GM Service Manual Online
For 1990-2009 cars only

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 B3125 00: Left Front/Driver Door Only, Unlock Circuit

DTC B3130 00: All Unlock Circuit

DTC B3135 00: All Door Lock Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

I/P Fuse Block B+

1, 2, 3

1, 2, 3

--

--

Door Latch Control

1, 2, 3

1, 2, 3

1, 2, 3

--

Doors Unlock Control

B3130 00

B3130 00

B3130 00

--

LF Door Unlock Control

B3125 00

B3125 00

B3125 00

--

Doors Locked Control

B3135 00

B3135 00

--

--

Left Lock Switch Signal

B3150 00

B3150 00

B3150 00

--

Left Unlock Switch Signal

B3140 00

B3140 00

B3140 00

--

Right Lock Switch Signal

B3155 00

B3155 00

B3155 00

--

Right Unlock Switch Signal

B3145 00

B3145 00

B3145 00

--

Door Lock Switch Ground

--

1, 2, 3

1, 2, 3

--

I/P Fuse Block Ground

--

1, 2, 3

1, 2, 3

--

1. Door Lock Malfunction

2. Driver Door Unlock Malfunction

3. Door Unlock Malfunction

Circuit/System Description

For vehicles without the RPO AXC/AXE door lock system, the body control module (BCM) controls the door lock, passenger door unlock and driver door unlock relays. Voltage is applied to the appropriate relay through the door lock/unlock control circuit when the BCM senses a door lock/unlock switch activation or a keyless entry lock or unlock command.

For vehicles with the RPO AXC/AXE door lock system, the BCM controls the rear door lock and rear door unlock relays. Voltage is applied to the appropriate relay through the door lock/unlock control circuit when the BCM receives a door lock/unlock command from either the driver door module or the passenger door module or a keyless entry lock or unlock command.

Conditions for Running the DTC

The system voltage is 9-18 volts.

Conditions for Setting the DTC

B3125 00

The BCM detects a short to ground on the LT/UNLCK relay control circuit.

B3130 00

The BCM detects a short to ground on the UNLCK relay control circuit.

B3135 00

The BCM detects a short to ground on the LCK relay control circuit.

Action Taken When the DTC Sets

The power door locks 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

Vehicle Access 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

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification

Command the driver door and passenger door lock actuators to LOCK and UNLOCK with the scan tool, the doors should perform the LOCK and UNLOCK function.

If B3125 00 is current, refer to LT/UNLCK Relay Control Circuit Malfunction.
If B3130 00 is current, refer to UNLCK Relay Control Circuit Malfunction.
If B3135 00 is current, refer to LCK Relay Control Circuit Malfunction

Circuit/System Testing

LT/UNLCK Relay Control Circuit Malfunction

  1. Ignition OFF, disconnect the LT/UNLCK relay.
  2. Connect a test lamp between the control circuit terminal 85 and the B+ circuit terminal 86.
  3. Ignition ON, command the driver door to UNLOCK with a scan tool. The test lamp should briefly illuminate when commanding the UNLOCK state.
  4. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
    If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the LT/UNLCK relay.

UNLCK Relay Control Circuit Malfunction

  1. Ignition OFF, disconnect the UNLCK relay.
  2. Connect a test lamp between the control circuit terminal 85 and the B+ circuit terminal 86.
  3. Ignition ON, command the rear doors to UNLOCK with a scan tool. The test lamp should briefly illuminate when commanding the UNLOCK state.
  4. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
    If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the UNLCK relay.

LCK Relay Control Circuit Malfunction

  1. Ignition OFF, disconnect the LCK relay.
  2. Connect a test lamp between the control circuit terminal 85 and the ground circuit terminal 86.
  3. Ignition ON, command the rear doors LOCK with a scan tool. The test lamp should briefly illuminate when commanding the LOCK state.
  4. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
    If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the LCK relay.

Component Testing

  1. Ignition OFF, disconnect the appropriate relay.
  2. Test for 60-200 ohms between terminals 85 and 86.
  3. If not within the specified range, replace the relay.
  4. Test for infinite resistance between the following terminals:
  5. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    If less than the specified value, replace the relay.
  6. Test for less than 2 ohms between terminals 30 and 87A.
  7. If greater than the specified range, replace the relay.
  8. Install a 3A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.
  9. If greater than the specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Relay Replacement
    •  Control Module References for BCM replacement, setup and programming