P03A9 Cylinder 3 Pressure Sensor Circuit

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. P03A9 is the general circuit code for this pressure sensor, meant for modules that do not separate open circuits and shorts into low and high. The only manufacturer we found using this code family – GM's European 2.0 CDTI diesel, documented in Saab 9-5 workshop information – splits the faults into low and high (P03AB, P03AC) and does not use P03A9; VW's US 2.0 TDI engines with pressure-sensing glow plugs report such faults with their own codes (P13CE ff). The description therefore follows CARB's requirement to monitor input sensors for circuit faults. The sensor has three wires (5 V reference, ground, signal); without it the module drops combustion control for that cylinder.

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, borgwarner.com, patents.google.com, saabwisonline.com.