P236E: Cylinder 12 Pressure Variation High

What it means

Cylinder-to-cylinder pressure variation on cylinder 12 is above the calibrated maximum — combustion is unstable cycle-to-cycle, typical of partial misfire or injector seat erosion.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The engine controller tracks pressure changes in cylinder 12 from one combustion cycle to the next. P236E sets when that variation exceeds the calibrated maximum, indicating unstable combustion that may come from an intermittent misfire or inconsistent injector delivery.

Common causes

Most likely first.

1. Unstable combustion in cylinder 12
2. Cylinder 12 injector delivery fault
3. Intermittent misfire

Symptoms

• Check-engine light
• Rough running or misfire
• Engine vibration
• Reduced engine power

How to diagnose it

1. Save freeze-frame data and check which engine speed and load coincide with the high cylinder 12 pressure variation.
2. Compare cylinder 12 pressure traces and misfire counts with other cylinders to see whether the instability is isolated to cylinder 12.
3. Inspect the cylinder 12 sensor connector, mounting, and wiring for loose contacts or damage that could create a false changing signal.
4. Check cylinder 12 injector operation and its wiring for inconsistent delivery using the manufacturer's diagnostic procedure.
5. Investigate ignition, compression, and other combustion causes on cylinder 12 if the sensor and injector checks do not explain the variation.

Common fixes

• Repair loose or damaged wiring at the cylinder 12 pressure sensor.
• Repair or replace the cylinder 12 injector if tests confirm inconsistent fuel delivery.
• Correct an ignition fault or other confirmed cause of intermittent cylinder 12 misfire.
• Repair a mechanical cylinder 12 problem if compression or leak-down testing identifies one.

Can I keep driving?

Avoid hard acceleration and towing while cylinder 12 combustion is unstable. Stop if the engine misfires continuously or vibrates severely, since continued misfire can damage the exhaust system and worsen engine performance.