Engine

P03AF — Cylinder 3 Pressure Too High

Severity: medium Drive with care, to a shop

What P03AF means

The engine control module monitors combustion in each cylinder, either with an in-cylinder pressure sensor on some engines or through indirect signals. P03AF sets when cylinder 3 combustion pressure exceeds the allowed limit. Possible causes include too much fuel, over-advanced ignition timing, carbon buildup, a mechanical fault or a faulty sensor.

Symptoms

  • Check Engine Light on
  • Rough idle or misfire
  • Reduced power or limp-style operation
  • Knocking or pinging under load
  • Higher fuel consumption
  • Harsh engine running, especially on diesels

Possible causes

  1. Leaking or faulty fuel injector on cylinder 3
  2. Spark plug or ignition coil problem on cylinder 3 (wrong plug, over-advanced spark)
  3. Carbon deposits in the combustion chamber raising compression and causing knock
  4. Mechanical fault: valves, head gasket or piston and rings
  5. Poor-quality or low-octane fuel
  6. Faulty cylinder pressure sensor, wiring or connector
  7. ECM fault (rare)

How to diagnose

  1. Read all codes and freeze frame data and look for related misfire, knock or injector codes
  2. Check the service information for your engine to see how this code is detected and whether it has an in-cylinder pressure sensor
  3. Inspect the cylinder 3 sensor wiring and connector for damage, corrosion and oil
  4. Pull the cylinder 3 spark plug and inspect it; swap coils between cylinders to see if the fault follows
  5. Test the injector: fuel trims, leakage, spray pattern and balance
  6. Run a compression test and a borescope inspection for carbon, hot spots or damage
  7. Check fuel quality and whether an ECM software update exists
  8. If all is fine, test the sensor and its signal with a scope

Common fixes

  • Replace or clean the faulty injector
  • Replace the spark plug and/or ignition coil on cylinder 3 with correct-spec parts
  • Remove carbon deposits from the combustion chamber
  • Repair the mechanical fault (head, valves, pistons)
  • Replace the cylinder pressure sensor or repair its wiring
  • Update ECM software, replace the ECM only as a last resort

Questions and answers

What does P03AF mean?

The ECM detected too much combustion pressure in cylinder 3. Fuel delivery, ignition, carbon buildup, a mechanical problem or a bad sensor can all cause it.

Can I drive with P03AF?

Only a short, gentle trip to a shop. Prolonged driving with high cylinder pressure can damage the piston and head gasket.

How do I find the cause of P03AF?

Start with the cylinder 3 spark plug, coil and injector, then check the sensor wiring, carbon buildup and compression. If those are fine, test the sensor and ECM.

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.