What does it mean?
Ignition D is the fourth ignition control channel. Where an external ignition module drives several coils, all the channels share power and ground, so a fault that affects only the D channel almost always sits in that channel's own control wire or in the input stage it feeds. P031D is stored when the module finds no electrical load at all on the D control line: the trigger is commanded but no current can flow. That is an open circuit, which can be a broken wire, a terminal that has lost contact, or an open input inside the coil or ignition module. The coil concerned never fires and the cylinder it serves goes dead.
Symptoms
- Dead cylinder with a steady misfire and heavy vibration at idle
- MIL on and flashing under load
- Marked loss of power and poor acceleration
- Difficult starting, sometimes needing extended cranking
- Fuel smell from the exhaust and rising catalytic converter temperature
- Cylinder specific misfire codes stored alongside
Likely causes
- Broken D channel control wire, or a failed splice from an earlier repair
- Terminal pushed out of the connector housing, or a connector that is not fully latched
- Open igniter input inside the coil or ignition module
- Connector corrosion from water ingress or oil in the spark plug well
- Harness chafed through on a bracket, cover edge or moving part
- Coil supply or ground missing, so the input stage cannot present a load
- Module ignition driver failure, treated as the last possibility
How to fix it
- Establish which cylinder the D channel serves from the misfire counters before any parts work
- Inspect the connector and harness closely: check the latch, terminal seating, corrosion and chafe points
- Test continuity from the module pin to the coil pin, flexing the harness to catch an intermittent break
- Confirm supply voltage and a good ground at the coil or ignition module
- Use an oscilloscope to check whether a trigger pulse leaves the module on this channel while cranking
- Swap the coil to another position to see whether the fault moves with the part
- Repair the open circuit or renew the faulty component, then clear the code and verify under load