What does it mean?
While ignition circuit "I" is idle the module expects to read close to supply voltage on the command line, and while the coil is being switched it expects that voltage to collapse. This code is stored when the line stays above the calibrated upper threshold even during the switching window, so the module never sees the voltage drop that proves current is flowing.
In practice that points either to an interruption on the ground side of the circuit or to an unintended connection to a live feed that holds the line up. Because a stuck high command line cannot deliver a controlled spark, the affected cylinder stops firing correctly and the module logs the fault together with the MIL (check engine lamp).
The strategy usually needs the condition to be present over several ignition events before the code matures, which is why the fault can appear only under vibration or heat.
Symptoms
- MIL (check engine lamp) on, frequently accompanied by a misfire code for the corresponding cylinder
- Engine shakes at idle and smooths out only partially as revs rise
- Hesitation and a hollow feeling when accelerating, worst at low speed in a high gear
- Difficult starting, sometimes needing a second attempt when the engine is cold
- Smell of unburned fuel and a gradual drop in fuel economy
- Warning lamps for traction or stability may appear on some vehicles as the misfire upsets torque delivery
Likely causes
- Command wire shorted to battery voltage, often against a feed wire inside a damaged loom or after an incorrect accessory installation
- Open ground path for the coil or igniter, including a loose or corroded ground eyelet on the engine
- High resistance or broken connection inside the coil that prevents current from flowing when the module switches
- Corroded terminals in the coil connector adding enough resistance to keep the line artificially high
- Water tracking between adjacent pins in a flooded connector, feeding voltage into the command circuit
- Faulty control module output stage that fails to pull the line down, considered last
How to fix it
- Read the freeze frame and confirm whether the code appears only when cold, only when hot, or on rough road surfaces
- Disconnect the coil, turn the ignition on and measure the command pin against ground; battery voltage present with the module not commanding the output indicates a short to a live feed
- Check the coil supply and ground path, cleaning and retightening any engine ground eyelet that shows corrosion
- Measure the coil primary resistance and compare it against another coil on the same engine to expose an internal open or high resistance
- Trace the harness for damage where it passes near power feeds, and separate any aftermarket wiring that has been tapped into the ignition loom
- Inspect and dry the connector, replacing corroded terminals rather than simply reseating them
- After repair, clear the code, let the engine reach full temperature and road test through the recorded conditions to confirm the output now switches normally