Diagnostic Instructions
Perform the Diagnostic System Check - Door Systems prior to using this diagnostic procedure.
DTC Descriptor
DTC B3127: LF Door Only Unlock Circuit LowDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
BCM B+ | 1 | 1 | -- | -- |
Driver Door Lock Switch Signal | B3272 | 1 | 1 | -- |
Passenger Door Lock Switch Signal | B3272 | 1 | 1 | -- |
Driver Door Lock Control | B3127, B3137 | B3128, B3138 | 1 | -- |
Passenger Door Lock Control | B3132, B3137 | B3133, B3138 | 1 | -- |
Rear Door Lock Control | B3132, B3137 | B3133, B3138 | 1 | -- |
Driver Door Lock Switch Ground | -- | 1 | 1 | -- |
Passenger Door Lock Switch Ground | -- | 1 | 1 | -- |
1. Door Locks Malfunction | ||||
Circuit/System Description
The body control module (BCM), upon receipt of a lock switch lock signal, will provide and ground to the door latch unlock control circuit while simultaneously providing voltage to the door latch lock control circuit causing the door latch to perform the lock function. When the BCM receives a lock switch unlock signal, the BCM will provide and ground to the door latch lock control circuit while simultaneously providing voltage to the door latch unlock control circuit causing the door latch to perform the unlock function.
Conditions for Running the DTC
The system voltage must be between 9-16 volts.
Conditions for Setting the DTC
The BCM detects a short to ground in the driver door unlock control circuit while commanding the door latches.
Action Taken When the DTC Sets
The power door locks will malfunction.
Conditions for Clearing the DTC
| • | This DTC will change from current to history when the fault is no longer present. |
| • | A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present. |
Reference Information
Schematic Reference
Door Lock/Indicator Schematics
Connector End View Reference
Power Door Systems Connector End Views
Description and Operation
Power Door Locks Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
Ignition ON, observe the function of the driver door latch while commanding the Driver Door Unlock and Door Lock with a scan tool. The driver door should perform the LOCK and UNLOCK function.
Circuit/System Testing
- Ignition OFF, disconnect the C2 harness connector at the driver door lock.
- Connect a test lamp between the control circuit terminal A and ground.
- Ignition ON, command the Driver Door Unlock with a scan tool. The test lamp should briefly illuminate during the UNLOCK command.
- If all circuits test normal, test or replace the driver door lock.
| ⇒ | 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. |
Component Testing
- Ignition OFF, disconnect the harness connector at the driver door latch.
- Install a 20A fused jumper wire between one of the control terminals and 12V. Momentarily install a jumper wire between the other control terminal and ground. Reverse the jumper wires at least two times, the driver door latch should perform the LOCK/UNLOCK functions.
| ⇒ | If it does not perform as specified, replace the driver door latch |
Repair Instructions
| • | Body Control Module (BCM) Programming/RPO Configuration for BCM replacement, setup, and programming |
