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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Sonoma Pickup - 4WD 🢒 Body and Accessories 🢒 Body Control System 🢒 Power Mode Mismatch

Circuit Description

Normal vehicle class 2 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 the power mode master (PMM) module in order to determine the correct power mode. The PMM communicates the system power mode to all class 2 modules on the class 2 serial data line. 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 signal circuits that are not required.

    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

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 4

2
  1. Turn ON the ignition, 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 3

Go to Step 4

3

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 Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 4

4

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

Is voltage present on only the inputs specified for the ignition switch position?

Go to Step 5

Go to Step 6

5

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 test lamp 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 any inputs specified for the ignition switch position?

Go to Step 7

Go to Step 9

6

  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 12

Go to Step 8

7

  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 12

Go to Step 8

8

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 12

Go to Step 10

9

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 12

Go to Step 11

10

Replace the ignition switch. Refer to Ignition Switch Replacement - On Vehicle in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 12

--

11

Important:: After replacement of the PMM perform the set up procedure if required.

Replace the PMM. Refer to Control Module References .

Did you complete the replacement?

Go to Step 12

--

12

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

  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