Code
B3133
HUMMER
B — Body
All Door Unlock Circuit High (BCM)
AI status
Completed
Completed
100%
Causes
- Short to battery (constant 12V) on the door unlock circuit
- Stuck or shorted unlock switch or remote receiver output
- Failed or shorted door lock/unlock actuator or motor
- Damaged wiring or pinched harness causing insulation failure
- Corroded or loose connector at door module, actuator or BCM
- Faulty BCM or internal BCM driver transistor
Symptoms
- Doors fail to unlock with switch or remote
- Doors unlocking unexpectedly or intermittently
- One or more door lock actuators inoperative
- Illumination of BCM-related warning or DTC lamp
- Stored unlock-related fault codes in BCM
What to check
- Scan BCM for B3133 and any related or pending codes; record freeze frame/data
- Visual inspection of door harnesses, connectors and actuators for damage or corrosion
- Check relevant fuses and relays for the door lock/unlock circuits
- Measure unlock circuit voltage at BCM connector and at each door actuator with key off
- Disconnect door actuators/aftermarket modules to isolate circuit and re-test
- Wiggle-test connectors and harness while monitoring for voltage changes
Signal parameters
- Expected inactive voltage: ~0 V (or low logic level) on unlock circuit
- Expected active voltage: near battery voltage (~12 V) when unlock commanded
- High fault condition: voltage present when circuit should be inactive
- Intermittent: voltage may appear or drop with harness movement or connector manipulation
Diagnostic algorithm
- Retrieve and record all BCM fault codes and freeze-frame data with a scan tool. Clear codes and attempt to re-create the failure to confirm persistence.
- Visually inspect driver and passenger door harnesses, connectors, and actuators for damage, water intrusion, corrosion, or aftermarket splices. Repair any obvious wiring damage.
- With ignition off, disconnect the unlock actuator/door module at each door. Measure voltage at the unlock circuit pin at the actuator connector and at the BCM connector. A steady high voltage with actuators disconnected indicates a short upstream (wiring/BCM).
- If voltage is present when it should be inactive, trace the wiring toward the source. Look for shorts to battery voltage—especially near door jambs, hinge areas, or where harness is routed.
- Temporarily disconnect remote alarm/aftermarket devices that interface with door lock circuits and re-test, in case an aftermarket device is feeding 12V back into the circuit.
- If harness and external components check good, perform a bench or in‑car BCM output driver test per factory procedure (or substitute with a known-good BCM) before replacing the BCM.
- After repairs, clear codes and perform functional tests of all lock/unlock inputs and outputs. Re-scan to confirm B3133 does not return.
Likely causes
- Wiring short to battery between BCM and door actuator/switch
- Failed actuator drawing or feeding voltage back into circuit
- Corroded connector at a door or BCM causing intermittent high reading
- Aftermarket alarm/remote incorrectly wired and feeding 12V into circuit
- Internal BCM output driver failure
Fault status
Status
BCM detected high voltage on All Door Unlock circuit (circuit voltage present when it should be low).
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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Repair manuals
Manual library for HUMMER
138
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