P03FC Ignition K Control Signal Circuit High

Ignition K is one of up to twelve control signal lines (A to L) from the engine module to an ignition coil with integrated output stage or to an ignition module – plausibly the 11th channel, but the code standard leaves the assignment to the manufacturer. The code concerns this logic-level signal, not the coil's primary circuit (coil K has its own codes, P0361 and P2330 ff). P03FC means the signal stays too high – typically the control line is shorted to battery voltage or another supply, so the driver cannot pull it low. The coil fires wrongly or not at all; the misfire usually also sets P0300 ff, and many modules shut off injection to that cylinder to protect the catalyst. No manufacturer document available to us uses this code – it would only concern twelve-cylinder engines, whose makers publish no OBD summaries; GM and Ford tables stop at eight and ten cylinders.

Likely causes

Symptoms

• Check engine light on, may flash with severe misfire
• Misfire on the cylinder of this channel, rough running
• Loss of power, cylinder possibly shut off

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, patents.google.com, gsi.ext.gm.com.