GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 Envoy - 2WD 🢒 Body Systems 🢒 Vehicle Access 🢒 Power Door Locks Inoperative - Rear

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.

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 rear door lock actuators are controlled by the body control module (BCM) through the LOCK and UNLOCK relays, and the relays are controlled by the BCM through low side drive control circuits.

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 Door Lock/Unlock with a scan tool. The rear doors should preform the LOCK and UNLOCK functions.

Circuit/System Testing
  1. Ignition OFF, disconnect the UNLOCK relay.
  2. Test for less than 20 ohms between the ground circuit terminal 87A and ground.
    3. ⇒If greater than the specified range, test the ground circuit for a short to voltage or an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal listed below and ground:
    4. • B+ circuit terminal 86
    • B+ circuit terminal 87
    ⇒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 doors to UNLOCK with a scan tool. The test lamp should briefly illuminate during the UNLOCK command.
    6. ⇒If the test lamp does not illuminate, 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 continuously illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
  6. Ignition OFF, connect the UNLOCK relay and disconnect the LOCK relay.
  7. Test for less than 20 ohms between the ground circuit terminal 87 and ground.
    8. ⇒If greater than the specified range, test the ground circuit for a short to voltage or an open/high resistance.
  8. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
  9. Command the doors to LOCK with a scan tool. The test lamp should briefly illuminate during the LOCK command.
    10. ⇒If the test lamp does not illuminate, 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 continuously illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
  10. Ignition OFF, connect the LOCK relay and disconnect the harness connector at the appropriate rear door latch.
  11. Test for less than 20 ohms between the control circuit terminal A and ground.
    12. ⇒If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, test or replace the UNLOCK relay.
  12. Test for less than 20 ohms between the control circuit terminal B and ground.
    13. ⇒If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, test or replace the LOCK relay.
  13. Connect a test lamp between the control circuit terminal A and ground.
  14. Command the doors to UNLOCK with a scan tool. The test lamp should briefly illuminate during the UNLOCK command.
    15. ⇒If the test lamp does not illuminate, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, test or replace the UNLOCK relay.
    ⇒If the test lamp continuously illuminates, test the control circuit for a short to voltage. If the circuit tests normal, test or replace the UNLOCK relay.
  15. Connect a test lamp between the control circuit terminal B and ground.
  16. Command the doors to LOCK with a scan tool. The test lamp should briefly illuminate during the LOCK command.
    17. ⇒If the test lamp does not illuminate, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, test or replace the LOCK relay.
    ⇒If the test lamp continuously illuminates, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, test or replace the LOCK relay.
  17. If all circuits test normal, test or replace the rear door latch.

Component Testing

Relay Test

  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.
  3. Test for infinite resistance between the following terminals:
    4. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    ⇒If less than the specified value, replace the relay.
  4. Test for less than 2 ohms between terminals 30 and 87A.
    5. ⇒If greater than the specified range, replace the relay.
  5. 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.
    6. ⇒If greater than specified range, replace the relay.

Door Latch Assembly Test

  1. Ignition OFF, disconnect the harness connector at the appropriate door latch.
  2. Install a 15 amp fused jumper wire between the control terminal A and 12 volts. Momentarily install a jumper wire between the control terminal B and ground. The door latch should perform the LOCK/ UNLOCK function.
    3. ⇒If the function does not perform as specified, replace the door latch.
  3. Reverse the jumper wires; the door latch assembly should perform the UNLOCK/LOCK function.
    4. ⇒If the function does not perform as specified, replace the door latch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Relay Replacement
    •  Rear Side Door Latch Replacement
    •  Control Module References for BCM replacement, setup, and programming