P2679: Coolant Degassing Valve Control Circuit Low

P2679 indicates that the control line of the switched valve in the coolant vent path to the expansion tank reads too low. Usually the wire is grounded somewhere, or the solenoid has shorted turns; with a low-side driver the valve may then stay energised regardless of the command. The engine controller compares the line voltage with the state it set. Dodge lists P2679 among the fault codes that the reprogrammed engine controller of the 2004–2006 Sprinter can newly store under emissions recall T21, but the recall text gives no description of the circuit. Otherwise no maker explains P2679 publicly. CARB requires such circuit checks for controlled cooling components. A valve held in one state can slow warm-up or hinder venting.

Symptoms

• Check engine light or stored code
• Slow warm-up
• Coolant level fluctuations in the expansion tank

Most likely causes

• Control wire shorted to ground
• Shorted turns in the degassing valve solenoid
• Coolant or water leaking into the valve connector

What to check, in order

Start with the simplest. You can tick off each step.

1. With the engine cold, check the coolant level; never do this when the system is hot
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Check the actual temperature in live data
4. Make sure the fan comes on when it should
5. Check the thermostat and connector
6. Measure the sensor and replace it if its readings do not make sense

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P2679 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 6: Control modules and outputs
• 79: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2679?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P2679?

The most common causes are: control wire shorted to ground; shorted turns in the degassing valve solenoid; coolant or water leaking into the valve connector.

Related codes

• P2678Coolant Degassing Valve Control Circuit/Open
• P2680Coolant Degassing Valve Control Circuit High

Sources

• law.cornell.edu: 13 CCR 1968.2
• mahle-aftermarket.com: mah kompaktwissen ec fahrzeugkuehlung de screen
• static.nhtsa.gov: MC 10190682 9999

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.