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

### 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 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 a fuse in the underhood fuse block. The Run/Crank voltage circuit energizes the Run/Crank relay and is a pass through circuit in the BCM.

### 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.

### Action Taken when the DTC Sets

• | The BCM stores DTC B1372 or B1373 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.

• | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

### 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

#### 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, observe the Ignition 1 Run/Crank parameter and compare the parameter to the Correct Ignition Switch Inputs table with the corresponding ignition key position. The Correct Ignition Switch Inputs table illustrates the correct state of these input parameters (circuits) in correspondence to the ignition switch position.

#### 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

1. Inspect for an open B+ fuse to the ignition switch. The fuse should be OK.

⇒ | If the fuse is open, test the following circuits for a short to ground, if all circuits test OK, replace the BCM.

• | B+ to the ignition switch

• | Accessory voltage (ignition switch output)

• | Run/Crank voltage (ignition switch output)

• | Accessory voltage (BCM output)

• | Run/Crank voltage (BCM output)

2. Disconnect the harness connector at the ignition switch.
3. Verify that a test lamp illuminates between ground and the B+ circuit terminal 2 and ground.

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

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

4. Perform the ignition switch component test. The test should pass.

⇒ | If the ignition switch fails, replace the ignition switch.

5. Ignition OFF, disconnect the X2 harness connector at the BCM. Connect the harness connector at the ignition switch.
6. Ignition in ACCY, verify that a test lamp does not illuminate between ground and the run/crank voltage circuit terminal B8.

⇒ | If the test lamp illuminates, test the voltage circuit for a short to voltage.

7. Ignition OFF, disconnect the harness connector at the ignition switch. Test for less than 1.0 Ω on the run/crank circuit between BCM connector terminal B8 and ignition switch connector terminal 3.

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

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

### Component Testing

#### Ignition Switch

1. Ignition OFF, disconnect the harness connector at the ignition switch.
2. Using the Resistance Test table below, check the resistance between the terminals of the ignition switch listed in each switch position.

#### 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

⇒ | If any reading is not as specified, replace the ignition switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• | Ignition and Start Switch Replacement

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