GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2006 🢒 H3 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 Power Mode Mismatch
Table 1: Correct Ignition Switch Inputs and Power Modes

Circuit Description

The body control module (BCM) monitors the ignition inputs Ignition Off/Run/Crank, Ignition 1 Run/Crank and the Ignition Accessory signals supplied from the ignition switch. The BCM uses the sequence that the signals appear, their voltage levels and the engine run flag (ERF) status to determine the power mode. Battery voltage is supplied to the ignition switch by the BATT/IGN/SW fuse in the underhood fuse block. The ignition key resistor signal from the BCM provides a 5-volt supply voltage to the ignition switch. The table below shows the correct ignition switch inputs and power modes.

Correct Ignition Switch Inputs and Power Modes

Ignition Switch Position

BCM Input and Scan Tool Display

Ignition Accessory

Ignition 1 Run/Crank

Ignition Off/Run/Crank

Crank Voltage (Volts)

Power Mode

OFF

Inactive

Inactive

Active
    • 5, w/key in¹
    • 0, w/key out

Off-Awake or RAP

ACC

Active

Inactive

Inactive

0

Accessory

ON

Active

Active

Active

4.4

Run

START

Inactive

Active

Active

1.7-4.2

Crank

¹The correct value should be B+, but the parameter was scaled to maximum 5 volts, to increase reading accuracy in the lower range.

Step

Action

Yes

No

    • Schematic Reference: Body Control System Schematics
    • Schematic Reference: Power Distribution Schematics in Wiring Systems
    • Connector End View Reference: Computer/Integrating Systems Connector End Views

DEFINITION: This table is used if the observed vehicle power mode does not match the ignition switch position.

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

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

  1. With a scan tool, under the Diagnostic Circuit Check menu observe the Class 2 Power Mode parameter.
  2. Turn the ignition to all positions and compare the parameter to the correct ignition switch inputs table above.

Does the scan tool display the correct power mode?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

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

  1. Observe the Crank Voltage parameter with the scan tool.
  2. Turn the ignition to all positions and compare the parameter to the values from the table above.
  3. Observe the Ignition Off/Run/Crank parameter with the scan tool.
  4. Turn the ignition to all positions and compare the parameter to the correct ignition switch inputs table above.

Do the voltage displayed for Crank Voltage and the Ignition Off/Run/Crank signal match the values from the table above?

Go to Step 4

Go to DTC B1441, B1442, or B1443 and use that procedure to diagnose the concern

4

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

  1. Observe the Ignition 1 Run/Crank parameter with the scan tool.
  2. Turn the ignition to all positions and compare the parameter to the correct ignition switch inputs table above.

Does the Ignition 1 Run/Crank signal display correctly?

Go to Step 5

Go to DTC B1372, B1373, or B1374 and use that procedure to diagnose the concern

5

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

  1. Observe the Ignition Accessory parameter with the scan tool.
  2. Turn the ignition to all positions and compare the parameter to the correct ignition switch inputs table above.

Does the Ignition Accessory signal display correctly?

Go to Step 6

Go to DTC B1382, B1383, or B1384 and use that procedure to diagnose the concern

6
  1. Disconnect the body control module (BCM).
  2. Inspect for poor connections and terminal tension at the harness connector of the BCM. 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

7

Replace the BCM. Refer to Computer/Integrating Systems Connector End Views for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 8

--

8

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