What it means
A general electrical fault on the cylinder 4 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 4 combustion pressure sensor measures pressure in that cylinder for the engine's combustion-control system. This code indicates an electrical fault in the sensor circuit, which may involve the sensor, its connector, wiring, power supply, or ground.
Common causes
Most likely first.
- Cylinder 4 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
- Save freeze-frame data and scan for related cylinder 4 sensor or supply-circuit codes.
- Inspect the cylinder 4 pressure sensor connector for corrosion, moisture, loose pins, or damage.
- Trace the cylinder 4 sensor wiring and check for opens, shorts, or chafing near the sensor and along the harness.
- With the wiring diagram, test the sensor supply and ground circuits against the manufacturer's specification.
- If the circuit checks pass, test the cylinder 4 pressure sensor and its signal as specified by the manufacturer.
Common fixes
- Clean and secure the cylinder 4 sensor connector.
- Repair damaged cylinder 4 sensor wiring or corroded terminals.
- Restore a faulty sensor supply or ground connection.
- Replace the cylinder 4 pressure sensor if it fails the manufacturer's test.
Can I keep driving?
A brief drive may be possible if the engine runs normally, but avoid heavy loads if it misfires or loses power. Stop if it runs roughly or stalls, since the system may not be able to control combustion reliably.
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.