Powertrain, generic (extended)

P234F Cylinder 9 Pressure Variation Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P234F flags that the pressure signal of cylinder 9 changes too little: the rise and fall the ECM expects across each combustion cycle is missing or very small. For cylinder 9 there is no manufacturer documentation. In the Saab 9-5 with GM's 2.0 CDTI, the cylinder-1 analogue is P039C, labelled pressure variation too low, with three sub-faults; it reacts after more than 0.2 s out of range with the engine running and is grouped with the erratic code as a signal performance fault. Saab does not explain the exact measurement. A flat signal fits a sensing pin stuck in carbon that no longer passes on the pressure, a sensor that has lost sensitivity, or a cylinder that hardly builds up pressure. Usually only the warning lamp shows; the high counterpart is P2350.

Likely causes

Sensing element of the glow plug stuck by carbon
Sensor lost sensitivity through ageing
Cylinder 9 builds up little pressure (compression or injection fault)

Symptoms

  • Check engine light on
  • Usually no change in engine behaviour

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–500
Time1–3 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

Related codes

P2350P234CP2349P039CP2359

References: saabwisonline.com, law.cornell.edu, borgwarner.com.