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 B251A 01: All Door Unlatch Circuit Short to Battery
DTC B251A 02: All Door Unlatch Circuit Short to Ground
DTC B251A 04: All Door Unlatch Circuit Open
DTC B251B 01: Driver Door Unlatch High Control Circuit Short to Battery
DTC B251B 02: Driver Door Unlatch High Control Circuit Short to Ground
DTC B251B 04: Driver Door Unlatch High Control Circuit Open

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Driver Door Unlatch Control | B251A 02 | B251A 04 | B251A 01 | --
Passenger Door Unlatch Control | B251B 02 | B251B 04 | B251B 01 | --

### Circuit/System Description

The keyless entry control module and body control module (BCM) control the output functions of the power door latches. These output functions allow the keyless entry control module and BCM to command the power door latch motors to Unlatch.

When the keyless entry control module receives an input from one of the door handle switches, it checks the Lock/Unlock status of the door. If the status of the door is Lock, the keyless entry control module applies the ground for the appropriate unlatch circuit to the BCM and the BCM will unlock the door latch.

### Conditions for Running the DTC

The system voltage is 9-18 V.

### Conditions for Setting the DTC

#### B251A 01

The BCM detects a short to battery on the driver door unlatch control circuit.

#### B251A 02

The BCM detects a short to ground on the driver door unlatch control circuit.

#### B251A 04

The BCM detects an open circuit on the driver door unlatch control circuit.

#### B251B 01

The BCM detects a short to battery on the passenger door unlatch control circuit.

#### B251B 02

The BCM detects a short to ground on the passenger door unlatch control circuit.

#### B251B 04

The BCM detects an open circuit on the passenger door unlatch control circuit.

### Action Taken When the DTC Sets

The power door latches will be inoperative

### Conditions for Clearing the DTC

• | This DTC will be current for as long as the fault is present.

• | When the fault is no longer present, the DTC will be a history DTC.

• | A history DTC will clear after 50 ignition cycles.

### Reference Information

#### Schematic Reference

Door Lock/Indicator Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Power Door Locks Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Verification

Command the driver door and passenger door lock actuators to Unlock with the key fob, the doors should perform the Unlock function.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X1 at the K9 Body Control Module (BCM).
2. Ignition ON, test for B+ between the appropriate door unlatch control circuit and B+.

• | K9 Body Control Module (BCM) terminal 5

• | K9 Body Control Module (BCM) terminal 17

⇒ | If less than the specified range, test the circuit for an open/high resistance. If the circuit tests normal, replace the K77 Remote Control Door Lock Receiver (RCDLR).

3. Ignition ON, test for less than 1 V between the appropriate door unlatch control circuit and ground.

• | K9 Body Control Module (BCM) terminal 5

• | K9 Body Control Module (BCM) terminal 17

⇒ | If greater than the specified range, test the circuit for a short to voltage. If the circuit tests normal, replace the K77 Remote Control Door Lock Receiver (RCDLR).

⇒ | If less than the specified range, test the circuit for an open/high resistance. If the circuit tests normal, replace the K77 Remote Control Door Lock Receiver (RCDLR).

4. If all circuits test normal, test or replace the K9 Body Control Module (BCM).

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM or keyless entry control module replacement, setup and programming