Open circuit or high resistance in the wiring between the ECU and the coil K control input; Poor connection or corroded, loose or pushed-out terminal at the coil K connector; Faulty ignition coil K, or a coil with an internal driver that has failed open; Damaged wiring loom from heat, chafing or rodent damage near the engine; Missing or open power or earth supply to the coil, which stops the coil responding to the control signal; Fault in the ECU ignition output driver.

P03FA

Ignition K Control Signal Circuit/Open.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
3: AreaIgnition system or misfire
FA: FaultThe specific fault in that area

What it means

P03FA means the engine control unit has detected an open circuit on the control signal for ignition coil 'K'. The ECU commands the coil driver or ignition control output and sees no valid current or feedback, so it assumes the circuit is broken. Which cylinder 'K' refers to depends on the engine and the manufacturer's coil lettering, so confirm this from model-specific data.

Symptoms

Engine warning light on
Misfire or rough running, especially at idle or under load
Hesitation or loss of power
Hard starting or extended cranking
Raw fuel smell or poor fuel economy
Flashing warning light under load if the misfire is severe

Possible causes

Open circuit or high resistance in the wiring between the ECU and the coil K control inputlikely
Poor connection or corroded, loose or pushed-out terminal at the coil K connectorlikely
Faulty ignition coil K, or a coil with an internal driver that has failed openlikely
Damaged wiring loom from heat, chafing or rodent damage near the enginepossible
Missing or open power or earth supply to the coil, which stops the coil responding to the control signalpossible
Fault in the ECU ignition output driverrare

How to diagnose

Read all stored codes and freeze frame data to see engine load, speed and temperature when the fault set, and note any related misfire codes.
Identify which cylinder and coil 'K' is on this engine using model-specific wiring and layout data.
Inspect the coil K connector and the nearby loom for damage, corrosion, water ingress, bent or loose terminals, and heat or chafing damage.
Clear the code and see if it returns. Check whether it comes back at once or only with vibration, heat or damp.
Check the coil's power supply and earth with a multimeter, following the wiring diagram for this engine.
With the ECU and coil connectors disconnected, test the control wire for continuity and for shorts to earth or supply.
Swap coil K with a known good coil, if the layout allows, and see whether the fault follows the coil.
Check the ECU output signal with a scope or suitable tester once the wiring and coil are proven good.

How to fix

Repair or replace the damaged wiring between the ECU and coil K, using proper soldered and sealed joints.
Clean, re-seat or repair the connector terminals, and replace the connector if it is damaged.
Replace ignition coil K if it fails testing or the fault follows the coil.
Restore the correct power or earth supply to the coil by repairing the supply circuit.
Replace or repair the ECU only after all wiring and the coil have been proven good, and only if the manufacturer's procedure calls for it.

Can I keep driving?

Medium severity

Short, gentle journeys are possible, but get it checked soon because unburnt fuel from a misfire can damage the catalytic converter. If the warning light flashes or the engine runs badly, stop driving and have it recovered.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.