B1555

Ignition Run/Start Circuit Failure

Body Ignition System Ignition switch/signal 🟢 Low — Fix at next service ✅ Safe to Drive
💬

What This Actually Means

In plain language — no jargon

Your vehicle's ignition system isn't properly communicating with the engine computer, like a light switch that won't send a signal to turn the light on. This prevents the engine from starting or running correctly because the ECU can't verify the ignition is in the proper position.

⚡

Symptoms You May Notice

3 known symptoms for this code
Engine won't start or cranks but doesn't turn over
Instrument cluster lights flicker or don't illuminate properly
Vehicle stalls immediately after starting
🔬

How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors the ignition switch signal voltage as it transitions through OFF, ACC, RUN, and START positions. It expects to detect proper voltage levels and state changes in sequence. If the signal is absent, incorrect, or doesn't transition properly, the fault is triggered.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Ignition RUN Signal Voltage 10.5-14.5V in RUN position <2V or >16V, or absent signal
Signal Transition Time Completes within 500ms Delayed or stuck signal state
🔧

Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Battery terminals and connections
Clean corrosion from battery posts and ensure both positive and negative terminals are tight; poor connection mimics ignition signal loss.
2
Ignition switch electrical contacts
Spray electrical cleaner into the ignition switch cylinder and cycle the key multiple times to remove internal corrosion.
3
Engine control module (ECM) connectors
Locate and reseat all ECM connectors at the module, checking for bent pins or corrosion inside the connector.
⚠️

When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1555 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.
🔄

How to Clear Code B1555

What happens after you fix the fault

Once the fault is repaired, B1555 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.