What does it mean?
For the D channel to fire its coil, the module must pull the control line down from its rest voltage. P031F is set when the module commands the channel but continues to read a high voltage, so no current flows through the driver input. This is the electrical picture of an open or high resistance path, or of battery voltage being applied to the line from another circuit. The coil either does not fire at all or fires at the wrong instant, and the misfire monitor normally logs the affected cylinder at the same time, which is why cylinder specific codes often appear with this entry.
Symptoms
- Steady misfire with a rough idle and vibration
- MIL on and flashing when the engine is loaded
- Reduced power, hesitation and poor throttle response
- Hard starting, particularly when cold or damp
- Exhaust popping and a smell of unburnt fuel
- Increased fuel consumption
Likely causes
- High resistance connection or a partial break in the D control wire
- Corroded, loose or spread terminals in the coil or module connector
- Control wire shorted to battery voltage through damaged insulation
- Open igniter input in the coil or ignition module
- Poor ground for the ignition module, preventing the driver from pulling the line down
- Faulty module output stage, considered only after the wiring has been proven
How to fix it
- Read the misfire counters and freeze frame data to pin down the cylinder and the conditions
- Inspect and probe the connector terminals for tension and corrosion at both ends of the circuit
- Measure the control line voltage with the ignition on and while cranking to confirm it stays high
- Perform continuity and voltage drop tests along the control wire
- Disconnect the module and test the line for a short to a live circuit
- Check the ignition module supply, ground and fuse
- Repair the wiring or renew the coil, then clear the code and verify with a road test