Powertrain, generic (extended)

P236B Cylinder 12 Pressure Too Low

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P236B reports that cylinder 12 builds too little combustion pressure while its sensor circuit itself is in order. No manufacturer documents the code, because no V12 or W12 with cylinder pressure measurement has been made public. A weak peak means this cylinder lacks air, fuel or sealing: a valve that does not close fully, a worn ring pack, a head gasket leaking towards a neighbour, or an injector delivering too little. Where cylinders are numbered bank by bank, 12 shares its bank with 7 to 11, so a compression test across that whole bank is worthwhile. A gas leak past the sealing element of the pressure glow plug also lowers the value. Rough idle and the misfire code P0312 often come with it; P236C is the deviation in the other direction.

Likely causes

Intake or exhaust valve of cylinder 12 not sealing

Worn piston rings or head gasket leak

Injector delivering too little fuel

Gas leaking past the glow plug seal

Symptoms

Check engine light on
Rough idle and vibration
Misfire code for cylinder 12 stored as well

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–3,000

Time1–10 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

cylinder pressure sensor glow plugsensor wiringengine control modulefuel injector

References: law.cornell.edu, en.wikipedia.org, borgwarner.com.