Code
B3132
HUMMER
B — Body
All Door Unlock Circuit Low (BCM)
AI status
Completed
Completed
100%
Causes
- Short to ground on the All-Door Unlock wiring
- Open or shorted harness or damaged insulation (pinched, chafed)
- Corroded or loose connector terminals at BCM or door harness
- Blown fuse or faulty relay in lock/unlock feed
- Failed door lock actuator or motor creating a low/short condition
- Faulty BCM output driver
Symptoms
- Doors fail to unlock using remote or interior unlock switch
- Only some doors unlock or unlock operation is intermittent
- Repeated DTC B3132 stored in BCM
- Fuse for locks may blow or click/relay chatter when unlocking is attempted
- Possible battery drain if short is present
What to check
- Read and record freeze frame and related codes with a scan tool; note key state and command status
- Inspect fuses and relays related to door locks and BCM power
- Visual inspection of BCM connector pins and door harness connectors for corrosion, bent pins, or water damage
- Check for aftermarket alarm/remote modules and verify proper wiring
- Perform wiggle test while commanding unlock and watching scan data/actuator behavior
- Measure voltage at BCM unlock output with harness connected and while commanding unlock
Signal parameters
- Idle unlock output: near 0 V (depends on design); when commanded may be driven to battery voltage (~12–14 V) or switched to ground depending on vehicle
- When commanding unlock from a scan tool: see a clear change in the unlock output (0 V → ~12 V or vice versa) if driver is functioning
- Expected actuator current: typically up to a few amps while motor runs (varies by model) — sudden low-resistance (
- Continuity: unlock circuit should show continuity to actuator and not continuity to ground except during intended ground-switching designs; measure per factory wiring diagram
Diagnostic algorithm
- Use scan tool to verify B3132 and check for other related BCM or communication codes (U-codes). Record freeze frame data.
- Inspect fuses/relays and replace any blown items. Check for immediate re-blow when operation is attempted (indicates short).
- Visually inspect BCM and door harness connectors for corrosion, bent pins, or moisture. Repair any damaged terminals.
- With ignition on, use a scan tool to command All-Door Unlock and observe BCM output using a DVOM or oscilloscope at the BCM unlock pin. Note voltage/state changes.
- If output is held low unexpectedly, disconnect connectors downstream (door harness/actuators) and repeat the command. If the output returns to expected behavior with downstream connectors disconnected, suspect a short or failed component in the harness or actuators.
- Isolate by reconnecting one door connector at a time and testing until the fault reappears to find the affected circuit/component.
- Check continuity between unlock output and chassis ground with harness disconnected to confirm short to ground. Compare resistance readings to known-good or vehicle-specific specs.
- Inspect door jamb areas where harness flexes for chafing or water ingress; repair or replace damaged harness sections and terminals as needed.
- If wiring and actuators test good and the unlock output still behaves incorrectly, suspect a faulty BCM output driver. Verify power/ground to BCM then consider BCM replacement or repair per vehicle procedures.
- Clear codes and re-test complete system. Confirm proper unlock operation and that the code does not return.
Likely causes
- Short to ground on the unlock output circuit
- Corroded/loose connector at BCM or door harness
- Failed BCM unlock driver
- Damaged wiring in the harness (door jamb area)
- Faulty door lock actuator presenting a short when commanded
Fault status
Status
B3132 — All Door Unlock Circuit Low: BCM detects unexpected low voltage/possible short to ground on the all-door unlock output circuit. May prevent unlock commands from operating and can indicate wiring, actuator, or BCM failure.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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138
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