What does it mean?
The module does not only check that the cylinder 2 pressure signal is electrically alive, it also checks that the value makes sense for the conditions the engine is in at that moment. Before the engine starts the sensor should read close to atmospheric pressure, during compression it should rise in a known relationship to crank angle, and during combustion it should peak within a predictable band.
This code is stored when the signal stays inside its electrical limits but fails one of those plausibility checks, so the voltage is valid while the pressure it represents is not. A drifted zero point, a damped or blocked pressure channel and a genuine mechanical change in the cylinder can all cause it. Because the module cannot separate a lying sensor from a sick cylinder on the signal alone, it disables closed loop combustion control for cylinder 2 and turns on the MIL (check engine lamp).
Symptoms
- MIL (check engine lamp) on, sometimes without any dramatic change in how the engine drives
- Idle slightly less smooth and a change in the combustion note the driver may describe as harsher
- Cold starting takes a little longer and produces more smoke than normal
- Mild loss of power and a small but steady increase in fuel consumption
- Additional cylinder balance or combustion performance codes appearing over time
- Occasional unevenness under light load that comes and goes with temperature
Likely causes
- Sensor whose zero point or gain has drifted with age, so the reported pressure no longer matches reality
- Carbon or soot restricting the pressure channel in front of the sensing element and distorting the curve
- Sensor not seated correctly, tightened to the wrong torque or fitted with a damaged sealing washer
- Incorrect sensor variant installed, with an output characteristic the calibration does not expect
- High resistance in the signal, reference or ground circuit shifting the whole reading by a fixed offset
- Genuine mechanical change in cylinder 2 such as low compression or a leaking valve that puts the trace outside the model
- Timing or valve train problem that moves the pressure peak away from the expected crank angle
How to fix it
- Compare the live pressure signals from all cylinders with the ignition on and the engine stopped; every sensor should read close to the same value
- Check the compression and injector correction values for cylinder 2 to confirm whether the cylinder itself is healthy
- Inspect the connector and measure the resistance of the signal, reference and ground circuits back to the module
- Remove the sensor and examine the tip, the pressure channel and the sealing washer for carbon packing and damage
- Verify the part number of the fitted sensor against the specification, since a substituted variant reads with the wrong characteristic
- Perform a compression or leak down test on cylinder 2 if the sensor and its circuit both check out
- Refit or renew the sensor to the correct torque with a new seal, clear the codes and confirm the pressure trace now sits with the other cylinders at idle and under load