P03E4: Cylinder 8 Combustion Performance

What does P03E4 mean?

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 8. P03E4 means the combustion quality in the cylinder, evaluated from the combustion pressure, is abnormal. No manufacturer document available to us describes the code; a GM patent shows the method: the ratio of measured to motoring pressure is turned into a measure of combustion energy, an inequality index against the neighbouring cylinders in firing order is formed, and a two-sided threshold detects partial combustion, misfire, injector and compression faults. CARB requires engines with a combustion or combustion quality sensor to detect misfire more sharply (5 % in 1,000 revolutions). Typical causes are a coked or leaking injector, compression loss or poor fuel; the engine runs roughly and smokes more.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light on
• Rough running, vibration
• Loss of power, more smoke and consumption

Common causes

• High Injector coked, leaking or delivering the wrong quantity
• Medium Compression loss (valve, rings)
• Medium Partial combustion or misfire (fuel quality, EGR distribution)
• Low Pressure sensor drifting

Likelihood is a general estimate across vehicles; your make and model may differ.