GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Bonneville 🢒 Body and Accessories 🢒 Lighting Systems 🢒 DTC B2627

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 feedback 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 less than 0.2 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 ground 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 signal circuit is shorted to voltage.

    3.

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

    4.

  4. Tests for a short to ground in the twilight sentinel delay signal circuit of the twilight delay switch. A short to ground may set DTC B2627 and DTC B2642 depending position of the I/P dimmer switch.

Step

Action

Value(s)

Yes

No

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

Connector End View Reference: Master Electrical Component List in Wiring Systems

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. Turn the twilight delay switch to the OFF position.
  4. With a scan tool, observe the Interior Dim Pot data parameter in the climate control panel (CCP) Open/Short data list.
  5. Move the I/P dimmer switch from the minimum position to the maximum position.

Does the scan tool indicate that the Interior Dim Pot data parameter stays 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 fog lamp 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 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 16

Go to Step 13

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 16

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 16

Go to Step 13

9

Test the instrument panel lamps dimmer switch signal 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 16

Go to Step 10

10

Test the ground 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 16

Go to Step 13

11

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 16

Go to Step 12

12

Inspect for poor connections at the harness connector of the fog lamp 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 16

Go to Step 14

13

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 16

Go to Step 15

14

Replace the fog lamp switch. Refer to Fog Lamp Switch Replacement .

Did you complete the replacement?

--

Go to Step 16

--

15

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

Did you complete the replacement?

--

Go to Step 16

--

16
  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