GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 LeSabre 🢒 Restraints 🢒 SIR 🢒 DTC B2642

Circuit Description

The twilight delay switch is a potentiometer. The HVAC control module determines the control setting based on the voltage from the twilight delay switch. The HVAC control module controls the headlamps automatic on/off and delayed off functions.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2642 Delayed Exterior Lighting Control Circuit Low

Conditions for Running the DTC
    • The enable flag is set to enable.
    • The HVAC control module is powered.

Conditions for Setting the DTC
    • The twilight delay switch voltage is less than 0.2 volts.
    • The above condition is present for greater than 2 seconds.

Action Taken When the DTC Sets

Twilight status is set to ON.

Conditions for Clearing the DTC

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

Test Description

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

  1. This step tests for the proper operation of the circuit in the high voltage range.

    2.

  2. This step 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 signal circuit is shorted to battery positive voltage.

    3.

  3. This step tests for a short to ground in the 5-volt reference circuit.

Step

Action

Value(s)

Yes

No

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

Connector End View Reference: Computer/Integrating Systems Connector End Views in Computer/Integrating Systems or Lighting Systems Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Position the instrument panel (I/P) dimmer switch lever to the minimum position.
  4. With a scan tool, observe the Twilight Delay Pot data parameter in the climate control panel (CCP) Open/Short data list.

Does the scan tool indicate that the Twilight Delay Pot 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 headlamp switch.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Twilight Delay Pot data parameter.

Does the scan tool indicate that the Twilight Delay Pot data parameter is greater than the specified value?

4.8 V

Go to Step 4

Go to Step 8

4

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the twilight sentinel delay signal circuit of the twilight delay switch and the low reference circuit of the twilight delay switch.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Twilight Delay Pot data parameter.

Does the scan tool indicate that the Twilight Delay Pot data parameter is less than the specified value?

0.2 V

Go to Step 5

Go to Step 9

5

  1. Turn OFF the ignition.
  2. Disconnect the fused jumper wire.
  3. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the twilight delay switch and the twilight sentinel delay signal circuit of the twilight delay switch.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, observe the Twilight Delay Pot data parameter.

Does the scan tool indicate that the Twilight Delay Pot data parameter is greater than the specified value?

4.8 V

Go to Step 7

Go to Step 6

6

Test the 5-volt reference circuit of the twilight delay switch 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 15

Go to Step 12

7

Test the 5-volt reference circuit of the twilight delay switch 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 15

Go to Step 11

8

Test the twilight sentinel delay signal circuit of the twilight delay switch 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 15

Go to Step 12

9

Test the twilight sentinel delay signal circuit of the twilight delay switch 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 15

Go to Step 10

10

Test the low reference circuit of the twilight delay switch for 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 15

Go to Step 12

11

Inspect for poor connections at the harness connector of 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 13

12

Inspect for poor connections at the harness connector of the 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 15

Go to Step 14

13

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

Did you complete the replacement?

--

Go to Step 15

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14

Replace the CCP. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 15

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15
  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