Faulty ignition coil or integrated coil driver pulling the control signal high; Control signal wire shorted to a voltage supply or chafed against other live wiring; Damaged, corroded or loose connector at the coil or control unit; Open circuit or high resistance in the signal return or earth side, causing a high voltage reading; Poor power or earth supply to the coil, caused by a fault in the supply or earth circuit; Fault inside the engine control unit's ignition driver; Previous poor repair or aftermarket wiring interfering with the ignition circuit.

P030C

Ignition A Control Signal Circuit High.

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
0C: FaultThe specific fault in that area

What it means

P030C means the engine control unit has seen a voltage higher than expected on the ignition 'A' control signal circuit, the line that triggers an ignition coil or coil driver. Which cylinder or coil 'A' refers to depends on the model and engine, so check the wiring diagram for the vehicle. The fault is usually a wiring, coil driver or control unit issue, and it may be accompanied by misfire codes.

Symptoms

Engine management light on
Misfiring, rough running or hesitation
Hard starting or long cranking
Loss of power or limp-home behaviour
Poor fuel economy
Flashing warning light under load if misfire is severe

Possible causes

Faulty ignition coil or integrated coil driver pulling the control signal highlikely
Control signal wire shorted to a voltage supply or chafed against other live wiringlikely
Damaged, corroded or loose connector at the coil or control unitlikely
Open circuit or high resistance in the signal return or earth side, causing a high voltage readingpossible
Poor power or earth supply to the coil, caused by a fault in the supply or earth circuitpossible
Fault inside the engine control unit's ignition driverrare
Previous poor repair or aftermarket wiring interfering with the ignition circuitrare

How to diagnose

Read all stored codes and freeze frame data, noting engine load, temperature and speed when the code set, and check for misfire codes alongside.
Check the vehicle wiring diagram to identify which coil or circuit is Ignition A on this engine.
Inspect the coil connector, wiring and control unit connector for damage, corrosion, moisture, bent pins, chafing and heat damage.
Check the coil supply voltage and earth with the ignition on, following the manufacturer's procedure.
Check the control signal wire for a short to voltage and for continuity back to the control unit, with the connectors disconnected.
Swap the suspect coil with a known good one on another cylinder, clear the code and see if the fault follows the coil.
Use a scope or suitable tester to look at the control signal while cranking or running and compare it with the expected pattern.
Only suspect the control unit once the coil, wiring, supply and earth are confirmed good.

How to fix

Replace the faulty ignition coil or coil driver.
Repair or replace shorted, chafed or damaged signal wiring.
Clean, repair or replace faulty connectors and terminals.
Restore a good power supply and earth to the coil circuit.
Repair or replace the engine control unit if it is confirmed faulty, and have it coded to the vehicle as needed.
Clear the codes and road test to confirm the fault does not return.

Can I keep driving?

Medium severity

Short, gentle journeys may be possible, but fix it soon. Persistent misfire can overheat and damage the catalytic converter, so avoid hard driving, and stop if the warning light flashes.

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