P28B9
Cylinder 11 Ion Current Sense Circuit Range/Performance
The ion current signal from cylinder 11 is outside the expected range for combustion conditions. Combustion quality cannot be assessed reliably.
The ion current signal from cylinder 11 is outside the expected range for combustion conditions. Combustion quality cannot be assessed reliably.
Common causes
- high
Spark plug aged - electrode shape changed
One of the most commonly reported causes for this code — check this first.
Typical part cost: $110-770
- medium
Ion sense circuit gain drift
A plausible cause — test and verify before replacing parts.
Typical part cost: $110-770
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First things to check
- 1Confirm the code with a scan tool and check for additional related codes.
- 2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.
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Related codes
See related trouble codes
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Frequently asked questions
What does P28B9 mean?
P28B9 means "Cylinder 11 Ion Current Sense Circuit Range/Performance". It is a generic OBD-II code that points to a fault in the auxiliary emission controls.
What are the most common causes of P28B9?
spark plug aged - electrode shape changed; ion sense circuit gain drift; sensor element aged beyond calibration window — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.
Can I keep driving with this code?
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical. Use the Wrenchify app for a full diagnosis specific to your vehicle.
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