What it means
Ion current from cylinder 10 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 ion-sensing system reads post-spark electrical activity through the spark plug in cylinder 10 to assess combustion. P28B7 sets when the module sees a signal above the expected window for that cylinder, which can happen if ignition-coil interference couples into the sense line 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
- Engine misfire or rough running
- Reduced power
How to diagnose it
- Record freeze-frame data and check cylinder 10 ion-sense data and misfire counts to identify the conditions when the signal is high.
- Inspect cylinder 10's sense wiring routing near the ignition coil and look for damaged insulation, poor shielding, or connector corrosion.
- Check the sense reference and connector contacts for an unintended bias or high resistance using the wiring diagram and manufacturer's specification.
- Compare the cylinder 10 signal with other cylinders while observing whether it changes with ignition operation, if supported by the scan tool.
- Test the cylinder 10 sense circuit and module for cross-coupling or an internal fault using the manufacturer's diagnostic procedure.
Common fixes
- Clean and secure corroded cylinder 10 sense connector pins.
- Repair damaged insulation or reroute the cylinder 10 sense wire as specified to reduce ignition-coil coupling.
- Repair the biased sense-reference connection or wiring fault identified by testing.
- Replace the ion-sense module or sensor element if tests confirm an internal fault.
Can I keep driving?
If the engine runs normally and the warning light is steady, keep trips short and gentle until the signal fault is diagnosed; an inaccurate cylinder 10 reading can obscure a real misfire and increase emissions. Stop driving if the engine runs roughly, power drops significantly, or the light flashes.
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.