Fuel and air

P02A6 — Cylinder 4 Fuel Trim at Maximum Limit

Severity: medium Drive with care, to a shop

What P02A6 means

The engine control unit constantly adjusts injector pulse width to keep the air-fuel mixture in each cylinder close to target. P02A6 sets when the correction for cylinder 4 has reached its maximum limit and the PCM can no longer compensate. The cylinder is usually getting too little or too much fuel, or extra air.

Symptoms

  • Check Engine light on
  • Rough idle
  • Misfire on cylinder 4
  • Reduced power and sluggish acceleration
  • Worse fuel economy
  • Hard or delayed starting

Possible causes

  1. Clogged or faulty cylinder 4 fuel injector
  2. Intake air leak near cylinder 4: manifold gasket, hoses, vacuum lines
  3. Inaccurate oxygen, MAF or MAP sensor readings
  4. Low fuel pressure: weak pump, clogged filter, failing regulator
  5. Wiring or connector fault at the injector
  6. Spark plug or coil problem, or an engine mechanical issue (less likely)

How to diagnose

  1. Scan for all codes and review freeze frame data, noting any misfire or mixture codes
  2. Read short-term and long-term fuel trims at idle and around 2,500 rpm
  3. Inspect the intake tract, vacuum hoses and manifold gasket for leaks; smoke test if needed
  4. Test fuel pressure against the manufacturer's specification
  5. Inspect the cylinder 4 injector connector and wiring, and measure injector resistance
  6. Listen to the injectors and compare cylinder balance; swap the injector with a neighbor to see if the problem follows it
  7. Check the cylinder 4 spark plug and coil, and run a compression test if suspicious
  8. Evaluate oxygen sensor and MAF/MAP readings

Common fixes

  • Clean or replace the cylinder 4 injector
  • Fix intake leaks: replace the manifold gasket, hoses or vacuum lines
  • Replace a faulty oxygen, MAF or MAP sensor
  • Replace the fuel filter, pump or pressure regulator
  • Repair the injector wiring or connector

Questions and answers

What does P02A6 mean?

The PCM can't correct the air-fuel mixture in cylinder 4 because its fuel trim has hit the limit. The usual culprits are the injector, an air leak or low fuel pressure.

Can I drive with P02A6?

Briefly and gently, to reach a shop. If the engine misfires badly or the check engine light flashes, stop driving, since the catalytic converter can be damaged.

What should I check first?

Read the fuel trims with a scan tool and look for intake air leaks. Then test the cylinder 4 injector and the 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.