P03AA Cylinder 3 Pressure Sensor Circuit Range/Performance

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. P03AA means the sensor signal is electrically fine but does not fit the expected value. No manufacturer document available to us describes the code; a GM patent shows how such a check works: in overrun the measured peak pressure is compared with a compression pressure calculated from manifold pressure and compression ratio, and the pressure values are also compared with limits and with crankshaft speed fluctuation. GM's European diesel in the Saab 9-5 uses the peak pressure in overrun anyway to find top dead centre. Typical causes are sensor drift from combustion deposits or a glow plug that leaks or is wrongly torqued. CARB requires a two-sided plausibility check of input sensors where feasible.

Likely causes

Symptoms

• Check engine light on
• Combustion control for the cylinder off – slightly rough running, more noise
• Possibly more smoke or consumption

Repair estimate

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

Parts involved

Related codes

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