Code
B29C1
MITSUBISHI
B — Body
Door unlock signal:short to BAT
Views:
UK: 13
EN: 11
RU: 12
AI status
Completed
Completed
100%
Causes
- Short to battery (B+) in door unlock signal wire
- Faulty door unlock switch or remote unlock input stuck ON
- Failed door lock actuator drawing backfeed voltage
- Damaged wiring harness or chafed insulation near door hinge/door jamb
- Poor or corroded connector pin making intermittent contact
- Aftermarket alarm/remote or electric accessory wired incorrectly
Symptoms
- Doors unlock intermittently or unlock on their own
- Unable to operate door unlock normally from switch or remote
- Fuse for door circuits may blow or show signs of stress
- Battery drain if circuit is stuck on
- Stored B29C1 fault and possibly other body-control faults
What to check
- Verify current stored DTCs and freeze frame with an OBD/diagnostic scanner
- Visually inspect wiring and connectors at affected door, hinge boots and BCM for damage or corrosion
- Check for aftermarket alarms or remote start modules that tie into unlock circuit
- Inspect relevant fuses and fusible links for damage
- Backprobe the unlock signal pin at BCM/door module and monitor voltage with door unlocked and locked
- Disconnect door module/actuator and see if code clears or behavior changes
Signal parameters
- Unlock signal inactive: ~0 V (pulled low or open circuit)
- Unlock signal active: ~12 V pulse to battery voltage (approx. 11–14 V) when unlock commanded
- If shorted to B+: constant ~11–14 V present with no unlock request
- Expected continuity to battery when actively driven by unlock (only during command)
Diagnostic algorithm
- Read and record freeze frame and all related codes with a scan tool. Clear codes and attempt to re-run to confirm repeatability.
- Inspect the vehicle for aftermarket modules tied to door unlock wiring; disconnect them temporarily if present.
- Visually inspect fuse box, BCM, door harness, door jamb boot and connectors for damage, corrosion or moisture. Repair visible wiring damage.
- With ignition OFF, backprobe the unlock signal wire at the BCM and measure voltage. It should be ~0 V when no unlock request is active. If ~12 V present, suspect short to B+ or a stuck switch/module.
- Operate unlock from each source (driver switch, passenger switch, remote) and note which commands change the signal. If none change it, fault likely upstream (short or BCM).
- Disconnect the door lock actuator/switch or harness at the door and re-check the unlock signal at the BCM. If voltage returns to normal, suspect short/shorted actuator or switch in the door.
- If the short follows to the harness in the door, remove inner door trim and inspect/repair the wiring around the hinge/joint and connectors. Repair or replace damaged wiring or connectors.
- If harness and door components check good, test/replace suspect door control module or BCM only after confirming wiring and external modules are isolated.
- After repair, clear codes and perform functional tests and a road/profile test to confirm the fault does not return. Observe battery voltage during testing to ensure no parasitic draw.
- Safety note: disconnect the battery before performing major connector/wiring repairs and avoid shorting battery terminals.
Likely causes
- Shorted unlock signal wire to battery at door harness or connector
- Failed/unseated door unlock switch or actuator causing continuous feed
- Aftermarket alarm/remote module backfeeding the unlock circuit
- Corroded connector or pin causing unintended B+ connection
Fault status
Status
Door unlock signal circuit detected short to battery voltage (B+). Investigate wiring, connectors, door switch/actuator and any aftermarket modules for a short or backfeed.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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