Fuel and air

P02AA — Cylinder 5 Fuel Trim at Maximum Limit

Severity: medium Drive with care, to a shop

What P02AA means

The engine computer constantly adjusts fuel delivery to keep the air-fuel mixture correct, and on some engines it does so for each cylinder. P02AA means the correction for cylinder 5 has reached its maximum limit and can no longer make up the difference. Most often that cylinder is running lean, with too little fuel or too much air.

Symptoms

  • Check Engine light on
  • Rough idle, possible stalling
  • Loss of power and hesitation under acceleration
  • Misfire or stumbling
  • Higher fuel consumption

Possible causes

  1. Faulty or clogged fuel injector on cylinder 5
  2. Vacuum or intake air leak: hoses, intake manifold gasket
  3. Low fuel pressure from the pump, filter or regulator
  4. Failing mass airflow (MAF) or MAP sensor
  5. Faulty oxygen sensor
  6. Damaged wiring or a bad connector at the cylinder 5 injector
  7. Exhaust leak upstream of the oxygen sensor skewing readings

How to diagnose

  1. Scan all codes and freeze frame data, and note any other fuel trim or misfire codes
  2. Review short-term and long-term fuel trims at idle and under load
  3. Inspect vacuum hoses and the intake tract, and smoke test for air leaks
  4. Test fuel pressure and check that it holds after shutoff
  5. Check the cylinder 5 injector connector and wiring, and measure injector resistance and drive signal
  6. Compare cylinder performance with a balance test and inspect the cylinder 5 spark plug
  7. Check MAF, MAP and oxygen sensor readings
  8. Inspect the exhaust for leaks ahead of the sensor

Common fixes

  • Clean or replace the cylinder 5 injector
  • Repair intake leaks: replace hoses or gaskets
  • Replace a faulty MAF, MAP or oxygen sensor
  • Service the fuel system: filter, pump, pressure regulator
  • Repair the injector wiring or connector

Questions and answers

What does code P02AA mean?

The PCM could not correct fuel delivery to cylinder 5 because the trim hit its limit. This is usually a lean condition caused by an injector problem, an air leak or low fuel pressure.

Can I drive with P02AA?

Only briefly and gently, to reach a shop. Running lean for long can cause misfires and damage the catalytic converter.

Where should I start diagnosing P02AA?

Look at the fuel trim data and check the intake for air leaks. Then test fuel pressure and the cylinder 5 injector.

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.