B1571 — Door Ajar LR Circuit Failure #

Note: The code description may vary depending on the vehicle manufacturer. Always refer to your OEM (Original Equipment Manufacturer) documentation for exact terminology.

• B1571 — Door Ajar LR Circuit Malfunction (Ford)
• B1571 — Left Rear Door Ajar Switch Circuit Failure (General Motors/Chevrolet)
• B1571 — Rear Left Door Open Signal Error (Toyota)

Summary of DTC B1571 #

The B1571 code indicates a fault detected in the left rear (LR) door ajar circuit. This circuit monitors whether the left rear door is properly closed. If the system detects an inconsistent or implausible signal from this circuit, it triggers the B1571 code and may illuminate a warning light on the dashboard. While this issue is not typically related to engine or transmission performance, it can affect vehicle security systems and interior functions like dome lighting. An unresolved B1571 may also interfere with advanced features such as automatic locking or intrusion alarms. Addressing this fault quickly ensures your vehicle’s safety features work as intended.

Common Symptoms for DTC B1571 #

Drivers may notice several signs when the B1571 code is active. These symptoms typically relate to the vehicle’s security, lighting, or warning systems. Recognizing these clues can help speed up the diagnostic process:

• Warning light or message stating “Door Ajar” or “Left Rear Door Open”
• Interior dome/interior lights staying on or not coming on as expected
• Alarm system failing to arm/disarm correctly
• Automatic door locks not activating when driving off
• Chime or audible warning when all doors appear closed
• Battery drain if interior lights remain powered

Most Probable Causes for DTC B1571 #

The B1571 code can be triggered by several issues, but some causes are more common than others. Understanding these can help prioritize your troubleshooting:

1. Faulty door ajar switch: The switch inside the left rear door may wear out or stick.
2. Wiring issues: Damaged, pinched, or corroded wires/connectors in the LR door ajar circuit.
3. Misaligned door latch: The door latch may not fully engage, causing a false open signal.
4. Faulty Body Control Module (BCM): Rare, but the BCM (the computer managing body electronics) could misinterpret correct signals.
5. Water intrusion: Moisture inside the door can corrode contacts or short the circuit.

Step-by-Step Diagnosis for DTC B1571 #

A methodical approach will help you pinpoint the root cause of the B1571 code. Here’s how to proceed:

• 1. Verify the code: Use a professional scan tool to confirm B1571 is present and clear any other codes.
• 2. Check door operation: Open and close the left rear door several times. Observe if the dash warning changes.
• 3. Inspect the door ajar switch: Locate the LR door ajar switch (often built into the latch). Check for visible damage or sticking.
• 4. Test the circuit: With a multimeter, measure continuity between the door switch and the BCM. Look for open or short circuits.
• 5. Check wiring and connectors: Carefully inspect harnesses for broken wires, corrosion, or loose pins, especially where the harness enters the door.
• 6. Evaluate the latch alignment: Confirm the door closes snugly and the latch fully engages. Adjust as needed.
• 7. Scan BCM inputs: Use a scan tool to monitor the LR door status in real time; see if it matches actual door position.
• 8. Test with a known-good switch: If in doubt, swap the switch with another door (if compatible) to isolate the fault.

Potential Repairs for DTC B1571 #

Once the root cause is found, targeted repairs can resolve the B1571 code. Each fix should address the underlying issue, not just clear the code:

• Replace a faulty door ajar switch or latch assembly if defective.
• Repair or replace damaged wiring or corroded connectors in the LR door circuit.
• Realign or adjust the door latch if misfit is detected.
• Seal the door against water intrusion and clean contacts as needed.
• In rare cases, replace/reprogram the BCM if it is proven faulty after all other steps.

Is It Safe to Drive with B1571? #

Yes, but with limitations. While the B1571 code does not directly affect engine performance or drivability, it can compromise certain safety and security features. For example, your alarm system may not function, or interior lights might drain the battery if left on. If the issue is causing distraction, battery drain, or leaving your vehicle vulnerable, it’s wise to address it promptly. Avoid long-term driving without repair.

Vehicles Most Commonly Affected by B1571 #

The B1571 code is most frequently reported on vehicles using sophisticated door ajar monitoring circuits, especially those from the following manufacturers:

• Ford (Focus, Fusion, Escape, Explorer, F-150 series)
• Lincoln (MKZ, MKC, Navigator)
• Chevrolet (Malibu, Impala, Silverado)
• Toyota (Camry, Prius, Highlander)
• Honda (Civic, Accord, CR-V — less common but possible)

Common Mistakes & Best Practices for B1571 #

Misdiagnosis often leads to costly or unnecessary repairs. Here are some pitfalls to avoid, and tips for a smooth fix:

• Replacing the latch without checking wiring first
• Overlooking water or corrosion damage inside the door
• Assuming all door ajar issues are caused by the switch — always test wiring and latch alignment
• Neglecting to check scan tool data for real-time door status
• Best practice: Always use OEM or high-quality replacement parts for switches/latches

Express FAQ: B1571 #

Here are quick answers to common questions about B1571:

• Q: Will clearing the code fix the problem?
  A: No. The code will return unless the underlying electrical or mechanical fault is repaired.
• Q: Can cold weather trigger this code?
  A: Yes, extreme cold can cause switches or latches to stick, especially if moisture is present.
• Q: My alarm keeps going off randomly — could this be related?
  A: Absolutely. A false “door open” signal can trigger security system false alarms.