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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
B+ (Ignition Switch) | 1, 5 | 1 | -- | --
Accessory Voltage | 1, 5 | 1 | 1 | --
Ignition 1 Voltage | 1, 5 | 1 | 1 | --
5-V Reference | 1, 5 | 1 | 1 | --
Ignition Key Resistor Signal | 1 | 1 | 1 | --
Accessory Wakeup Serial Data | U1814, 4 | U0100-U0299, P0513 00 | -- | --
Run/Crank Ignition 1 Voltage | B1428, 4 | 2 | 3 | --

1. Power Mode Mismatch--Different specific symptoms may occur depending on the vehicle operating conditions when the fault occurred.
2. Vehicle will not start and will set DTC B1370 06 in SIR.
3. The engine will continue to run after ignition key is removed.
4. This circuit is a pass through circuit in the BCM and will cause B+ fuse to open.
5. This circuit/condition will cause B+ fuse to open, and may cause a no start condition

### Circuit/System Description

This vehicles 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 operators desired power mode and activate specific discrete signals, and serial data messages for the operation of many 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 see from its own connections.

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

### Diagnostic Aids

• | A short to ground in the accessory wakeup serial data circuit will cause an open fuse to the ignition switch. DTC U1814 should be current.

• | A short to ground in the run/crank ignition 1 voltage circuit of the run crank relay will cause an open fuse to the ignition switch. DTC B1428 should be current.

• | 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 will determine if there is a power mode fault.

### Reference Information

#### Schematic Reference

• | Power Distribution Schematics

• | Body Control System 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

1. Verify that the following DTCs are not set: U1814, B1428.

⇒ | If either of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. With a scan tool, access Body Control Module, 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 (circuits) in correspondence to the ignition switch position.

#### PMM Power Mode Parameters

Ignition Switch Position | Current Power Mode | Ignition Off/Run/Crank (Off/Run Crank Voltage Circuit) | Ignition Accessory/Run (Accessory Voltage Circuit) | Ignition Run/Crank (Ignition 1 Voltage Circuit)
--- | --- | --- | --- | ---
Off Key Out | Off | Key Out/ACC | Inactive | Inactive
Off Key IN | Off | Key In/Off | Inactive | Inactive
Accessory | Accessory | Key Out/ACC | Active | Inactive
Run | Run | Run | Active | Active
Start | Crank Request | Crank | Inactive | Active

### Circuit/System Testing

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

1. Inspect for an open B+ fuse. 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

• | Off/Run/Crank voltage

• | Ignition 1 voltage

• | Accessory wakeup serial data (BCM output)

• | Run/crank ignition 1 voltage (BCM output)

2. Disconnect the harness connector at the ignition switch.
3. Verify that a test lamp illuminates between the B+ circuit terminal 3 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 performed 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 X1 harness connector at the BCM, test for less than 1.0 V between the following circuit terminals of the BCM and ground.

• | Ignition key resistor signal terminal 2

• | 5-V reference terminal 4

• | Accessory voltage terminal 21

• | Ignition 1 voltage terminal 14

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

6. Test for less than 1.0 Ω of resistance between the BCM and the ignition switch on the following circuit terminals.

• | Ignition key resistor signal, BCM terminal 4 and ignition switch terminal 4

• | Off/Run/Crank voltage, BCM terminal 2 and ignition switch terminal 5

• | Accessory voltage, BCM terminal 21 and ignition switch terminal 2

• | Ignition 1 voltage, BCM terminal 14 and ignition switch terminal 1

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

7. Test for infinite resistance between the ignition key resistor signal circuit terminal 4 of the BCM and ground.

⇒ | If less than the specified value, test the signal circuit for a short to ground.

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 3 and 1 | Terminals 3 and 2 | Terminals 3 and 5 | Terminals 3 and 4 | Terminals 5 and 4
--- | --- | --- | --- | --- | ---
Off Key Out | Infinite | Infinite | Infinite | Infinite | Infinite
Off Key IN | Infinite | Infinite | < 5.0 Ω | Infinite | Infinite
Accessory | Infinite | < 5.0 Ω | Infinite | Infinite | Infinite
Run | < 5.0 Ω | < 5.0 Ω | Infinite | Infinite | < 5.0 Ω
Start | < 5.0 Ω | Infinite | Infinite | Infinite | 1275-1325 Ω

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

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

• | Ignition and Start Switch Replacement