GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The sunload sensor assembly is a light sensitive photocell. The HVAC control module determines the ambient light based on the voltage from the sunload sensor assembly. The HVAC control module controls the head lamp automatic ON/OFF and delayed OFF functions.

Conditions for Running the DTC

    • Enable flag is set to enable.
    • DTC B1327 is not current.
    • The HVAC control module is powered.

Conditions for Setting the DTC

    • The sunload sensor assembly voltage is less than 0.2 volts.
    • The above condition is present for greater than 2 seconds.

Action Taken When the DTC Sets

    • The HVAC control module sets the variable ambient light status is set to DARK.
    • The HVAC control module sets a DTC.

Conditions for Clearing the DTC

The HVAC control module does not detect a voltage less than the predetermined value during the diagnostic self test.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Tests for the proper operation of the circuit in the high voltage range.

  2. Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the twilight sentinel delay signal circuit is shorted to battery positive voltage.

Step

Action

Value(s)

Yes

No

Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference: Body Control System Connector End Views or Lighting Systems Connector End Views

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. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the Ambient Light Sensor data parameter in the climate control panel (CCP) Open/Short data list.

Does the scan tool indicate that the ambient light sensor data parameter is within the specified range?

0.2-4.8 V

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the sunload sensor assembly.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Ambient Light Sensor data parameter.

Does the scan tool indicate that the ambient light sensor data parameter is greater than the specified value?

4.8 V

Go to Step 4

Go to Step 5

4

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the ambient light sensor signal circuit of the sunload sensor assembly and the low reference circuit of the sunload sensor assembly.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Ambient Light Sensor data parameter.

Does the scan tool indicate that the Ambient Light Sensor data parameter is less than the specified value?

0.2 V

Go to Step 8

Go to Step 6

5

Test the twilight sentinel delay signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

6

Test the ambient light sensor signal circuit for a short to battery positive voltage, a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 7

7

Test the low reference circuit for high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

8

Inspect for poor connections at the harness connector of the sunload sensor assembly. 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 12

Go to Step 10

9

Inspect for poor connections at the harness connector of the HVAC control module (CCP). 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 12

Go to Step 11

10

Replace the sunload sensor assembly. Refer to Sunload and Twilight Sentinel Sensor Replacement in Instrument Panel, Gages and Console.

Did you complete the replacement?

--

Go to Step 12

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11

Replace the HVAC control module (CCP). Refer to HVAC Control Module Replacement in HVAC Systems - Manual.

Did you complete the replacement?

--

Go to Step 12

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12

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK