What does it mean?
Ignition B is the second ignition control channel the engine control module drives. On coil-on-plug engines it triggers a single coil, while on waste-spark systems one channel fires two cylinders at once, so a failure here can silence a pair of cylinders. The module expects to see the coil driver input as an electrical load on that line. P030D is stored when the load is missing entirely: the trigger is commanded but no current can flow, which is the electrical picture of an open circuit somewhere between the module output and the coil input. The affected coil never fires, so the misfire monitor normally records the corresponding cylinders as well.
Symptoms
- Steady misfire on the cylinder or cylinder pair served by this channel
- MIL on and frequently flashing when the engine is loaded
- Heavy shaking at idle and a clear loss of power when accelerating
- Hard starting and, on engines with few cylinders, a possible no-start
- Fuel smell from the exhaust and a risk of overheating the catalytic converter
- Cylinder specific misfire codes stored with this entry
Likely causes
- Break in the ignition B control wire, often at a flexing point or at an old repair splice
- Coil or ignition module connector unplugged, damaged, or with a terminal pushed out of the housing
- Open input stage inside the coil's integrated igniter
- Connector corrosion caused by oil or water sitting in the spark plug well
- Harness chafed through where it crosses the cam cover or a bracket
- Loss of supply voltage or ground at the ignition module so its input stage cannot present a load
- Module ignition driver failure, considered last
How to fix it
- Match the cylinder misfire counters with the coil the B channel drives before starting any repair
- Inspect the coil connector, spark plug well and harness for oil, corrosion and chafe damage
- Test continuity from the module pin to the coil pin and flex the harness during the measurement to expose an intermittent break
- Check coil supply voltage and the quality of the ground at the connector
- Use an oscilloscope to confirm the module produces a trigger pulse on this channel while cranking
- Move the coil to a known good position and re-test to see whether the fault follows the component
- Repair the open circuit or renew the coil, then clear the code and verify with a road test under load