GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 LeSabre 🢒 Body and Accessories 🢒 Lighting Systems 🢒 DTC B2642 Delayed Exterior Lighting Ctrl CKT Low

Object Number: 425364 Size: MF
Dimmer Control
Handling ESD Sensitive Parts Notice
Lighting Systems Components
Headlamp Switch, Ambient Light Sensor (C67)

Circuit Description

The twilight rheostate sensor is a potentiometer. The climate control panel (CCP) determines the control setting based on the voltage from the twilight rheostate sensor. The CCP controls the headlamps automatic on/off and delayed off functions.

Conditions for Running the DTC
    • Enable flag is set to enable.
    • The CCP is powered.

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

Action Taken When the DTC Sets

Twilight status set to ON.

Conditions for Clearing the MIL/DTC

The heater and A/C 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. Tests for the proper operation of the circuit in the high voltage range.

    2.

  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 signal circuit is shorted to voltage.

    3.

  3. Tests for a short to ground in the 5 volt reference circuit.

Step

Action

Value(s)

Yes

No

1

Did you perform the Lighting Systems Diagnostic System Check?

--

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. Position the IP dimmer switch lever to the LO position.
  4. With a scan tool, observe the Twilight Delay Pot data parameter in the climate control panel (CCP) 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 signal circuit of the twilight delay switch and the sensors return 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 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 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 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 signal circuit of the twilight delay switch for a short to 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 sensors return 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

--

14

Replace the CCP. Refer to Control Assembly Replacement in HVAC Systems with A/C - Manual.

Did you complete the replacement?

--

Go to Step 15

--

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