P236F: Cylinder 12 Combustion Performance

What it means

The closed-loop combustion controller reports that combustion performance on cylinder 12 is below the calibrated quality metric. Computed from the cylinder pressure trace — IMEP (indicated mean effective pressure), CA50 (50% mass burnt angle) or peak pressure deviates from the model.

At a glance

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

How it works

The engine controller assesses cylinder 12 combustion using pressure-trace measures such as the cylinder's pressure and the timing of heat release. P236F sets when the controller judges cylinder 12's combustion performance to be outside its calibrated model, so the pressure data and related engine-control inputs need to be checked together.

Common causes

Most likely first.

1. Mean effective pressure outside model
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Check-engine light
• Rough running or misfire
• Reduced engine power
• Poor acceleration

How to diagnose it

1. Save freeze-frame data and review cylinder 12 pressure, misfire, and engine operating data to identify when performance fell outside the model.
2. Compare cylinder 12 pressure-trace information with the other cylinders and check for related combustion or communication codes.
3. Inspect the cylinder 12 sensor mounting, connector, and wiring for faults that could make its pressure trace inaccurate.
4. Check cylinder 12 injector and ignition operation using the manufacturer's procedures to rule out a real combustion problem.
5. If the cylinder readings appear sound but the fault persists, check relevant module communication and network wiring according to the manufacturer's diagnostic process.

Common fixes

• Repair a confirmed cylinder 12 sensor wiring, connector, or mounting fault.
• Repair the cylinder 12 injector or ignition fault if testing identifies one.
• Correct a verified network wiring or module communication fault affecting the reported cylinder data.
• Replace a pressure sensor or module only when manufacturer-guided testing confirms it is faulty.

Can I keep driving?

Limit driving if the engine runs rough or has reduced power, and avoid heavy loads until the cause is known. Stop if misfiring becomes severe; the fault may reflect a real cylinder 12 combustion problem that can worsen with continued use.