Ignition

P03C6 — Cylinder 6 Misfire Detected

Severity: medium Drive with care, to a shop

What P03C6 means

The engine control unit watches crankshaft speed and can tell when cylinder 6 fails to burn its air-fuel mixture properly. Each cylinder needs a spark, the right amount of fuel and enough compression to fire correctly. If any of these is missing, the cylinder misfires and the ECU stores P03C6.

Symptoms

  • Rough idle and engine shaking
  • Loss of power, hesitation or stumbling on acceleration
  • Check engine light on or flashing
  • Worse fuel economy
  • Raw fuel smell from the exhaust
  • Hard starting

Possible causes

  1. Failed ignition coil on cylinder 6
  2. Worn or fouled spark plug in cylinder 6
  3. Clogged or faulty fuel injector on cylinder 6
  4. Low compression from worn rings, valves or a head gasket leak
  5. Damaged wiring or a poor connector contact at the coil or injector
  6. Vacuum or intake air leak near cylinder 6
  7. Rarely, a failed driver circuit in the ECU

How to diagnose

  1. Scan all codes and read freeze frame data; look for other misfire or fuel trim codes.
  2. Inspect the cylinder 6 coil and injector connectors and wiring for damage, corrosion and ground problems.
  3. Pull the cylinder 6 spark plug and check the electrode wear, gap and deposits.
  4. Swap the cylinder 6 coil with a neighboring cylinder and see whether the misfire follows it.
  5. Do the same with the spark plug or injector if the coil is not at fault.
  6. Check the injector's resistance and listen for its clicking with a stethoscope.
  7. Run a compression or cylinder leak-down test.
  8. Inspect the intake and vacuum hoses for air leaks.

Common fixes

  • Replace the cylinder 6 ignition coil
  • Replace the spark plugs, preferably as a full set
  • Clean or replace the cylinder 6 fuel injector
  • Repair the wiring or connector
  • Fix the mechanical engine fault (valves, rings, head gasket)

Questions and answers

Can I drive with code P03C6?

Only briefly and under light load if the check engine light is steady. If it flashes, do not drive, since the misfire can quickly damage the catalytic converter.

What most often causes P03C6?

Usually a bad ignition coil or spark plug in cylinder 6. Swapping the coil to another cylinder is a quick way to confirm it.

Should I replace all spark plugs if only one cylinder misfires?

If the plugs are old, replacing the full set makes sense because the others are equally worn. Confirm first that the coil or injector is not the real cause.

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.