P03C9 Cylinder 6 Pressure Sensor Circuit Low

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 6. P03C9 means the sensor signal stays below its lower limit – typically an open or grounded 5 V reference or a signal wire shorted to ground. The only manufacturer we found using this code family, GM's European 2.0 CDTI four-cylinder diesel (Saab 9-5, 2010), uses it for cylinders 1 to 4: signal below the threshold for more than 2 s with the engine running, check engine light after two trips, displayed pressure 0 kPa. For cylinder 6, which only engines with at least 6 cylinders have, no manufacturer document available to us uses the code; the description follows that logic and CARB. Without the signal, combustion control for this cylinder is switched off.

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