OBD Code B1572: Door Ajar LR Circuit Open

Q: What does OBD code B1572 mean?

Door Ajar LR Circuit Open. The left rear door's position sensor circuit is broken or disconnected, so the car can't tell if the door is open or closed. It's like a light switch with a severed wire—the switch exists but can't communicate its state.

Q: What are the symptoms of fault code B1572?

Door ajar warning light stays on continuously, Locks won't engage or disengage properly, Interior lights malfunction or stay on

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What This Actually Means

In plain language — no jargon

The left rear door's position sensor circuit is broken or disconnected, so the car can't tell if the door is open or closed. It's like a light switch with a severed wire—the switch exists but can't communicate its state.

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Symptoms You May Notice

3 known symptoms for this code

Door ajar warning light stays on continuously

Locks won't engage or disengage properly

Interior lights malfunction or stay on

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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the door ajar switch circuit voltage on the left rear door. When the door closes, the switch should complete a circuit with a specific voltage signature. An open circuit means no signal returns, triggering the fault.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
Door Switch Voltage	0V (closed) or 12V (open position)	No voltage signal detected; open circuit condition
Circuit Resistance	< 5 ohms when closed	> 10,000 ohms (open circuit)

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

Door ajar switch connector

Inspect and reseat the connector on the left rear door latch; corrosion or loose pins are the most common cause.

2

Door ajar switch wiring harness

Check the wiring from door to door frame for cuts, pinches, or corrosion, especially at hinge flexure points.

3

Door ajar switch assembly

Replace the switch mechanism itself if connector and wiring are intact and voltage is confirmed open.

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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1572 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.

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How to Clear Code B1572

What happens after you fix the fault

Once the fault is repaired, B1572 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When

Fault has been diagnosed and repaired
You want to confirm the repair worked
Code appeared after a sensor was cleaned

⚠️ Do Not Clear When

Preparing for an emissions/PUC test
Root cause is still undiagnosed
Check engine light is flashing

Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.