B1571 — Door Ajar LR Circuit Failure

How do I diagnose B1571 myself?

Start with a scan: confirm B1571, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the door ajar LR circuit, and verify the suspect component against live data before buying parts.

What is the most common cause of B1571?

The most common causes are: body control module (BCM) fault, faulty switch, motor or actuator of the affected system, blown fuse or failed relay.

How much does it cost to fix B1571?

Repair wiring or connectors — $80–$250; BCM repair or replacement — $300–$900; Replace the switch or actuator — $120–$450. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What are the symptoms of B1571?

Drivers most often notice: warning light on the dashboard, no impact on engine operation in most cases, the affected function (locks, windows, lighting, wipers) works intermittently or not at all.

Is it safe to drive with B1571?

Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

Modern vehicles rely on a network of sensors and control modules to keep track of body functions like door status, interior lighting, locks, and security features. The body control module constantly compares incoming signals from switches and actuators against programmed thresholds. When the left-rear door ajar circuit delivers a reading that falls outside acceptable parameters — either because a signal is missing, shorted, or stuck in an unexpected state — the BCM logs B1571 and illuminates a warning light. The module typically requires the fault to appear on two consecutive ignition cycles before permanently setting the code, which filters out fleeting electrical glitches.

What makes B1571 tricky is that the left-rear door switch serves multiple purposes. It tells the BCM whether the door is open or closed, which controls the dome light, auto-lock behavior, and the security system. When this circuit fails, the module cannot reliably determine the door's status, leading to confusing behavior like a dome light that refuses to turn off or a car that won't lock properly. Along with storing B1571, the control module captures a freeze frame — a snapshot of engine RPM, vehicle speed, coolant temperature, and load at the exact moment the fault occurred. Reviewing this data before starting repairs pinpoints the conditions that triggered the failure and helps you reproduce the problem during testing.

Symptoms of B1571

• The door-open warning light stays illuminated on the instrument cluster even when all doors are securely closed
• The dome light fails to turn off or won't illuminate when a door is opened
• The central locking system behaves erratically, locks randomly, or refuses to lock at all
• The security or alarm system triggers without an obvious cause
• Interior lighting behaves unpredictably — lights may stay on or flicker
• Battery drain becomes noticeable if the faulty circuit holds a component in an active state

Common Causes of B1571

• The left-rear door ajar switch or latch mechanism has failed
• Wiring insulation chafed or broke at the door hinge or door jamb flex point
• Water intrusion corroded the door connector terminals, causing high resistance
• The body control module itself has developed an internal fault
• A related fuse blew or a relay dropped out, cutting power to the circuit
• The door latch actuator that releases the pawl has seized or malfunctioned

How to Diagnose B1571

1. Hook up an OBD2 scanner, confirm B1571 is stored, and record the freeze frame data showing engine conditions when the failure occurred.
2. Review any additional codes — related body or network codes often point to the root cause rather than the circuit that set B1571. Check manufacturer TSBs for your specific make and model; many B-series faults have documented factory fixes or software calibrations available through the manufacturer website or NHTSA database.
3. Perform a visual inspection of the wiring harness running to the left-rear door, paying close attention to the hinge area and door jamb where wires flex repeatedly and fail first.
4. Monitor live data from the door ajar switch while physically opening and closing the left-rear door — the PID should toggle between open and closed states.
5. Inspect and test the door connector for corrosion, bent pins, or loose fits that could interrupt the signal.
6. Clear the code, complete a drive cycle that recreates the freeze-frame conditions, and verify that B1571 does not return before declaring the repair complete.

Repair Options and Costs

• Repair damaged wiring or connector terminals: $80–$250
• Body control module repair or replacement: $300–$900
• Replace the door ajar switch or actuator: $120–$450

Typical part and labor costs at an independent shop break down as follows: wiring harness repair or connector remediation runs $80–$250 depending on accessibility and extent of damage; a new or refurbished BCM including programming and calibration costs $500–$900; and a left-rear door ajar switch or latch actuator replacement typically falls between $120 and $450 depending on the vehicle. In most cases where B1571 appears, the fault traces back to the door switch or a broken wire at the flex point rather than the expensive control module.

Overall, addressing B1571 ranges from roughly $80 on the low end for a simple wiring fix to $900 if the body control module requires replacement. An accurate diagnosis before purchasing parts pays for itself — the BCM is rarely the culprit, yet it tempts DIYers and shops alike into overspending.

Driving Safety Verdict

In most vehicles, B1571 does not impair engine performance, braking, or steering, making short-distance driving generally safe. However, if the fault disrupts the auto-lock function, the vehicle could remain unsecured. Inoperative exterior lighting or intermittent wipers linked to the same circuit create additional safety concerns, especially at night or in poor weather. Address the underlying cause promptly even if the car technically runs fine.

Related OBD2 codes

• B1500: Lamp Turn Signal Left Circuit Open
• B1501: Lamp Turn Signal Left Circuit Short To Battery
• B1502: Lamp Turn Signal Left Circuit Short To Ground
• B1503: Lamp Turn Signal Right Circuit Failure
• B1504: Lamp Turn Signal Right Circuit Open
• B1505: Lamp Turn Signal Right Circuit Short To Battery