Ignition

P031A — Misfire Detected on Engine Start-Up

Severity: medium Drive with care, to a shop

What P031A means

P031A is linked to a misfire that occurs right after the engine starts. The control module watches crankshaft speed variation and sees that one or more cylinders did not fire properly. The official SAE wording for this code can vary by manufacturer (it may be listed as reserved in generic tables), so confirm the definition for your vehicle. The closest standard code is P0316.

Symptoms

  • Check engine light on or flashing
  • Rough, shaky running right after starting
  • Hesitation or stumble when pulling away
  • Possible stalling until the engine warms up
  • Hard starting, especially when cold
  • Smell of unburned fuel from the exhaust

Possible causes

  1. Worn spark plugs
  2. Failing ignition coil
  3. Clogged or leaking fuel injector
  4. Vacuum leak or intake air leak
  5. Open circuit or poor connection in coil or injector wiring
  6. Low compression in a cylinder
  7. Crankshaft position sensor fault or signal problem

How to diagnose

  1. Read all codes and freeze frame data: engine temperature, cylinder, RPM when it set.
  2. Use a scan tool to see which cylinder has misfire counts.
  3. Inspect the spark plugs for gap, wear, deposits, cracks or oil.
  4. Swap coils between cylinders and see whether the misfire follows.
  5. Check coil and injector connectors and wiring for power and ground.
  6. Look for vacuum leaks: hoses, intake manifold gasket, or smoke test the intake.
  7. Test fuel pressure and injector operation (sound, resistance, balance).
  8. If it persists, run a compression test.

Common fixes

  • Replace spark plugs as a set
  • Replace the faulty ignition coil
  • Clean or replace the fuel injector
  • Repair vacuum leaks: hoses, gaskets
  • Repair damaged wiring or connectors

Questions and answers

What does P031A mean?

It indicates a misfire detected as the engine starts. Common causes are spark plugs, coils, injectors or a vacuum leak. Check the exact definition for your vehicle's make.

Can I drive with P031A?

Short trips are often fine if the engine runs smoothly and the light is steady. If the light flashes, stop, since the misfire can damage the catalytic converter.

How is P031A different from P0316?

P0316 is the standard code for a misfire in the first 1000 revolutions after start. P031A is similar in meaning, but its definition can vary by manufacturer.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.