What does it mean?
On the ignition A control channel the module output rests at a defined voltage and only pulses when a spark is due. P030B is stored when the module measures a voltage below its low threshold on that channel at a time when the line should be at rest, which is what a short to ground or an internally shorted igniter input looks like. To protect its output transistor the module normally disables the channel once the fault is confirmed, so the coil concerned stops firing altogether. Unlike the open circuit version of this fault, here a current path does exist, but it leads somewhere it should not.
Symptoms
- Persistent misfire on the affected cylinder or coil group, with the MIL on
- The engine shakes at idle and feels flat under acceleration
- Hesitation, jerking and sometimes a bang from the exhaust under load
- Hard starting, and on some engines a no-start if the channel serves several cylinders
- Raw fuel smell and a risk of overheating the catalytic converter
- Reduced power or limp mode with a restricted engine speed on some vehicles
Likely causes
- Ignition control wire shorted to ground through chafed insulation
- Internal short in the coil igniter or in the ignition module input stage
- Water, coolant or oil in the coil connector bridging the control pin to a ground pin
- Harness pinched under a bracket, cam cover or trim panel after previous work
- Melted insulation where the ignition harness runs close to the exhaust manifold
- Module ignition driver shorted internally, confirmed only after the external circuit has been cleared
How to fix it
- Check the freeze frame data and the misfire counters to establish which cylinders are involved
- Unplug the coil or ignition module: if the low voltage disappears at the module connector the component is shorted, if it remains the harness is grounded
- Measure resistance from the control wire to ground with both ends disconnected; a low reading proves the short
- Trace the harness along its whole route, paying attention to points where it passes near the exhaust and moving parts
- Inspect the coil connector for oil, coolant or corrosion and check the spark plug tube seals if oil is present
- Substitute a known good coil to see whether the fault follows the part
- Repair the shorted wire with a properly insulated joint, then clear the code and check the misfire counters over a road test