What does it mean?
With a valid pressure trace available, the module measures the peak pressure reached in cylinder 2 during each power stroke and compares it with the value its model predicts for the current speed, load, charge air and injected quantity. This code is stored when the measured peak stays below the calibrated lower limit, so cylinder 2 is producing less pressure than it should. The electrical signal here is inside its normal range, which shifts the diagnosis toward mechanical condition, fuel delivery to that cylinder, or a sensor reading low. A weak cylinder contributes less torque than its neighbours, and the module often records contribution or balance faults alongside this code. The MIL (check engine lamp) comes on and many applications limit power until the fault is corrected.
Symptoms
- MIL (check engine lamp) on, usually with contribution, balance or misfire codes for cylinder 2
- Rough idle with a repeating beat that the driver can both hear and feel
- Poor cold starting and grey or white smoke during the first minute of running
- Clear power loss and slow response when accelerating under load
- Higher fuel consumption as the module compensates for the weak cylinder
- Vibration through the body at low engine speed and limp mode on some applications
Likely causes
- Compression loss in cylinder 2 from worn or stuck rings, a burnt or poorly seating valve, or a head gasket starting to leak
- Injector for cylinder 2 under delivering because of a blocked nozzle, a worn needle or coding that does not match the fitted part
- Fuel supply shortfall to that injector, including low rail pressure, a restricted filter or air in the system
- Carbon or soot packed into the sensor pressure channel, damping the measured peak
- Sensor that has drifted low with age and now under reports true chamber pressure
- Valve clearance out of specification or a worn camshaft lobe reducing effective compression on that cylinder
- Intake port heavily fouled with soot, restricting the air charge reaching cylinder 2
How to fix it
- Read the freeze frame and compare live pressure traces of all cylinders at the same operating point so the size of the shortfall is clear
- Inspect the sensor connector and harness, then compare the cylinder 2 signal with its neighbours at idle and at steady load
- Check rail pressure and the injector correction values for cylinder 2, and confirm the injector coding matches the installed part
- Perform a compression or leak down test on cylinder 2 and compare the results directly with the other cylinders
- If the leak down points at the valve train, check valve clearance, cam lobe wear and valve seating before suspecting the rings
- When the mechanical tests are normal, remove the sensor and inspect its pressure channel for carbon, replacing the sensor if it reads low against a healthy cylinder
- Repair the cause found, clear the codes and confirm on a road test that the cylinder 2 peak pressure matches the rest of the engine