What it means
A general electrical fault on the cylinder 3 combustion pressure sensor — used on engines with closed-loop combustion control (e.g. some Volvo and BMW direct-injection diesels) to measure cylinder pressure directly via a sensor at the glow plug or injector position.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The cylinder 3 pressure sensor measures combustion pressure so the engine control module can monitor that cylinder's operation. This code indicates an electrical fault in the cylinder 3 sensor circuit, which can involve the sensor, wiring, connector, power supply, or ground.
Common causes
Most likely first.
- Cylinder 3 pressure sensor failure
- Damaged or corroded sensor connector
- Open or short in sensor wiring
- Fault in the sensor power or ground circuit
Symptoms
- Check engine light on
- Rough running or misfire
- Reduced engine power
- Hard starting
How to diagnose it
- Record freeze-frame data and check live cylinder 3 pressure data for a missing, fixed, or implausible reading.
- Inspect the cylinder 3 pressure sensor connector for corrosion, moisture, loose fit, damaged seals, or pushed-back pins.
- Trace the cylinder 3 sensor harness for chafing, pinching, or breaks, and inspect its routing near hot or moving parts.
- Check the sensor supply and ground connections against the manufacturer's specification.
- Test the cylinder 3 signal and wiring for an open or short, then assess the sensor if the circuit checks pass.
Common fixes
- Clean and dry the cylinder 3 sensor connector and restore its seal.
- Repair loose or corroded connector terminals.
- Repair an open or short in the cylinder 3 sensor wiring or its power and ground circuits.
- Replace the cylinder 3 pressure sensor if its circuit is sound but it does not provide a valid signal.
Can I keep driving?
Drive gently and avoid heavy loads if the engine is rough or down on power; the module may not be able to monitor cylinder 3 combustion correctly. Stop if it misfires severely or stalls, and arrange diagnosis soon.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.