P2C31: Ignition Coil Primary Circuit Fuse B
Do not keep driving
Stop driving if the engine warning light is flashing. A flashing light means unburnt fuel is pouring into the catalytic converter, and that destroys it in minutes — turning a modest repair into a very expensive one.
Expect the engine to be shaking badly and running on fewer cylinders than it has. A fuse feeding a group of ignition coils has blown, so those cylinders have no spark at all.
Do not just replace the fuse and carry on. It blew because something drew too much current — a failed coil, a chafed wire earthing out, or water in a connector. A new fuse without finding that will blow again, sometimes immediately.
Have the car recovered rather than driven if it is more than a short distance.
What this code means
The fuse feeding ignition coil primary circuit B has failed.
This code names a fuse, which makes it unusually specific — and unusually likely to be misread as trivial.
Ignition coils draw substantial current on their primary side, and on engines with many cylinders that load is split across more than one fused feed. The letter says which group has lost its supply, and the consequence is immediate: the cylinders on that fuse have no spark at all.
So the symptom is not subtle. Expect a serious misfire, an engine running on some of its cylinders, heavy shaking, and a flashing engine warning light. A flashing light means unburnt fuel is reaching the catalytic converter, which destroys it in minutes rather than months — this is one of the few codes where continuing to drive has an immediate and expensive cost.
A fuse is a symptom, not a cause. It blew because something drew more current than it should: a coil with a shorted primary winding, a chafed harness earthing against the engine, or water in a connector. Replacing the fuse without finding that means replacing it again, usually within minutes.
Why this page exists when its neighbours do not. Nothing in the public web documents this block — four independent searches established that on 2026-08-10. This code is written because a manufacturer named it, with its definition, in a technical service bulletin filed with the US road safety regulator, and that OEM wording agrees with the standard's own enumeration. Its neighbours have no such document, so they remain undocumented rather than guessed.
Likely causes
Start here
- Blown fuse or failed supply · easy
- Faulty ignition coil · moderate
- Chafed harness against engine or bracket · moderate
Less common
- Water ingress into connector · moderate
- Shorted actuator dragging the supply down · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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