What it means
A general electrical fault on the cylinder 8 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 8 pressure sensor measures combustion pressure for the engine's closed-loop combustion control. This general circuit code indicates an electrical problem in the sensor, wiring, supply, or ground, so the module may not receive a usable cylinder 8 pressure signal.
Common causes
Most likely first.
- Cylinder 8 pressure sensor failure
- Damaged or corroded sensor connector
- Open or shorted sensor wiring
- Fault in the sensor supply or ground circuit
Symptoms
- Check-engine light
- Rough or uneven engine running
- Misfire or hesitation
- Reduced engine power
How to diagnose it
- Record freeze-frame data and check whether the fault is present now or occurred only under particular engine conditions.
- Inspect the cylinder 8 pressure sensor connector and harness for corrosion, moisture, loose terminals, chafing, or visible damage.
- Compare cylinder 8 live pressure data with other cylinders to see whether the reading is absent, fixed, or erratic.
- Test the cylinder 8 signal, supply, and ground circuits for opens or shorts using the manufacturer's wiring information.
- If the wiring and connections are sound, test the sensor against the manufacturer's specification.
Common fixes
- Clean and secure the cylinder 8 pressure sensor connector or repair damaged terminals.
- Repair an open, shorted, or chafed section of cylinder 8 sensor wiring.
- Restore a faulty sensor supply or ground connection.
- Replace the cylinder 8 pressure sensor if it fails testing with a sound circuit.
Can I keep driving?
With only the check-engine light and normal engine operation, limit driving and arrange diagnosis soon. If the engine runs roughly or loses power, avoid further driving because combustion control may be affected.
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.