B1559

Door Lock Cylinder Circuit Failure

Body Chassis/Safety Door Lock System 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The vehicle's door lock cylinder circuit is not responding properly to the locking system—think of it like a light switch that won't communicate back to confirm whether it's on or off. The ECU expects to see electrical feedback from the lock mechanism but isn't getting the signal it needs.

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Symptoms You May Notice

3 known symptoms for this code
Door locks not functioning or responding inconsistently
Keyless entry or remote lock/unlock failures
Warning light on dashboard related to door locks or security
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors voltage and resistance in the door lock cylinder circuit to confirm the solenoid actuator is operating correctly. It expects a specific voltage pattern when the lock is commanded open or closed, and flags a fault if resistance or signal amplitude falls outside normal operating parameters or drops to zero.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Lock Circuit Voltage 10-14V during actuation <8V or >15V, or no signal
Circuit Resistance 5-50 ohms when active >200 ohms or open circuit
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Door lock wiring harness connector
Inspect and clean the connector at the door lock actuator for corrosion, moisture, or loose pins.
2
Door lock cylinder solenoid
Test solenoid continuity with a multimeter; replace if open or shorted circuit is detected.
3
Door lock control module or relay
Verify relay clicks when door lock button is pressed; replace relay if no audible response.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1559 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 B1559

What happens after you fix the fault

Once the fault is repaired, B1559 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.