For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC B1372: Device Ignition 1 (ON and START) Circuit Low
DTC B1373: Device Ignition 1 (ON and START) Circuit High
DTC B1382: Device Ignition ACCESSORY Circuit Low
DTC B1383: Device Ignition ACCESSORY Circuit High

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
B+ - Terminal 2 | 1 | 2 | -- | --
Ignition - Terminal 1 | B1382, 3 | B1382 | B1383 | --
Ignition - Terminal 3 | B1372, 3 | B1372 | B1373 | --
Ignition - Terminal 4 | B1442, 3 | B1442, B2957 | B1443 | --
Ignition Voltage - BCM Terminal B7 X1 | 3 | 5 | B1373 | --
Accessory Wakeup Serial Data, BCM Terminal B6 X1 | 3 | 4 | B1383 | --

1. This circuit/condition will cause B+ fuse to the ignition switch to open and will cause a no start condition.
2. No voltage to the Ignition switch.
3. This circuit is a pass through circuit in the BCM, will cause the B+ fuse to the ignition switch to open, and a no start condition.
4. The PCM will not receive accessory voltage from the BCM.
5. The run/crank relay will not energize resulting in multiple systems inoperative.

### Circuit/System Description

The vehicle power mode master (PMM) is the body control module (BCM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination of the power mode. The PMM receives the ignition switch signals, and additionally a reference voltage signal from the BCM, through the ignition switch, and back to the BCM. There are redundancies within the PMM system that can allow operation of certain subsystems when there are faults in the ignition switch circuits. Other information such as serial data input from other modules and DTCs is also used to determine what power mode signals and information is transmitted by the PMM. The BCM logic uses all this information to identify the operator's desired power mode and activate specific discrete signals, and serial data messages for the operation of different subsystems as necessary. Other modules which have switched voltage inputs may operate in a default mode if the PMM serial data message does not match what the individual module can detect from its own connections.

The PMM will activate relays and other direct outputs of the PMM as needed according to the calculated power mode. Some relays controlled by the BCM are switched ignition voltage outputs that are pass through circuits within the BCM directly from the ignition switch. If these circuits short to ground, the B+ circuit fuse to the ignition switch will open.

### Conditions for Running the DTC

B+ is between 9-16 V.

### Conditions for Setting the DTC

#### B1372

The BCM detects that the Run/Crank circuit is open or shorted to ground.

#### B1373

The BCM detects that the Run/Crank signal is shorted to voltage.

#### B1382

The BCM detects that the accessory circuit is open or shorted to ground.

#### B1383

The BCM detects that the accessory circuit is shorted to voltage.

### Actions Taken When the DTC Sets

• | The BCM stores DTC B1372, B1373, B1382, or B1383 in memory.

• | The BCM determines a fail-safe power mode dependent on the last valid power mode detected and the state of the ERF.

### Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

### Diagnostic Aids

The power modes and controls are determined using BCM logic. Comparing the Body Control Module Power Mode data display parameters listed in Circuit/System Verification to the scan tool values of the vehicle will determine if there is a power mode fault.

### Reference Information

#### Schematic Reference

• | Power Distribution Schematics

• | Power Moding Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Power Mode Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

With a scan tool, access BCM, Power Mode data display list and compare all parameters listed with the corresponding ignition key position. The PMM Power Mode Parameters table below illustrates the correct state of these input parameters in correspondence to the ignition switch position. The circuits which the individual parameters are related to are in parentheses.

⇒ | If any parameters are incorrect in any key position, refer to the Circuit/System Testing or Component Testing.

#### PMM Power Mode Parameters

Ignition Switch Position | Ignition Accessory (Terminal 1) | Ignition 1 Run/Crank (Terminal 3) | Ignition Off/Run/Crank (Terminal 4)
--- | --- | --- | ---
OFF | Inactive | Inactive | Active
ACC | Active | Inactive | Inactive
ON | Active | Active | Active
START | Inactive | Active | Active

### Circuit/System Testing

Note: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Connect a test lamp between each fuse test terminal of the ignition switch B+ circuit fuse and ground. The test lamp should illuminate.

⇒ | If the test lamp does not illuminate, test the ignition switch circuits listed below for a short to ground. If all circuits test OK, replace the BCM.

• | B+ terminal 2

• | Ignition terminal 1

• | Ignition terminal 3

• | Ignition terminal 4

2. Disconnect the harness connector at the ignition switch.
3. Connect a test lamp between the B+ circuit terminal 2 and ground. The test lamp should illuminate.

⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

Note: The ignition switch component test must be performed before proceeding with this test to verify the integrity of the switch.

4. Perform the ignition switch component test. Verify the switch passes the test.

⇒ | If the ignition switch does not test normal, replace the ignition switch.

5. Disconnect the X2 harness connector at the BCM, test for less than 1.0 V between the circuit terminals of the BCM listed below and ground:

• | Ignition terminal B7, X2

• | Ignition terminal B8, X2

• | Ignition terminal A14, X2

⇒ | If greater than specified, test the circuit for a short to voltage.

6. Test for less than 1.0 Ω between the BCM and the ignition switch on the circuits listed below:

• | Ignition terminal B7, X2 and 1

• | Ignition terminal B8, X2 and 3

• | Ignition terminal A14, X2 and 4

⇒ | If greater than specified, test the circuit for open/high resistance.

7. If all circuits test normal, replace the BCM.

### Component Testing

#### Ignition Switch

1. Ignition OFF, disconnect the harness connector at the ignition switch.
2. Verify the resistance between the terminals listed below match for each ignition switch position.

⇒ | If not the specified value, replace the ignition switch.

#### Resistance Test

Ignition Switch Position | Terminals 1 and 2 | Terminals 2 and 3 | Terminals 2 and 4 | Terminals 2 and 5 | Terminals 4 and 5
--- | --- | --- | --- | --- | ---
Off Key Out | Infinite | Infinite | Infinite | Infinite | Infinite
Off Key IN | Infinite | Infinite | < 5.0 Ω | Infinite | Infinite
Accessory | < 5.0 Ω | Infinite | Infinite | Infinite | Infinite
Run | < 5.0 Ω | < 5.0 Ω | Infinite | Infinite | < 5.0 Ω
Start | Infinite | < 5.0 Ω | Infinite | Infinite | 250 Ω-10 kΩ

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Ignition and Start Switch Replacement

• | Control Module References for BCM replacement, setup, and programming