What Does P2678 Mean?
The coolant degassing valve control circuit is open or not functioning. This valve removes air from the cooling system; circuit issues prevent proper valve operation.
Common Causes
35%
Broken or disconnected wiring to degassing valve solenoid
30%
Failed coolant degassing valve solenoid
15%
Blown fuse in degassing valve control circuit
15%
Corroded or damaged connector at valve
5%
Failed ECM driver circuit
Diagnostic Steps
1
Step 1: Locate coolant degassing valve and inspect wiring and connector for damage or corrosion
2
Step 2: Check fuses related to cooling system control circuits
3
Step 3: Disconnect valve solenoid and measure coil resistance; compare to specifications
4
Step 4: Test for voltage supply and ground at valve connector with key on
5
Step 5: Command valve operation with scan tool and verify function; replace valve if no operation
Estimated Repair Cost
$200 - $600
Parts + labor, varies by vehicle and location
The coolant degassing valve control circuit is open or not functioning. This valve removes air from the cooling system; circuit issues prevent proper valve operation.
The most common cause of P2678 (Coolant Degassing Valve Control Circuit/Open) is: Broken or disconnected wiring to degassing valve solenoid
Typical repair costs for P2678 range from $200 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Monitor coolant temperature closely. Air trapped in cooling system may cause overheating if not addressed promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P2678 to identify the root cause.
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Quick Info
Category
Powertrain
System
Cooling System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
