P2679: Coolant Degassing Valve Control Circuit Low
What to do
Probably nothing to feel immediately, but worth sorting rather than leaving — this valve vents air out of the cooling system, and trapped air causes hot spots the temperature gauge cannot see.
Ask for the connector itself to be inspected for coolant contamination before the valve is replaced. This part sits in the hottest, wettest part of the cooling system, and a slightly weeping hose joint or seal above it will drip coolant into the plug. Coolant conducts electricity and corrodes terminals, so it produces a genuine electrical fault with nothing wrong with the wiring — and a new valve plugged into a contaminated connector fails the same way. Crusty green or white deposits in the plug are the giveaway.
What this code means
The coolant degassing valve's control circuit reads below its valid range — a short to ground, or a module output that has failed low.
What the valve does and why trapped air matters is set out at P2678.
One cause deserves naming first here, because it is specific to where the part lives and it is not really an electrical fault at all. This valve sits at a high point of the cooling system, in the flow of hot coolant, and its connector sits directly above or beside a joint carrying that coolant under pressure. A weeping hose clip, a seeping seal or a slightly porous plastic housing puts coolant onto that plug, and coolant is conductive and corrosive — it bridges the terminals and then eats them.
The corpus records this pattern elsewhere as coolant leaking into a sensor connector, and it behaves the same way here: the electrical fault is real, the wiring is undamaged, and replacing the valve without finding the seep means the new one's connector corrodes too. Green or white crust in the plug is the tell.
Driveability is normally unaffected in the short term; the consequence is air accumulating over time.
Likely causes
Start here
- Coolant leak into the sensor connector · moderate
- Wiring shorted to ground · moderate
- Corroded or loose connector · easy
- Faulty coolant degassing valve · moderate
Less common
- Control module driver failure · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P2679.