Engine

P03D6 — Cylinder-specific combustion fault

Severity: medium Drive with care, to a shop

What P03D6 means

The engine control module detected that combustion in one cylinder is not happening properly, usually through uneven crankshaft speed or similar signs. This is most often a misfire, but the exact wording of P03D6 can differ between manufacturers, so check the definition for your make and the freeze frame data. A cylinder needs three things to burn cleanly: spark, fuel and adequate compression.

Symptoms

  • Check engine light on or flashing
  • Rough idle or engine shaking
  • Loss of power or hesitation when accelerating
  • Worse fuel economy
  • Fuel smell from the exhaust or higher emissions
  • Hard starting

Possible causes

  1. Worn spark plug in the affected cylinder
  2. Failing ignition coil or coil wiring
  3. Clogged or failing fuel injector
  4. Vacuum leak or incorrect air-fuel mixture
  5. Low compression from valves, piston rings or head gasket
  6. Open, corroded or shorted wiring or connector at that cylinder
  7. Crankshaft position sensor or other sensor giving false data

How to diagnose

  1. Read all codes and freeze frame data, and look for related codes such as P0300-P0312.
  2. Look up the P03D6 definition for your specific make and model.
  3. Identify the affected cylinder using misfire counters on a scan tool.
  4. Inspect the spark plug and coil, then swap the coil with a neighbor and see if the fault follows.
  5. Check the coil and injector connectors and wiring for corrosion or damage.
  6. Test the injector by listening, measuring resistance or running a balance test.
  7. Check fuel pressure and look for vacuum leaks.
  8. Run a compression or leak-down test if spark and fuel check out.

Common fixes

  • Replace the spark plugs as a set
  • Replace the faulty ignition coil
  • Clean or replace the fuel injector
  • Repair wiring and connectors
  • Fix the underlying mechanical problem (valves, rings, head gasket)

Questions and answers

What does P03D6 mean?

It relates to a combustion problem in a specific cylinder, most often a misfire. The exact definition can vary by manufacturer, so it is worth checking for your vehicle.

Can I drive with P03D6?

Only briefly and under light load. If the check engine light flashes, shut the engine off, or you risk damaging the catalytic converter.

What should I check first?

Start with the spark plug and coil on the affected cylinder, since they are the most common and cheapest causes. If they are fine, move on to the injector and a compression test.

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.