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 B1370 01: Device Ignition 1 (ON and START) Circuit Short to Battery
DTC B1370 06: Device Ignition 1 (ON and START) Circuit Short to Ground or Open
DTC B1380 01: Device Ignition ACCESSORY Circuit Short to Battery
DTC B1380 06: Device Ignition ACCESSORY Circuit Short to Ground or Open
DTC B1440 00: Power Mode Master Input Circuits Mismatch
DTC B1441 01: Device Ignition OFF, RUN, and CRANK Circuit Short to Battery
DTC B1441 06: Device Ignition OFF, RUN, and CRANK Circuit Short to Ground or Open

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
B+ - Terminal 2 | B1370 06, B1380 06, B1440 00, U0100-U0299, 1, 2 | B1370 06, B1380 06, B1440 00, U0100-U0299 | -- | --
Ignition - Terminal 1 | B1370 06, B1380 06, U0100-U0299, 1, 2 | B1370 06 | B1370 01, U0100-U0299, 1 | --
Ignition - Terminal 3 | B1370 06, B1380 06, U0100-U0299, 1, 2 | B1380 06 | B1380 01 | --
Ignition - Terminal 4 | B1370 06, B1380 06, B1440 00, U0100-U0299, 1, 2 | B1440 00, B1441 06 | B1440 00, B1441 06 | --
Ignition - BCM terminal 21, X4 | B1428, 1 | B1370 06 | -- | --
Accessory Wakeup Serial Data, BCM terminal 19, X4 | U1814, 3 | U0100-U0299, P0513 00 | -- | --

1. This circuit/condition will cause B+ fuse to open, and may cause a no start condition.
2. Scan Tool Does Not Communicate with High Speed GMLAN Device
3. This circuit is a pass through circuit in the BCM and will cause B+ fuse to open.

### 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

#### B1370 01

Ignition switch is in the OFF or ACC positions.

#### B1370 06, B1380 01, B1441 01, and B1441 06

Ignition switch is in the START position.

#### B1380 06 and B1440 00

Ignition switch is in the RUN position.

### Conditions for Setting the DTC

#### B1370 01, B1380 01, B1441 01

The circuit is shorted to voltage.

#### B1370 06

• | Ignition circuit is open.

• | Ignition, accessory, or off/run/crank circuit shorted to ground.

• | B+ circuit of the ignition switch open or shorted to ground.

• | Run crank relay coil control circuit open, including relay coil and ground.

#### B1380 06

• | Accessory circuit is open.

• | Ignition, accessory, or off/run/crank circuit is shorted to ground.

• | B+ circuit of the ignition switch open or shorted to ground.

#### B1440 00

• | BCM senses an open or short to voltage on the off/run/crank circuit when both ignition accessory/run and ignition run/crank parameters are active.

• | BCM senses an open on the B+ circuit (to the ignition switch) while engine is running. An open on the B+ circuit can be caused by a short to ground on any of the following circuits:

- | B+

- | Accessory

- | Run/crank

- | Off/run/crank

#### B1441 06

Off/run/crank circuit is open.

### Conditions for Clearing the DTC

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

### Diagnostic Aids

• | A short to ground in the ignition circuit of the run crank relay will cause the B+ circuit fuse to the ignition switch to open. 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 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

1. Verify that DTC U1814 or B1428 is not set.

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

2. 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 | Current Power Mode | Ign. Off/Run/Crank (Terminal 4) | Ignition Accessory/Run (Terminal 3) | Ignition Run/Crank (Terminal 1)
--- | --- | --- | --- | ---
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. 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 circuits listed below for a short to ground. If all circuits test OK, replace the BCM.

• | B+ terminal 2

• | Ignition terminal 3

• | Ignition terminal 4

• | Ignition terminal 1

• | Ignition terminal, BCM terminal 19, X4

• | Ignition terminal, BCM terminal 21, X4

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.

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.

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

5. Disconnect the X1 harness connector at the BCM, test for less than 1.0 volt between the following circuit terminals of the BCM and ground.

• | Ignition terminal 4

• | Ignition terminal 2

• | Ignition terminal 21

• | Ignition terminal 14

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

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

• | Ignition terminal 4, X1 and ignition switch terminal 6

• | Ignition terminal 2, X1 and ignition switch terminal 4

• | Ignition terminal 21, X1 and ignition switch terminal 3

• | Ignition terminal 14, X1 and ignition switch terminal 1

⇒ | If greater than specified, repair 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 6 | Terminals 4 and 6
--- | --- | --- | --- | --- | ---
Off Key Out | Infinite | Infinite | Infinite | Infinite | Infinite
Off Key IN | Infinite | Infinite | < 5.0 ohms | Infinite | Infinite
Accessory | Infinite | < 5.0 ohms | Infinite | Infinite | Infinite
Run | < 5.0 ohms | < 5.0 ohms | Infinite | Infinite | < 5.0 ohms
Start | < 5.0 ohms | Infinite | Infinite | Infinite | 1275-1325 ohms

### 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