GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2003 🢒 LeSabre 🢒 DTC 🢒 DTC B2628

Circuit Description

The I/P dimmer switch is a potentiometer. It is powered by the HVAC control module. The HVAC control module determines the level of dimming desired based on the voltage from the I/P dimmer switch. The HVAC control module converts the I/P dimmer switch feed back voltage to a digital signal and puts it on the Class II communication bus.

Conditions for Running the DTC

The HVAC control module must be powered.

Conditions for Setting the DTC

The feedback voltage is greater than 4.8 V for more than 200 milliseconds.

Action Taken When the DTC Sets

The dimming level is set to full brightness for all displays.

Conditions for Clearing the DTC

The I/P dimmer switch short to voltage condition must be corrected.

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 instrument panel lamps dimmer switch signal circuit is shorted to battery positive voltage.

    3.

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

Step

Action

Value(s)

Yes

No

Schematic Reference: Interior Lights Dimming 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. Position the I/P dimmer switch to the HI position.
  4. Position the twilight delay switch to the OFF position.
  5. With a scan tool, observe the Interior Dim Pot data parameter in the climate control panel (CCP) Open/Short data list.

Does the scan tool indicate that the Interior Dim 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 Interior Dim Pot data parameter.

Does the scan tool indicate that the Interior Dim 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 instrument panel lamps dimmer switch signal circuit of the I/P dimmer switch and the low reference circuit of the I/P dimmer switch.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Interior Dim Pot data parameter.

Does the scan tool indicate that the Interior Dim 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 I/P dimmer switch and the instrument panel lamps dimmer switch signal circuit of the I/P dimmer switch.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, observe the Interior Dim Pot data parameter.

Does the scan tool indicate that the Interior Dim Pot data parameter is greater than the specified value?

4.8 

Go to Step 7

Go to Step 6

6

Test the 5-volt reference circuit of the I/P dimmer 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 I/P dimmer 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 instrument panel lamps dimmer switch signal circuit of the I/P dimmer 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 instrument panel lamps dimmer switch signal circuit of the I/P dimmer 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 I/P dimmer 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 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 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 HVAC control module (CCP). Refer to HVAC Control Module Replacement in HVAC Systems - Manual.

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