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 Descriptor

DTC B3808: Rear Door Lock Relay Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Driver Door Switch B+

1

1

--

--

Door Lock Relay B+

3,4

3,4

--

--

Door Unlock Relay B+

3,4

3,4

--

--

Passenger Door Switch B+

2

2

--

--

Driver Door Latch Control

1

1

1

--

Passenger Door Latch Control

2

2

2

--

Door Lock Relay Control

B3808

B3808

3,4

--

Door Unlock Relay Control

B3809

B3809

3,4

--

Liftgate Latch Control

5

5

5

--

Rear Door Latch Control

3,4

3,4

3,4

--

Door Lock Relay Ground

--

3,4

3,4

--

Door Unlock Relay Ground

--

3,4

3,4

--

1. Driver Door Latch Malfunction

2. Passenger Door Latch Malfunction

3. Rear Door Unlock Inoperative

4. Rear Door Lock Inoperative

5. Liftgate Latch Inoperative

Circuit/System Description

The body control module (BCM) internally grounds the door lock relay control circuit for the rear door lock relay when it receives a serial data message from the driver door switch (DDS) or passenger door switch (PDS). When the BCM grounds the door lock relay control circuit the rear door lock relay is energized and locks the rear doors.

Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

The BCM detects a short to ground on the door lock relay control circuit for greater than 60 seconds

Action Taken When the DTC Sets

The rear doors will not lock when using the door lock switch.

Conditions for Clearing the DTC

    • The 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

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, command the rear doors to LOCK and UNLOCK with a scan tool. The rear doors should LOCK and UNLOCK when changing between the commanded states.

Circuit/System Testing

  1. Ignition OFF, disconnect the LOCK relay.
  2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 86 and ground.
  3. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85
  5. Command the rear doors to LOCK and UNLOCK with a scan tool. The test lamp should briefly illuminate when changing between the commanded states.
  6. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
    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.
  7. If all circuits test normal, test or replace the LOCK relay.

Component Testing

Relay Test

  1. Ignition OFF, disconnect the LOCK 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 3-amp fused jumper wire between the 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 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, programming, and setup