What does it mean?
When the control module releases ignition circuit "J" the wire should sit near supply voltage, and when the module switches the output the voltage should collapse toward ground as current builds in the coil. This code is set when the monitored voltage stays above the calibrated high threshold even while the output is commanded, so the expected collapse never occurs. That behaviour points to an interruption on the ground or load side of the circuit, or to a foreign voltage source holding the line up. Without a controlled current path the coil never charges, the cylinder loses its spark and combustion in that cylinder stops. The module records the fault, generally disables the output to protect the driver stage, and turns on the MIL (check engine lamp).
Symptoms
- MIL (check engine lamp) on, generally with a cylinder specific misfire code stored at the same time
- Rough idle that does not fully clear as engine speed rises
- Noticeable lack of power and hesitation when accelerating from low revs
- Hard starting, occasionally requiring a second crank when cold
- Unburned fuel smell and rising fuel consumption
- Jerky running under steady throttle and, on some vehicles, a stability or traction warning triggered by uneven torque
Likely causes
- Command wire touching a permanently live feed inside a chafed loom or through a badly executed accessory connection
- Open or high resistance ground for the coil pack or igniter, including a loose engine ground strap
- Coil with an internally open or high resistance primary winding that prevents current flow
- Heavily corroded terminals in the coil connector adding series resistance to the circuit
- Water bridging adjacent pins in a flooded connector and feeding voltage into the command line
- Broken conductor in the command wire that leaves the module pin floating at its internal pull up level
- Control module output stage unable to pull the line low, considered only after all external checks pass
How to fix it
- Read the freeze frame and establish whether the fault appears cold, hot or only on rough roads
- Disconnect the coil, switch the ignition on and check the command pin for unexpected battery voltage, which would indicate contact with a live feed
- Verify the coil supply and its ground path, cleaning and retorquing any corroded engine ground point
- Measure the primary winding resistance of the suspect coil and compare it directly with a coil from a different cylinder on the same engine
- Inspect the harness where it runs alongside power cables and separate any aftermarket wiring spliced into the ignition loom
- Clean or renew corroded terminals in the coil connector instead of merely reseating them
- Repair the fault found, clear the memory and confirm on a road test at the recorded load and speed that the output now switches correctly