What does it mean?
For cylinder 3 the module predicts a peak combustion pressure from engine speed, injected quantity, boost, intake air temperature and injection timing, and then checks that prediction against what the in cylinder sensor actually measures. This code is stored when the measured peak climbs above the calibrated upper limit, meaning combustion in that cylinder is more energetic or begins earlier than the model permits.
Pressure above design intent loads the piston, the rod bearing and the head gasket, so the strategy handles this as a protection issue and reacts without delay. The circuit is normally electrically sound here, which points the investigation at fueling, charge air, timing and mechanical condition. Most applications turn on the MIL (check engine lamp) and cut fuel or boost until the cause is removed.
Symptoms
- MIL (check engine lamp) on, sometimes with boost pressure or injector correction codes as well
- Hard metallic knock or a sharp combustion rattle under load that is clearly audible in the cabin
- Rough running under acceleration while the idle may still feel acceptable
- Power reduction or limp mode that appears as soon as load is applied
- Higher exhaust temperature and a hot smell after a long climb
- More vibration through the pedals when pulling in a high gear
Likely causes
- Injector on cylinder 3 over delivering because of a leaking nozzle, a stuck needle or coding that does not match the fitted injector
- Injection or ignition timing advanced too far for the load and fuel, producing an early and steep pressure rise
- Boost above target from a stuck wastegate, a seized variable geometry mechanism or a failed boost control actuator
- Heavy carbon on the piston crown and in the chamber raising the effective compression ratio
- Exhaust gas recirculation blocked or stuck closed, removing the charge dilution that normally limits peak pressure
- Sensor that has drifted high and over reports the real chamber pressure
- Wrong fuel grade or contaminated fuel igniting earlier than the calibration expects
How to fix it
- Read the freeze frame and note the boost, injected quantity and timing values recorded when the code set
- Compare live peak pressures across all cylinders at the same operating point to establish whether cylinder 3 is genuinely different
- Check actual boost against the commanded value and inspect the wastegate or variable geometry mechanism for sticking
- Review the injector correction values for cylinder 3, confirm the coding and have the injector tested for leakage if the corrections are abnormal
- Verify injection or ignition timing and look for sensor correlation faults that could advance it
- Inspect the exhaust gas recirculation valve and cooler for a blocked or stuck closed condition
- If everything else is normal, compare the sensor with a known good unit and check the chamber for carbon build up before returning the vehicle