What does it mean?
From the pressure trace of cylinder 3 the module works out when combustion started, how quickly heat was released and how much work that cylinder produced relative to the rest of the engine. This code is stored when that combustion quality evaluation falls outside the calibrated window, so the burn is late, slow, incomplete or otherwise different from what is expected at the current operating point.
It is a result code rather than a circuit code: the sensor is delivering credible numbers, but the combustion those numbers describe is not acceptable. Anything that changes the fuel, the air or the compression in that one cylinder can trigger it, so a structured diagnosis matters more than swapping parts. The module compensates as far as its adaptation allows, then turns on the MIL (check engine lamp) and may limit power.
Symptoms
- MIL (check engine lamp) on, usually with balance, contribution or misfire codes for cylinder 3
- Rough idle with audible unevenness in the exhaust beat
- Poor cold starting and visible smoke during the first minute of running
- Clear power loss and slower response when accelerating with a load
- Higher fuel consumption and louder combustion noise on diesel applications
- Vibration at low engine speed and limp mode on some vehicles after repeated events
Likely causes
- Injector on cylinder 3 spraying poorly because of a coked or worn nozzle, a sticking needle or internal leakage
- Injector correction values out of range or coding that does not match the injector actually installed
- Compression loss in that cylinder from worn rings, a leaking or burnt valve, incorrect valve clearance or a failing head gasket
- Faulty glow plug or weak spark energy delaying the start of combustion when the engine is cold
- Intake port heavily fouled with soot and oil, restricting the air charge to that cylinder only
- Low rail pressure, a restricted fuel filter or air in the fuel affecting delivery to that injector
- Pressure sensor drifted far enough to misrepresent the burn without setting a range code
How to fix it
- Read the freeze frame and compare live combustion data across all cylinders so the size and direction of the deviation are clear
- Check the injector correction and balance values and confirm the coding matches the injector fitted to cylinder 3
- Measure rail pressure and its stability, inspect the fuel filter and check the fuel for air or water
- Test the glow plug or the ignition components for that cylinder if the deviation is worst on a cold start
- Inspect the intake port and the exhaust gas recirculation path for heavy soot that would starve the cylinder of air
- Perform a compression or leak down test on cylinder 3 and compare it with the other cylinders before condemning the injector
- Repair the cause found, clear the codes and confirm on a road test that the combustion values for cylinder 3 return to the same band as the rest of the engine