Powertrain, generic (extended)

P236A Cylinder 12 Pressure Sensor Circuit Intermittent/Erratic

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P236A covers brief, irregular disturbances of the cylinder 12 pressure signal – faults that come and go without settling into a lasting low or high state. Its model is the Saab 9-5 diesel code P0399, which responds as soon as the signal stays outside its band longer than 0.2 s. No manufacturer publishes P236A itself, since no twelve-cylinder engine with pressure glow plugs is documented. Volkswagen's 2014 bulletin for 2.0 TDI engines gives a practical routine for such cases: watch the maximum pressure value of every cylinder while flexing harness and connectors, and swap the suspect glow plug with one from a neighbouring cylinder. If the fault follows the plug, the plug is bad; if not, the harness is. Up to two drive cycles may pass before the lamp returns.

Likely causes

Loose or corroded terminal in the plug connector

Harness rubbing through under engine vibration

Glow plug sensor with intermittent internal fault

Symptoms

Warning lamp that switches on and off over several days
Pressure value of cylinder 12 jumps when the harness is moved

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€40–600

Time0.5–4 h

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

Parts involved

cylinder pressure sensor glow plugsensor wiringengine control module

References: saabwisonline.com, static.nhtsa.gov, law.cornell.edu.