Fuel and air

P02AC — Cylinder 5 Injector Restricted Flow

Severity: medium Drive with care, to a shop

What P02AC means

The engine control module compares the actual air-fuel mixture and cylinder performance with what it expects. With P02AC, it has concluded the cylinder 5 injector is delivering less fuel than commanded, leaving that cylinder lean. A clogged injector is the usual culprit, but wiring or fuel supply problems can cause the same result.

Symptoms

  • Check Engine light on
  • Rough idle
  • Misfires or engine shaking
  • Reduced power and sluggish acceleration
  • Higher fuel consumption
  • Increased emissions or exhaust odor

Possible causes

  1. Clogged or carbon-fouled cylinder 5 injector
  2. Mechanical failure of the injector
  3. Damaged wiring or poor connector contact at the injector
  4. Low fuel pressure or a clogged fuel filter
  5. Poor-quality or contaminated fuel
  6. Intake air leak skewing the mixture
  7. Rarely, an ECM fault or software issue

How to diagnose

  1. Scan all codes and freeze frame data, and look for cylinder 5 misfire codes
  2. Review short and long term fuel trims and mixture adaptation values
  3. Compare cylinder balance or contribution tests
  4. Inspect the cylinder 5 injector connector and wiring, and check power and control signal
  5. Measure injector coil resistance and compare it with the neighboring injectors
  6. Test fuel pressure and delivery volume
  7. Check for intake air leaks and exhaust leaks
  8. Swap the injector with another cylinder to see if the fault follows it

Common fixes

  • Clean the cylinder 5 injector
  • Replace the faulty injector
  • Repair the wiring or connector
  • Replace the fuel filter and clean the fuel system
  • Fix any intake air leak

Questions and answers

What does P02AC mean?

It means the ECM sees restricted fuel delivery from the cylinder 5 injector. That cylinder gets too little fuel, so the mixture runs lean.

Can I drive with P02AC?

Only briefly and under light load, to reach a shop. Prolonged driving lean risks cylinder overheating and catalytic converter damage.

Will injector cleaner fix it?

If the cause is deposits, cleaning can help, especially a bench or ultrasonic cleaning. If the injector is worn out or the problem is wiring, you'll need a replacement or repair.

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.