Fuel and air

P02AB — Cylinder 5 Fuel Trim at Minimum Limit

Severity: medium Drive with care, to a shop

What P02AB means

The engine control module continuously adjusts fuel delivery, including per-cylinder corrections, based on oxygen sensor feedback and engine load. P02AB means the correction for cylinder 5 has reached its lowest allowed value and the mixture is still rich. The ECM cannot remove any more fuel, so it turns on the check engine light.

Symptoms

  • Check engine light on
  • Rough idle or hesitation
  • Higher fuel consumption
  • Fuel smell or black smoke from the exhaust
  • Sluggish acceleration
  • Sooty spark plug in cylinder 5
  • Possible fuel dilution of the engine oil

Possible causes

  1. Leaking or stuck-open fuel injector on cylinder 5
  2. Fuel pressure too high (regulator or return line problem)
  3. Damaged wiring or connector at the cylinder 5 injector
  4. Faulty or slow oxygen sensor
  5. MAF sensor reading too high
  6. Worn or fouled spark plug on cylinder 5 causing incomplete combustion
  7. ECM fault (rare)

How to diagnose

  1. Scan all codes and freeze frame data and look for related misfire or mixture codes
  2. Read short-term and long-term fuel trims on a warm engine
  3. Pull the cylinder 5 spark plug and compare it with the others for soot, oil or fuel wetting
  4. Inspect the injector connector and harness for corrosion, chafing or breaks
  5. Measure injector resistance and compare it with neighboring cylinders; listen for operation with a stethoscope
  6. Test fuel pressure and check that it holds after shutdown
  7. Check MAF and oxygen sensor readings for plausibility
  8. Run a cylinder balance test or bench-test the injector

Common fixes

  • Replace or professionally clean the cylinder 5 injector
  • Replace the fuel pressure regulator or fix the cause of high pressure
  • Repair the injector wiring or connector
  • Replace the cylinder 5 spark plug
  • Replace a faulty MAF or oxygen sensor
  • Clear codes and fuel adaptations after repair and road test

Questions and answers

What does P02AB mean?

The ECM has reduced fuel to cylinder 5 as far as it can, yet the mixture is still rich. The most common culprit is that cylinder's injector or excessive fuel pressure.

Can I drive with P02AB?

Only briefly and gently, for example to a shop. Prolonged driving on a rich mixture ruins plugs, thins the oil and can damage the catalytic converter.

Will clearing the code fix it?

No, the code will return until the cause is repaired. Start with the injector, spark plug and fuel pressure.

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.