B3125 on GMC: How to Diagnose & Fix
Driver Door Only Unlock Circuit Malfunction
1 GMC model · 1 documented issue · $180-$500 repair
B3125 on GMC by model: symptoms, diagnosis and fix
GMT900 Sierra trucks are well known for failing door lock actuators, often starting with one door that unlocks weakly or only works intermittently before additional doors fail. Owners report the key fob cycling the locks while one or more doors remain stuck, requiring manual operation from inside. The issue is heavily documented across GM full-size truck forums and complaint records.
Common Symptoms
- door will not lock or unlock with key fob
- weak buzzing from inside door
- intermittent power lock operation
- one or more doors stuck locked
- manual lock works but power lock does not
How to Fix
Diagnosis involves confirming power and ground at the latch/actuator assembly and ruling out broken door-jamb wiring or BCM command issues. The usual fix is replacement of the failed actuator or latch-actuator assembly in the affected door, followed by checking all doors because multiple actuators often fail within a similar time period.
Sources for this issue (2)
B3125 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does B3125 mean on a GMC?
B3125 stands for "Driver Door Only Unlock Circuit Malfunction." B3125 is a body code, commonly defined on GM/Opel-family vehicles as a malfunction in the driver-door-only unlock circuit. The body control module provides voltage and ground to the door lock actuators to perform lock/unlock commands, and it sets this code when it detects a short to battery, short to ground, or open in the driver-door unlock control circuit. The most common symptom is inoperative power door locks for that function; it is a convenience fault, not a safety issue. On GMC it is documented across 1 model: Sierra 1500.
What are the most common causes of B3125?
The most common causes of B3125 are: Short to battery or ground in the driver unlock circuit, Open circuit / broken wire (often at the door boot), Failed driver door lock actuator, Corroded or damaged door harness connector, Water intrusion into the door module/connector, Body control module output driver fault. The specific cause varies by vehicle.
How much does it cost to fix B3125 on a GMC?
Published repair estimates on GMC range from $180 to $500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.