Faulty ignition coil or coil driver stage on the 'B' circuit; Damaged, chafed or corroded wiring in the ignition control signal circuit, such as a short to earth; Poor connection at the coil connector or control unit connector (loose, corroded or spread terminals); Worn spark plugs or high plug gap causing coil stress and abnormal circuit readings; Low or unstable supply voltage or poor earth to the coil or ignition module; Fault inside the engine control unit's ignition output driver.

P030E

Ignition B 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
0E: FaultThe specific fault in that area

What it means

P030E means the engine control unit has detected a low voltage on the control signal circuit for ignition 'B'. This is the circuit that tells an ignition coil, coil driver or ignition module when to fire. Which cylinder or coil bank 'B' refers to depends on the engine and layout, so check the wiring diagram for the vehicle. The fault sets when the commanded signal does not match the voltage the control unit sees, which points to a short to earth, an open circuit or a faulty driver.

Symptoms

Engine management light on
Misfire, rough running or shaking at idle
Hesitation or loss of power under load
Hard starting or intermittent no-start
Poor fuel economy
Possible limp mode, or flashing warning light if misfiring is severe

Possible causes

Faulty ignition coil or coil driver stage on the 'B' circuitlikely
Damaged, chafed or corroded wiring in the ignition control signal circuit, such as a short to earthlikely
Poor connection at the coil connector or control unit connector (loose, corroded or spread terminals)likely
Worn spark plugs or high plug gap causing coil stress and abnormal circuit readingspossible
Low or unstable supply voltage or poor earth to the coil or ignition modulepossible
Fault inside the engine control unit's ignition output driverrare

How to diagnose

Read all stored and pending codes and freeze frame data, noting engine load, speed, temperature and whether any misfire codes are also set.
Check the wiring diagram to find which coil or module is 'B' for this engine, as this varies by model.
Visually inspect the coil connector, wiring and harness for heat damage, chafing, oil contamination, water ingress and corrosion.
Check the coil supply voltage and earth with the ignition on, and check for voltage drop under load.
Swap the suspect coil with a known-good one on another cylinder (if the layout allows) and see whether the fault follows the coil.
Back-probe the control signal with a multimeter or oscilloscope while cranking, and check for a short to earth or an open circuit with the connectors unplugged.
Inspect the spark plugs for wear, incorrect gap, fouling or damage, and replace if they are out of specification.
If wiring, supply and coil all test good, consider the control unit driver, and check for relevant software updates for the model.

How to fix

Replace the faulty ignition coil or ignition module, and fit new spark plugs if they are worn.
Repair or replace damaged wiring and fix any short to earth or open circuit in the control signal wire.
Clean, repair or replace corroded or loose connector terminals and secure the connector properly.
Restore the power supply or earth connection if voltage drop or a poor earth is found.
Repair or replace the engine control unit only after all other causes are ruled out, and carry out any programming the manufacturer requires.

Can I keep driving?

Medium severity

Avoid driving for long, and avoid heavy loads, until it is repaired. Unburnt fuel from a misfire can overheat and damage the catalytic converter, so stop if the warning light flashes or the engine runs badly.

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