What does it mean?
Cylinder 2 is fitted with a combustion pressure sensor that lets the engine control module see the pressure inside the chamber in real time, and on diesel applications it is usually integrated into the glow plug body. The module supplies a five volt reference and a low reference, reads the returning signal and turns it into a pressure curve tied to crank angle, which it uses for injection timing, cylinder balancing and combustion noise control.
This code is a general circuit fault for that sensor: the module has decided the circuit is not working correctly but has not classified the failure as specifically high, low or intermittent. It is typically set when the signal is missing, implausible at key on, or when the self test carried out before the engine starts does not pass. Once the code is active the module stops using cylinder 2 pressure feedback and falls back to a default fueling strategy.
Symptoms
- MIL (check engine lamp) on with a fault stored against the cylinder 2 pressure sensor
- Idle that feels less refined than usual and a coarser combustion sound
- Harder cold starting and increased smoke during the first seconds of running
- Loss of power because the module reverts to fixed fueling for that cylinder
- Higher fuel consumption over a tank than the driver is used to
- Limp mode on some applications, especially if other cylinder pressure faults are present at the same time
Likely causes
- Open, short or high resistance anywhere in the cylinder 2 sensor signal, reference or ground circuit
- Connector at the sensor that is unplugged, cracked, corroded or contaminated with oil from a leaking seal
- Failed sensing element inside the sensor for cylinder 2
- Harness chafed against the cylinder head, a bracket or a heat shield along the sensor branch
- Damaged shared reference feed that also disturbs the sensors on the neighbouring cylinders
- Sensor fitted loosely or with a damaged seal after previous work, so it does not read the chamber correctly
- Module input circuit fault, considered only once the harness and sensor have been measured
How to fix it
- Read the freeze frame and check whether the other cylinders have stored pressure sensor codes, which would point to a shared reference or ground fault
- Inspect the sensor connector for oil, coolant, corrosion, spread terminals and a damaged seal, then follow the harness looking for chafe points
- With the ignition on and the connector unplugged, measure the five volt reference and the low reference on the harness side
- Check continuity of the signal wire from the sensor connector back to the module pin and test it for shorts to ground and to voltage
- Reconnect and observe the live pressure value at key on and while cranking, comparing it with the other cylinders
- Wiggle the harness and connector while watching the live value to expose an unstable connection
- Repair the wiring or renew the sensor as indicated, refit to the correct torque with a new seal, clear the codes and verify the reading through cranking, idle and a road test