Diagnostic Instructions
| • | Perfrom 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 B3127: LF Door Only Unlock Circuit LowDTC B3132: All Door Unlock Circuit Low
DTC B3137: All Door Lock Circuit Low
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Door Lock/Unlock Signal | 1,2,3 | 1,2,3 | 1,2,3 | -- |
Driver Door Lock Actuator Unlock Control | B3127 | 2 | 2 | -- |
Door Lock Actuator Unlock Control | B3132 | 3 | 3 | -- |
Door Lock Actuator Lock Control | B3137 | 1 | 1 | -- |
Door Lock Switch Ground | -- | 1,2,3 | 1,2,3 | -- |
1. Door Locks Inoperative 2. Driver Door Unlock Inoperative 3. Door Unlock Inoperative | ||||
Circuit/System Description
The BCM (PWR) fuse supplies battery positive voltage to the body control module (BCM) for the door lock system.
The BCM supplies and monitors a reference voltage to the door lock switch through the door lock switch lock/unlock signal circuit. The door lock switch also receives a constant ground source. If a door lock switch is placed in the lock position, the reference voltage is taken directly to ground and the BCM senses 0.0 volts on the signal circuit. If a door lock switch is placed in the unlock position, the reference voltage is taken to ground through a 1.5k ohm resistor that is internal to the door lock switches and senses approximately 2.9 volts on the signal circuit. This is how the BCM determines what portion of the door lock switch was activated.
The BCM, upon receipt of a door lock switch lock or unlock signal, will switch the appropriate door lock actuator control circuits to battery positive voltage. The opposing side of the door lock actuators are connected to ground internally within the BCM through the other door lock actuator control circuit and the doors will lock or unlock appropriately.
Vehicles without keyless entry have 2 internal drivers in the BCM to control the door lock actuators. All door lock and all door unlock. Vehicles equipped with keyless entry have three internal drivers in the BCM. Driver door unlock, passenger door unlock and all door lock. This is done to isolate the driver door lock actuator so it can be unlocked by itself using the keyless entry transmitter.
Conditions for Running the DTC
Battery voltage must be between 9-16 volts.
Conditions for Setting the DTC
B3127
The BCM does detects low voltage on the driver door lock actuator unlock control circuit.
B3132
The BCM does detects low voltage on the door lock actuator unlock control circuit.
B3137
The BCM does detects low voltage on the door lock actuator lock control circuit.
The conditions above must be present for more than 0.3 second.
Action Taken When the DTC Sets
| • | The BCM stores the DTC to memory. |
| • | The door lock actuators will not lock or unlock. |
Conditions for Clearing the DTC
| • | A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present. |
| • | The technician issues a scan tool CLEAR DTCs command. |
Diagnostic Aids
If DTC B3127, DTC B3132 and B3137 have all been set, the fault may be any of the following:
| • | The BCM has an internal open. |
| • | An open BCM (PWR) 15-amp fuse, which could be caused by any of the following: |
| - | The BCM is shorted to ground internally. |
| - | Any of the door lock actuator lock or unlock control circuits are shorted to ground. |
| • | If only a single DTC is set as current and other DTCs will not set with multiple lock and unlock switch activations, the BCM is internally open. |
Reference Information
Schematic Reference
Door Lock/Indicator Schematics
Connector End View Reference
Description and Operation
Power Door Locks Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
Ignition ON, command the Door Latch to Lock and Unlock with the scan tool, the doors should Lock and Unlock.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the appropriate Door Latch.
- Ignition OFF, test for less than 1.0 ohm of resistance between the control circuit terminal 2 and ground.
- Ignition OFF, test for less than 1.0 ohm of resistance between the control circuit terminal 3 and ground.
- Connect a test lamp between control circuit terminal 2 and control circuit terminal 3.
- Ignition ON, command the Door Latch to LOCK and UNLOCK with a scan tool. The test lamp should turn ON when commanding the LOCK and UNLOCK states.
- If all circuits test normal, test or replace the appropriate Door Latch.
| ⇒ | If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If circuits test normal, replace the BCM. |
| ⇒ | If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If circuits test normal, replace the BCM. |
| ⇒ | If the test lamp remains OFF during either of the commands and the circuit fuse is good, test for a short to ground on either control circuit. If the circuits test normal, replace the BCM. |
| ⇒ | If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the Door Latch. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup and programming |
