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 Descriptor

DTC B144B 02 : Run/Start Power Relay Circuit Short to Ground

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ignition Main Relay Control | B144B 02 | 1 | 2 | --
1. No Start. 2. Vehicle will start and continue to run after the ignition key is removed.

### Circuit/System Description

The body control module (BCM) controls the ignition main relay through the control circuit by applying voltage to the circuit. The ignition main relay is energized when the ignition switch is in ON or START, or when a remote start is requested.

### Conditions for Running the DTC

• | The system voltage is between 9-16 V.

• | The DTC can only run when the output is activated.

### Conditions for Setting the DTC

The BCM detects a short to ground in the ignition main relay control circuit.

### Action Taken When the DTC Sets

The module output driver will be shut down and not supply voltage to the ignition main relay control circuit.

### Conditions for Clearing the DTC

• | The current DTC will clear when the module request for the output is removed or the malfunction is no longer present.

• | A history DTC clears when the module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

### Diagnostic Aids

Short to voltage in the ignition main relay control circuit will cause the malfunction indicator lamp (MIL) to illuminate with the ignition key OFF, and the engine will remain running if started and the ignition key is removed.

### Reference Information

#### Schematic Reference

• | Body Control System Schematics

• | 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 Testing

1. Ignition OFF, disconnect the KR73 ignition main relay.
2. Connect a test lamp between the relay control circuit terminal 86 and ground.
3. Cycle the ignition ON and OFF. The test lamp should turn ON and OFF when changing S39 ignition switch positions.

⇒ | If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the K9 BCM.

4. If all circuits test normal, test or replace the KR73 ignition main relay.

### Component Testing

1. Ignition OFF, disconnect the KR73 ignition main relay.
2. Test for 70-150 Ω of resistance between terminals 85 and 86.

⇒ | If the resistance is not within the specified range, replace the KR73 ignition main relay.

3. Test for infinite resistance between the following terminals:

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

⇒ | If less than specified, replace the KR73 ignition main relay.

4. Install a 3 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground. Measure for less than 5 Ω of resistance between terminals 30 and 87.

⇒ | If greater than specified, replace the KR73 ignition main relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Refer to Control Module References for BCM replacement, setup, and programming