P234A Cylinder 9 Pressure Sensor Circuit Low

P234A means the signal of the cylinder 9 combustion pressure sensor stays below its permitted minimum. No published manufacturer document covers cylinder 9; the closest pattern is the GM-built 2.0 CDTI diesel of the Saab 9-5, whose cylinder 1–4 low codes (P0397 for cylinder 1) set after more than 2 s below threshold with the engine running, checked once per operating cycle, as Type B – the MIL comes on after the second failing trip. A scan tool then shows a peak pressure of 0 kPa. Electrically this points to a lost 5 V reference, a reference shorted to ground or a signal wire touching ground. Saab expects 3 to 12 Ohm between reference and ground at the plug. Combustion control for the cylinder is suspended, which usually goes unnoticed. The high counterpart is P234B.

Likely causes

Symptoms

• Check engine light after two trips
• Peak pressure reads 0 kPa on the scan tool
• Driving behaviour mostly unchanged

Repair estimate

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

Parts involved

Related codes

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