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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 LeSabre 🢒 DTC 🢒 DTC B2628

Circuit Description

The instrument panel (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 feedback voltage to a digital signal and puts it on the class 2 communication bus.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2628 Display Dimming Pulse Width Modulation (PWM) Output Circuit High

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 volts 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 battery positive voltage condition must be corrected.

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 I/P lamps dimmer switch 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: Interior Lights Dimming 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 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 I/P 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 I/P 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 V

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 I/P 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 I/P 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 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