P2679 — Coolant Degassing Valve Control Circuit Low #

The description of this diagnostic trouble code (DTC) may vary depending on the vehicle manufacturer.

• Coolant Degassing Valve Control Circuit Low (General)
• Coolant System Air Bleed Valve Control Circuit Low (Ford)
• Engine Coolant Bleed Valve Circuit Low (GM/Chevrolet)
• Low Signal – Coolant Degassing Valve (BMW)

Summary of DTC P2679 #

The P2679 code indicates that your vehicle’s Powertrain Control Module (PCM) — the onboard computer managing engine and transmission — has detected a low voltage condition in the control circuit for the coolant degassing valve. This valve, sometimes called an air bleed valve, is responsible for releasing trapped air from the engine’s coolant system to prevent overheating and ensure efficient operation. When the PCM expects a certain electrical signal from this circuit and receives less than expected, it sets this code. A persistent P2679 code, if ignored, can lead to cooling system inefficiency, potential overheating, and increased engine wear. While this code may seem minor at first glance, addressing it promptly helps protect your engine’s long-term health.

Common Symptoms for DTC P2679 #

If this DTC is present, your vehicle may display one or several noticeable symptoms. Some drivers may not detect any issue initially, as early warning signs are sometimes subtle. However, ignoring these symptoms can lead to more severe problems. Common symptoms include:

• Illuminated Check Engine Light (CEL)
• Repeated or intermittent engine overheating
• Erratic or fluctuating engine temperature gauge
• Reduced heating performance from the cabin heater
• Unusual gurgling or bubbling noises from the coolant reservoir
• Possible cooling fan running more frequently than normal

Most Likely Causes for Code P2679 #

The P2679 code is usually triggered by electrical or mechanical issues within the coolant degassing valve circuit. Understanding the most common causes can save valuable time during diagnosis. Here they are, in order of frequency:

1. Faulty coolant degassing (air bleed) valve — the internal solenoid or actuator has failed.
2. Open or shorted wiring harness in the degassing valve control circuit — damaged, frayed, or corroded wires.
3. Poor electrical connection at the valve or PCM connector — loose or corroded pins.
4. Failed PCM (rare) — the computer is unable to provide or sense the correct signal.
5. Blown fuse or relay in the coolant valve control circuit.

Step-by-Step Diagnostic for P2679 #

A methodical approach is essential to correctly identify the root cause of DTC P2679. Here’s a step-by-step process any technician (or advanced DIYer) should follow:

• Scan for additional DTCs — Check for related codes that might indicate broader electrical or cooling system issues.
• Perform a visual inspection — Look for obvious damage to wiring, connectors, and the degassing valve itself.
• Check electrical connections — Unplug the valve and PCM connectors; inspect for bent, corroded, or loose pins.
• Test circuit voltage — Using a digital multimeter, verify that the degassing valve receives the correct voltage and ground as specified by the manufacturer.
• Test the valve actuator/solenoid — Measure resistance; compare to OEM specs. Out-of-range values indicate a faulty valve.
• Check fuse/relay — Confirm that the relevant fuse and relay are intact and functional.
• Test at PCM — If all else checks out, verify the PCM’s output and input for the circuit.
• Clear the code and test drive — After repairs, clear the code and drive the vehicle to ensure the issue is resolved.

Possible Repairs for P2679 #

Once the root cause is identified, the appropriate repair can be made. Repairs are directly linked to the causes found during diagnostics, and may include:

• Replacing a faulty coolant degassing/air bleed valve
• Repairing or replacing damaged wiring or connectors
• Cleaning and securing corroded connections
• Replacing a blown fuse or faulty relay
• In rare cases, replacing or reprogramming the PCM

Is It Safe to Drive with Code P2679? #

Limited/Not Recommended: While some vehicles with P2679 may still operate seemingly fine, continuing to drive can risk engine overheating if air pockets in the coolant system are not properly vented. Overheating is a silent killer for engines and can lead to expensive repairs (warped cylinder heads, blown gaskets). It’s best to address this code as soon as possible and avoid long trips or heavy traffic until repairs are made.

Vehicles Most Commonly Affected by P2679 #

Although any modern vehicle with an electronically controlled coolant degassing valve can experience this issue, it is more frequently seen in certain makes and models that use advanced cooling management systems. Vehicles commonly reported with this code include:

• Ford (Fusion, Escape, Focus, Mondeo)
• Chevrolet (Malibu, Cruze, Equinox)
• BMW (3 Series, 5 Series)
• GM (various models with electric coolant valves)
• Jaguar/Land Rover (recent models with advanced thermal management)

Common Mistakes & Best Practices with P2679 #

Misdiagnosis is surprisingly common with this code, especially if the technician skips critical steps or overlooks simple issues. To avoid headaches and wasted time, keep these in mind:

• Don’t replace the degassing valve without first checking wiring and connections.
• Avoid clearing the code without addressing the root cause — the issue will return.
• Always use OEM parts for replacement; aftermarket valves may not function correctly.
• Remember that coolant system air pockets can cause similar symptoms but won’t set this electrical code directly.
• Document all diagnostic steps and repairs for future reference.

Express FAQ — P2679 #

Q1: Will simply topping up coolant fix a P2679 code?
A1: No. This code is electrical in nature and relates to the degassing valve’s control circuit, not just coolant level. Topping up coolant won’t resolve the underlying issue.

Q2: Can a faulty thermostat trigger P2679?
A2: Unlikely. The thermostat is separate from the degassing valve circuit. However, if cooling system issues are ignored, multiple codes could eventually be set.

A methodical approach will save you time, money, and potential engine headaches. If in doubt, consult a qualified technician or your OEM’s repair literature.