Ignition

P03FA — Ignition K Control Signal Circuit Open

Severity: medium Drive with care, to a shop

What P03FA means

P03FA means the engine control module (ECM) detected an open or fault in the Ignition K control signal circuit between the ECM and the ignition coil or control module. The ECM normally sends timed pulses over this circuit so the coil builds energy and fires the spark plug at the right moment. If the signal does not get through, that cylinder may lose spark or fire erratically.

Symptoms

  • Check Engine light is on
  • Engine misfire or rough running
  • Hesitation or reduced power
  • Poor fuel economy
  • Possible stalling or hard starting

Possible causes

  1. Open or short in the Ignition K control signal wiring
  2. Corroded, loose or damaged connector terminals
  3. Faulty ignition control module or coil
  4. Damaged wiring harness (chafing, heat, rodents)
  5. Faulty ECM (uncommon)

How to diagnose

  1. Scan all codes and freeze frame data, and note any misfire codes
  2. Inspect the wiring and connectors at the coils or ignition module for damage, corrosion or heat marks
  3. Use the wiring diagram to find the Ignition K signal circuit and check power and ground at the coil or module connector
  4. Test the wire from the ECM to the module for continuity, and for shorts to ground or voltage
  5. Use a scope or test light to confirm control pulses reach the coil
  6. Swap the coil or module with a known good one to see if the problem follows it
  7. If wiring and module are good, check the ECM, starting with its power and grounds

Common fixes

  • Repair the wire or replace the damaged harness section
  • Clean or replace the connector and terminals
  • Replace the faulty ignition module or coil
  • Replace or reprogram the ECM only after it is confirmed faulty

Questions and answers

What does P03FA mean?

It means an open or fault in the Ignition K control signal circuit between the ECM and the ignition module or coil. A cylinder may lose spark as a result.

Can I drive with code P03FA?

Only briefly and carefully, for example to a shop. Misfires can damage the catalytic converter, and the engine may stall at a bad moment.

Where should I start diagnosing P03FA?

Start with a visual check of the wiring and the coil or module connector. Wiring and connector problems are more common than a failed ECM.

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.