What does it mean?
The ignition B control line should sit at its rest voltage and drop only at the moment the module triggers a spark. P030E is stored when the module reads a voltage below its low threshold outside that trigger window, which indicates the line is being grounded somewhere or that the coil driver input has shorted internally. Because the module protects its own output stage, it commonly shuts the channel down once the fault is confirmed, so the coil stops firing and the cylinders it serves go dead. On waste-spark engines two cylinders are affected together, which produces a very obvious, evenly spaced misfire pattern.
Symptoms
- Constant misfire on the affected cylinder or pair, with a rhythmic shake at idle
- MIL on and often flashing under load
- Jerking, hesitation and loss of power during acceleration
- Difficult starting and an unstable idle speed
- Smell of unburnt fuel and occasional popping from the exhaust
- Limp mode with a limited engine speed on some vehicles
Likely causes
- Control wire grounded where the insulation has worn away against a bracket or the cylinder head
- Internal short in the coil igniter or in the ignition module input
- Coolant or oil in the coil connector bridging pins together
- Harness pinched under a clip, cover or wiring loom bracket after previous service work
- Insulation melted where the loom runs close to the exhaust manifold or the turbocharger
- Faulty module driver stage, confirmed only after the external circuit has been cleared
How to fix it
- Note which cylinders show misfire counts and confirm they belong to the B channel
- Unplug the coil and see whether the low voltage disappears at the module connector, which separates a shorted component from a grounded wire
- Measure resistance between the control wire and ground with both ends disconnected
- Follow the harness along its full length, checking clips, brackets and hot areas for chafe and melting
- Inspect the connector and the plug well for oil or coolant and renew the tube seals if they are contaminated
- Fit a known good coil temporarily to see whether the fault follows the part
- Repair the short with a soldered, insulated joint, then clear the code and check the misfire counters on a road test