Powertrain, generic (extended)

P236E Cylinder 12 Pressure Variation High

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P236E means the pressure signal of cylinder 12 scatters more than the ECM tolerates, either within one cycle or from one cycle to the next. No manufacturer publishes the code; the reference is Saab's P039D for cylinder 1, a Type B fault that needs only 0.2 s outside its window. Two groups of causes are possible. Electrical ones make the trace noisy: interference coupled into the signal wire, or a low-reference contact whose resistance changes with vibration. Combustion-related ones make the cylinder really unsteady: an injector whose delivery varies shot by shot, air in the fuel, or a sticking valve. Live data that are noisy even on overrun, when nothing burns, point to the electrical side. Drivers notice slight roughness at most.

Likely causes

Interference on the signal wire

Low-reference contact with changing resistance

Injector delivery varying from shot to shot

Air in the fuel supply

Symptoms

Check engine light on
Occasional slight roughness

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€80–900

Time1–4 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: saabwisonline.com, law.cornell.edu.