• 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.

The body control module (BCM) controls the ignition main relay through the control circuit by applying voltage to the circuit. The power supply transformer samples the system voltage on the Ignition 1 voltage circuit from the ignition main relay. If the power supply transformer detects a fault in the circuit it will request the ECM to set the DTC and illuminate the MIL.

The control module ignition voltage signal is valid, with the ignition OFF.

The control module ignition voltage signal is valid, with the ignition ON.

The control module detects greater than 6 V or greater on the ignition voltage circuit, with the ignition turned OFF.

The control module detects 6 V or less on the ignition voltage circuit, with the ignition turned ON.

DTCs P305B and P305C are Type B DTCs.

DTCs P305B and P305C are Type B DTCs.

A short to voltage in the ignition circuit will keep the vehicle modules awake, which can drain the vehicle’s battery.

Power Distribution Schematics

Starting and Charging Schematics

Master Electrical Component List

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Power Mode Description and Operation

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Control Module References for scan tool information

1. Engine running.
2. Verify DTC B144B is not set.
• If the DTC is set

  Refer to DTC B144B.

• If the DTC is not set
3. Refer to Circuit/System Testing.

1. Ignition OFF, and all vehicle systems OFF, disconnect the X1 harness connector at the T19 Power Supply Transformer.
2. Test for less than 1 V between the ignition circuit terminal 6 and ground.
• If 1 V or greater

  Repair the short to voltage on the circuit.

• If less than 1 V
3. Ignition ON.
4. Verify a test lamp illuminates between the ignition circuit terminal 6 and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF remove the test lamp.
2. Test for less than 2 Ω in the ignition circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, refer to Power Mode Mismatch.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF remove the test lamp
2. Test for infinite resistance between the ignition circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If the test lamp illuminates
5. Replace the T19 Power Supply Transformer.

Perform the Diagnostic Repair Verification after completing the repair.

Refer to Control Module References for control module replacement, programming, and setup.