GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Epica 🢒 DTC 🢒 DTC 027-028

Circuit Description

The driver window switch signal circuits provide inputs to the intelligent switching unit (ISU) when the driver window switch is activated to the UP or DOWN position. These inputs allow the ISU to detect a window UP or DOWN request. The ISU provides power and ground to the driver window switch. When the driver window switch is activated to the express DOWN position, power is supplied through the window switch to the signal circuit, which is pulled high. When the ISU detects high voltage on the signal circuit, it will command the window in the DOWN direction. When the switch is pressed again, the command ceases.

Conditions for Setting the DTC
    • The ISU detects an open on a window switch signal circuit.
    • Condition must be present for greater than 20 seconds.

Action Taken When the DTC Sets

Stores a current and history DTC 027 or 028 in ISU memory.

Conditions for Clearing the DTC
    • The ISU no longer detects an open on a window switch circuit.
    • A history DTC will clear after 40 consecutive ignition cycles if the condition for the malfunction is no longer present.

Diagnostic Aids

The following conditions may cause an intermittent malfunction:

    • There is an intermittent open in a window switch signal circuit.
    • A window switch is open internally.

If the DTC does not reset after the code is cleared, then the problem may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections .

Test Description

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

  1. This step tests for the normal state of the window switch.

    2.

  2. This step tests for an open in the window circuit.

Step

Action

Yes

No

Schematic Reference: Moveable Window Schematics

Connector End View Reference: Window Systems Connector End Views

1

Did you perform the Systems Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn OFF the ignition.
  2. Disconnect the intelligent switching unit (ISU).
  3. Connect a test light to the express down circuit at the ISU connector.
  4. Turn ON the ignition, with the engine OFF.
  5. Press the window down switch to express.

Does the scan tool display Inactive?

Go to Step 4

Go to Step 3

Go to Step 3

3

Test the signal circuit of the window switch for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 8

Go to Step 5

4

Inspect for poor connections at the harness connector of the ISU. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 8

Go to Step 6

5

Inspect for poor connections at the harness connector of the window switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 8

Go to Step 7

6

Important: Perform the program procedure for the ISU.

Replace the ISU.

Did you complete the replacement?

Go to Step 8

--

7

Replace the driver window switch.

Did you complete the replacement?

Go to Step 8

--

8
  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