P2678Coolant Degassing Valve Control Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- In a sealed cooling system, air and vapour bubbles are carried through a thin vent line into the expansion tank, where they separate from the liquid; a bubble-free circuit avoids local hot spots, as cooling suppliers such as MAHLE point out. Some engines put an electrically switched valve in this degassing path so the controller can close it, for example to speed up warm-up. P2678 reports an open or unspecified fault in the drive circuit of that valve. No manufacturer documents P2678 or its valve publicly, so neither the purpose nor any threshold can be named. CARB requires electrical checks of controlled cooling system components. If the valve fails in the wrong state, warm-up can lengthen or venting may be impaired.
- What you may notice
- Check engine light or stored code
- Longer warm-up or slow heater output
- Gurgling or air in the cooling system
- Likely causes
- LikelyUnplugged connector or broken wire to the degassing valve
- PossibleOpen solenoid coil in the degassing valve
- RareFaulty driver in the control module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.