Fuel and air

P02F9 — Cylinder 12 Injector Circuit Range/Performance

Severity: medium Drive with care, to a shop

What P02F9 means

The engine control module fires each fuel injector by switching its circuit to ground for a precise time, and it monitors the current and voltage in that circuit. P02F9 is stored when the cylinder 12 injector signals fall outside the expected range or the injector does not perform as commanded. It applies only to engines with at least 12 cylinders, and cylinder numbering varies by manufacturer.

Symptoms

  • Check Engine Light on
  • Rough idle
  • Misfire, hesitation or stumbling under acceleration
  • Reduced engine power
  • Higher fuel consumption
  • Increased exhaust emissions

Possible causes

  1. Faulty cylinder 12 injector (bad coil, clogged or stuck)
  2. Damaged or corroded wiring or connector in the injector circuit
  3. Poor electrical connection or weak ground
  4. Intake air leak upsetting the mixture
  5. Fuel supply problem such as low pressure, weak pump or clogged filter
  6. Failed injector driver in the PCM (rare)

How to diagnose

  1. Scan all codes and freeze-frame data, and look for other injector or misfire codes.
  2. Inspect the cylinder 12 injector connector and harness for corrosion, chafing or burned terminals.
  3. Review fuel trims and cylinder balance data and compare cylinder 12 with the others.
  4. Measure the injector coil resistance and compare it with the manufacturer spec.
  5. Check for power and the control pulse at the connector with a scope or noid light.
  6. Test the wire between injector and PCM for opens, shorts and excess resistance.
  7. Measure fuel pressure and inspect the intake for vacuum leaks.
  8. Swap the injector with a neighbor and see whether the fault follows it.

Common fixes

  • Replace the cylinder 12 injector, or have it professionally cleaned if it is only dirty
  • Repair the wiring or replace the damaged connector or terminals
  • Clean and secure the connections and restore the ground
  • Fix the air leak or fuel supply fault
  • Replace or reprogram the PCM only after everything else is ruled out

Questions and answers

What does P02F9 mean?

The PCM found that the cylinder 12 injector circuit is operating outside its expected electrical range or is not performing as commanded. The cause may be the injector, its wiring or its connector.

Can I drive with code P02F9?

For a short trip to a shop, usually yes, if the engine is not running badly and the light is not flashing. Driving for long risks catalytic converter damage and wasted fuel.

How do I tell if it is the injector or the wiring?

Measure the injector resistance and test the wires to the PCM. You can also swap the injector with a neighboring cylinder: if the code follows, the injector is bad.

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.