What it means
Cylinder-to-cylinder pressure variation on cylinder 3 is below the calibrated minimum — pressure stays unusually constant cycle-to-cycle, often a sign that the closed-loop combustion controller has lost authority or the sensor signal is filtered.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The cylinder 3 pressure sensor records pressure changes during combustion, which the control system uses to assess that cylinder's cycles. This code sets when the measured pressure variation is unusually low, suggesting the signal is being damped or filtered, or the sensor or combustion-control system is not capturing normal cycle-to-cycle changes.
Common causes
Most likely first.
- Faulty cylinder 3 pressure sensor
- Restricted or filtered sensor signal
- Combustion control fault
- Wiring or connector fault
Symptoms
- Check engine light on
- Rough running or misfire
- Reduced power
- Uneven engine response
How to diagnose it
- Review freeze-frame data and compare cylinder 3 pressure variation with the other cylinders under similar operating conditions.
- Check live pressure data for a suspiciously flat cylinder 3 trace while engine speed and load change.
- Inspect the cylinder 3 sensor connector and harness for poor contacts, damage, or routing that could interfere with the signal.
- Check for signal filtering or related combustion-control faults using the manufacturer's diagnostic information.
- Test the cylinder 3 sensor and its circuit, comparing the output with the manufacturer's specification.
Common fixes
- Repair a poor cylinder 3 sensor connection or damaged wiring.
- Correct a harness or connector issue that is damping or interrupting the signal.
- Repair a confirmed combustion-control fault affecting cylinder 3 pressure reporting.
- Replace the cylinder 3 pressure sensor if it fails its signal test.
Can I keep driving?
If the engine runs smoothly, limit driving and avoid heavy loads until the pressure signal is checked. Rough running or reduced power warrants stopping, since inaccurate cylinder feedback can impair combustion control.
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.