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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Terraza - 4WD 🢒 Engine 🢒 Engine Electrical 🢒 Power Mode Mismatch

Circuit Description

Normal vehicle serial data communications and module operations will not begin until the system power mode has been identified. Discrete wires from the ignition switch contacts are monitored by a module which acts as the power mode master (PMM) in order to determine the correct power mode. The module which is the PMM communicates the system power mode to all modules on the serial data lines. Refer to Body Control System Description and Operation to identify which module is the PMM and the applicable power mode look up table.

Test Description

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

  1. This step tests for battery voltage on the incorrect signal circuits.

    2.

  2. This step tests for no battery voltage on the required signal circuits.

    3.

  3. If any ignition switch parameters that should be inactive in the present ignition switch position are active, 2 ignition switch signal circuits may be shorted together.

    4.

  4. This step eliminates open circuits as the cause of the malfunction.

Step

Action

Yes

No

Schematic Reference: Body Control System Schematics

Connector End View Reference: Computer/Integrating Systems Connector End Views and Master Electrical Component List in Wiring Systems

Important: Open the driver door and leave it open during this test. This will disable the retained accessory power (RAP) mode and eliminate this power mode from the power mode parameter list.

1
  1. Install a scan tool.
  2. Turn OFF the ignition.
  3. With a scan tool, under the Diagnostic Circuit Check menu observe the Class 2 Power Mode parameter.

Does the displayed power mode parameter match the actual ignition switch position?

Go to Step 2

Go to Step 6

2
  1. Turn the ignition switch to the UNLOCK position.
  2. With a scan tool, under the Diagnostic Circuit Check menu observe the Class 2 Power Mode parameter.

Does the displayed power mode parameter match the actual ignition switch position?

Go to Step 3

Go to Step 6

3
  1. Turn the ignition switch to the RUN position, with the engine OFF.
  2. With a scan tool, under the Diagnostic Circuit Check menu observe the Class 2 Power Mode parameter.

Does the displayed power mode parameter match the actual ignition switch position?

Go to Step 4

Go to Step 6

4

Important:: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.

  1. Turn the ignition switch to the CRANK position.
  2. With a scan tool, under the Diagnostic Circuit Check menu observe the Class 2 Power Mode parameter.

Does the displayed power mode parameter match the actual ignition switch position?

Go to Step 5

Go to Step 6

5
  1. Turn the ignition switch to the ACCY position.
  2. With a scan tool, under the Diagnostic Circuit Check menu observe the Class 2 Power Mode parameter.

Does the displayed power mode parameter match the actual ignition switch position?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 6

6

Important:: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.

  1. Turn OFF the ignition.
  2. Disconnect the power mode master (PMM).
  3. Hold the ignition switch in the position that indicated the incorrect power mode.
  4. With a DMM attached to a good ground, test all the PMM ignition switch inputs for positive voltage. Refer to Body Control System Description and Operation for the state of the input circuits at a specified ignition switch position.

Is voltage present on only the inputs selected by the ignition switch position?

Go to Step 7

Go to Step 8

7

Important:: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.

  1. Hold the ignition switch in the position that indicated the incorrect power mode.
  2. With a DMM attached to a good ground, test the PMM ignition switch inputs for voltage. Refer to Body Control System Description and Operation .

Is voltage not present on only inputs specified for the ignition switch position?

Go to Step 9

Go to Step 11

8

  1. Disconnect the ignition switch.
  2. Test the PMM ignition switch input circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
  3. Test the PMM ignition switch circuits for a short between circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 10

9

  1. Disconnect the ignition switch.
  2. Test the PMM ignition switch input circuits for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 10

10

Inspect for poor connections and terminal tension at the harness connector of the ignition 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 14

Go to Step 12

11

Inspect for poor connections and terminal tension at the harness connector of the PMM. 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 14

Go to Step 13

12

Replace the ignition switch. Refer to Ignition and Start Switch Replacement in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 14

--

13

Replace the PMM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 14

--

14
  1. Reconnect all disconnected components.
  2. With a scan tool, under the Diagnostic Circuit Check menu observe the Class 2 Power Mode parameter.
  3. Cycle the ignition switch through all possible positions one at a time.

Does the displayed power mode parameter match the actual ignition switch position?

System OK

Go to Step 1