Faulty ignition coil or integrated coil driver for circuit A; Damaged wiring to the ignition control circuit, such as chafing, a short to earth or an open circuit; Corroded, loose or contaminated connector at the coil or ECU; Missing or poor power or earth supply to the coil; Water ingress or heat damage in the coil connector or harness near the engine; Internal fault in the ECU ignition driver stage; Outdated or faulty ECU software where the manufacturer has issued a known fix for this code.

P030B

Ignition A Control Signal Circuit Low.

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
0B: FaultThe specific fault in that area

What it means

P030B means the engine control unit has detected a low voltage on the control signal circuit for ignition 'A'. The signal the ECU sends to command the ignition coil or driver stage is lower than expected, which suggests a short to earth, an open circuit or a faulty driver. Which coil or cylinder counts as 'A' depends on the model and engine, so check the manufacturer's data.

Symptoms

Engine warning light on
Misfire or rough running, especially at idle
Hesitation or loss of power under acceleration
Hard starting or a long crank
Poor fuel economy
Engine running in a reduced-power mode

Possible causes

Faulty ignition coil or integrated coil driver for circuit Alikely
Damaged wiring to the ignition control circuit, such as chafing, a short to earth or an open circuitlikely
Corroded, loose or contaminated connector at the coil or ECUlikely
Missing or poor power or earth supply to the coilpossible
Water ingress or heat damage in the coil connector or harness near the enginepossible
Internal fault in the ECU ignition driver stagerare
Outdated or faulty ECU software where the manufacturer has issued a known fix for this coderare

How to diagnose

Read all stored codes and the freeze frame data, noting engine speed, load and temperature when the fault set, and check for misfire codes alongside it.
Check the manufacturer's data to identify which coil or circuit is 'A' on this engine.
Inspect the coil connector, harness and ECU connector for damage, corrosion, moisture, heat damage or poor pin tension.
Check the coil power supply and earth with a multimeter, following the wiring diagram for this model.
Check the control signal wire for continuity, for a short to earth and for a short to other wires.
Look at the control signal with an oscilloscope or the live data while cranking, to see whether the ECU is sending the command.
Swap the suspect coil with a known good one, if the layout allows, and see if the fault follows the coil.
Inspect the spark plugs for wear or fouling, as these can stress the coil, and check for any applicable software updates.

How to fix

Replace the faulty ignition coil or coil driver unit.
Repair or replace damaged wiring in the ignition control circuit.
Clean or replace corroded or loose connectors and secure the terminals.
Restore the correct power or earth supply to the coil.
Replace worn or fouled spark plugs found during the checks, at the same time as the coil if advised.
Update the ECU software only if the manufacturer lists it as a fix, or repair or replace the ECU if it is confirmed faulty.

Can I keep driving?

Medium severity

The car can usually be driven a short distance to a workshop, but avoid heavy loads and high revs. A persistent misfire can overheat and damage the catalytic converter, so get it fixed soon, and stop driving if the engine light flashes.

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