Engine

P03A5 — Cylinder 2 Pressure Too High

Severity: medium Drive with care, to a shop

What P03A5 means

The engine control module estimates the pressure in each cylinder using crankshaft speed variation, the knock sensor and, on some engines, an in-cylinder pressure sensor. P03A5 sets when cylinder 2 pressure is higher than expected. Typical causes are carbon buildup, overheating, wrong fuel mixture or ignition timing, or a mechanical fault.

Symptoms

  • Check engine light on
  • Rough running or misfire on cylinder 2
  • Loss of power or hesitation
  • Metallic knocking or pinging under load
  • Higher fuel consumption

Possible causes

  1. Carbon deposits in cylinder 2 raising effective compression
  2. Worn spark plug or faulty ignition coil on cylinder 2
  3. Overly advanced timing or knock from poor fuel
  4. Lean mixture from a vacuum leak or faulty injector on cylinder 2
  5. Mechanical problem: head gasket, valves or piston
  6. Faulty in-cylinder pressure sensor or its wiring
  7. ECM software issue (rare)

How to diagnose

  1. Scan all codes and freeze frame data, and look for related misfire or knock codes.
  2. Inspect the cylinder 2 spark plug and coil for wear, oil, deposits or overheating.
  3. Swap the coil with a neighboring cylinder and see whether the fault follows.
  4. Check the wiring and connector of the cylinder pressure sensor (if fitted) for breaks, corrosion or shorts.
  5. Review fuel trims and check for vacuum leaks and cylinder 2 injector operation.
  6. Run a compression test and inspect the cylinder with a borescope for carbon or damage.
  7. Check fuel quality and whether an ECM software update is available.

Common fixes

  • Replace spark plugs and any faulty coil
  • Clean carbon from the combustion chamber
  • Replace the injector or repair the vacuum leak
  • Repair wiring or replace the cylinder pressure sensor
  • Carry out engine repair for a mechanical fault
  • Update the ECM software

Questions and answers

What does P03A5 mean?

The ECM sees too much pressure in cylinder 2. Carbon, ignition or mixture problems are most common, and mechanical faults are less so.

Can I drive with P03A5?

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

Will a new spark plug and coil fix it?

If ignition is the cause, yes, and it is the cheapest first step. If the code returns, check for carbon buildup and test compression.

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.