Powertrain, generic (extended)

P236D Cylinder 12 Pressure Variation Low

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P236D is stored when the cylinder 12 pressure trace swings too little – the curve stays flatter than compression and combustion ought to make it. No manufacturer documents this code for a twelve-cylinder engine. In Saab's 9-5 diesel the comparable cylinder-1 code P039C exists in three sub-variants, 00, 01 and 02, a sign that the ECM tells apart several ways in which a signal can be too weak. The likely culprits sit in the sensor: in BorgWarner's design a flexible heater rod passes the pressure on to a measuring diaphragm, so carbon that grips the rod dampens the signal, and ageing circuitry in the head of the plug lowers its amplification. If compression itself were missing, P236B would be the more likely entry. Driving is normally unaffected.

Likely causes

Carbon deposits restricting the heater rod

Sensor electronics with reduced gain

Actual low compression in cylinder 12

Symptoms

Check engine light on
Flat pressure curve for cylinder 12 in live data

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€100–600

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 module

References: saabwisonline.com, borgwarner.com.