What it means
Ion current from cylinder 5 is above the expected window. Cross-coupled signal, biased reference, or sensor fault.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The ECM uses the post-spark ion-current signal at cylinder 5's plug to assess combustion. This code sets when that signal is higher than expected, which can happen if ignition-coil interference couples into the sense wire or its reference is biased.
Common causes
Most likely first.
- Inductive cross-coupling from ignition coil primary
- Sense reference voltage biased
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light on
- Rough idle or engine misfire
- Reduced engine performance
How to diagnose it
- Review freeze-frame and live ion-sense data to confirm the high reading is isolated to cylinder 5 and identify the conditions when it occurs.
- Inspect cylinder 5's ion-sense connector for corrosion, loose pins, or contamination that could disturb the signal reference.
- Check whether cylinder 5's sense wire is routed alongside or damaged by ignition-coil primary wiring, a potential source of inductive cross-coupling.
- Inspect the cylinder 5 sense reference and wiring for unintended voltage bias or shorts, using the manufacturer's circuit information.
- Test the reference and sensing path against the manufacturer's specification; replace the sensor or module only if those checks isolate an internal fault.
Common fixes
- Clean and secure corroded or loose cylinder 5 connector contacts.
- Repair damaged cylinder 5 sense wiring and restore separation from ignition-coil wiring as specified.
- Repair a confirmed fault in the cylinder 5 sense reference circuit.
- Replace the faulty cylinder 5 ion-sense element or module if testing confirms it is producing a high-biased signal.
Can I keep driving?
If the engine runs smoothly, keep trips short and avoid hard acceleration until the cylinder 5 signal is checked; the ECM may assess combustion incorrectly and emissions can rise. Stop if the engine develops a severe misfire or marked power loss.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.