P03AC Cylinder 3 Pressure Sensor Circuit High

Some diesels have a combustion pressure sensor in the glow plug; the engine module uses it to control injection for each cylinder. This code concerns cylinder 3. P03AC means the sensor signal stays above its upper limit. GM's European 2.0 CDTI diesel (Saab 9-5, 2010) sets it when the signal is above the threshold for more than 2 s with the engine running, checked once per drive cycle, with the check engine light after two trips; the displayed maximum combustion pressure then reads 10,000 kPa instead of the normal 0–9,000 kPa. Saab names a 5 V reference shorted to positive, an open signal wire or one shorted to positive, and an open ground wire as causes – an unplugged connector is the most common. Without the signal, combustion control for this cylinder is switched off, which is usually barely noticeable.

Likely causes

Symptoms

• Check engine light on (often after two trips)
• Usually barely noticeable – combustion control for the cylinder is switched off
• Possibly rougher running, more noise or slightly higher consumption

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.