.
  4. While monitoring the scan tool, cover the ambient light sensor, then induce a light source to the sensor.

Does the sensor voltage vary near the specified values?

4.7-2.2 V (DRL on)

0.2-1.3 V (Headlamps on)

Go to Step 7

Go to Step 9

7
  1. Ensure the headlamp switch is in the auto position.
  2. With the scan tool, command the headlamps ON.

Do the headlamps come on?

--

Go to Step 10

Go to Step 8

8

Inspect for poor connections at the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 15

Go to Step 12

9

Inspect for poor connections at the ambient light sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

10

Inspect for poor connections at the headlamp switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

11

Repair the open in the headlamp relay coil supply voltage circuit between the engine wiring harness junction block and the BCM. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

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Go to Step 15

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12

Important: Perform the setup procedure for the BCM.

Replace the BCM. Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

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Go to Step 15

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13

Replace the ambient light sensor. Refer to Ambient Light Sensor Replacement .

Did you complete the replacement?

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Go to Step 15

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14

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

Did you complete the replacement?

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Go to Step 15

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15

Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 3