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 B1440: Power Mode Master Input Circuits Mismatch

### Circuit/System Description

The body control module (BCM) monitors the ignition inputs ignition off/run/crank voltage, ignition 1 voltage and the accessory voltage signals supplied from the ignition switch. The ignition key resistor signal circuit provides 5-volt reference from the BCM to the ignition switch. The BCM uses the sequence that the signals appear, their voltage levels, the engine run flag (ERF) status and the remote start status to determine the power mode.

### Conditions for Running the DTC

Ignition switch is in the RUN position.

### Conditions for Setting the DTC

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

• | BCM senses an open on the battery positive voltage circuit while engine is running. An open on the battery voltage circuit can be caused by a short to ground on any of the following circuits :

• | Battery positive voltage

• | Accessory voltage

• | Ignition 1 voltage

• | Off/run/crank voltage

### Action Taken When the DTC Sets

• | The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the GMLAN serial data communications circuits.

• | The other modules on the vehicle operate in a fail-safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the GMLAN serial data communications circuits.

• | The vehicle may not start.

### 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 of 50, without a repeat of the malfunction.

### Diagnostic Aids

Use the DMM MIN/MAX function to capture/locate intermittent conditions.

### Reference Information

#### Schematic Reference

Power Distribution Schematics

#### Connector End View Reference

Power and Grounding Component Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Testing

1. With the ignition OFF, disconnect the BCM connector.
2. With the ignition OFF w/key out and in the ACC positions, measure for 0 volts between the off/run/crank voltage circuit at the BCM connector and ground. If over 0 volts, disconnect the ignition switch and check the off/run/crank voltage circuit for short to voltage or short to other ignition switch signal circuit.
3. With the ignition OFF w/key in, measure for battery voltage between the off/run/crank voltage circuit at the BCM connector and ground. If less than battery voltage, disconnect the ignition switch and check the off/run/crank voltage circuit for an open or short to ground.
4. With the ignition in the RUN and START positions, measure for battery voltage between the ignition 1 voltage circuit at the BCM connector and ground. If less than battery voltage, disconnect the ignition switch and check the ignition 1 voltage and battery positive voltage circuits for an open or short to ground.
5. With the ignition in the ACC and RUN positions, measure for battery voltage between the accessory voltage circuit at the BCM connector and ground. If less than battery voltage, disconnect the ignition switch and check the ignition voltage and battery positive voltage circuits for an open or short to ground.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.