What does it mean?
The module drives ignition circuit "I" with a low side switch and expects the line to sit near system voltage while the coil is charging and to be pulled down only during the commanded switching window. Monitoring the voltage on that line is how the module verifies its own output stage as well as the integrity of the harness that runs to the coil.
This code is set when the measured voltage on the "I" command line stays below the calibrated low threshold at a moment when the module is not commanding it low. Such a reading means an unwanted path to ground exists somewhere between the module pin and the coil, or the driver stage itself is conducting continuously. The result is an ignition output that can no longer be timed accurately, so the module normally disables it and turns on the MIL (check engine lamp).
Symptoms
- MIL (check engine lamp) on, in many cases with a misfire code for the cylinder fed by that coil
- Rough, uneven idle and a lumpy exhaust note
- Loss of power and poor throttle response, especially climbing a hill or accelerating with a load
- Occasional backfire or popping through the exhaust as unburned mixture reaches the converter
- Extended cranking or an engine that starts and then stumbles for the first seconds
- Fuel consumption noticeably higher than usual
Likely causes
- Short to ground in the command wire, usually where the insulation has worn through against the cylinder head, a bracket or a clamp
- Coolant or oil that has entered the coil connector and bridged the command pin to the sensor ground or to the housing
- Internally shorted ignition coil whose primary winding has failed to its own core
- Chafed harness inside a loom that has flattened under a retaining clip and made intermittent contact with the body
- Damaged connector seal letting road salt and moisture create a low resistance leakage path
- Shorted driver transistor in the control module, checked only after the harness has been isolated and proven clean
How to fix it
- Note the freeze frame conditions and check whether related coil or misfire codes appeared at the same moment
- Unplug the coil on the "I" circuit and measure resistance from the command pin on the harness side to a clean chassis ground; a low reading with the coil disconnected proves the short is in the wiring
- If the harness reads open with the coil unplugged, measure the coil primary winding and check it for insulation breakdown to the case
- Follow the harness branch by hand along the head and the loom clips, looking for flattened, melted or rubbed sections that touch metal
- Inspect the connector cavities for oil and coolant, and confirm the seal and the terminal locks are intact
- Repair or replace the damaged wire section rather than patching it with tape, then reconnect and watch the ignition output on live data while the engine idles
- Clear the fault memory and confirm the code does not return during a drive that reproduces the freeze frame load and speed