P2679: Coolant Degassing Valve Control Circuit Low

What it means

The coolant degassing valve control circuit voltage is below its expected range.

At a glance

• Usually lights the check-engine light

How it works

The controller operates the coolant degassing valve to help manage coolant flow and remove trapped air. P2679 sets when voltage in the valve control circuit is below its expected range, often because the control wire is grounded, the coil is shorted, or a connector has poor contact.

Common causes

Most likely first.

1. Control wire shorted to ground
2. Internal short in solenoid coil
3. Connector pins corroded - high contact resistance

Symptoms

• Check-engine light
• Engine may take longer to reach operating temperature

How to diagnose it

1. Read freeze-frame data and check for related cooling-system or electrical codes that may explain the low circuit reading.
2. Inspect the degassing valve connector and harness for chafing to ground, coolant or water intrusion, corroded pins, and loose terminals.
3. Monitor the circuit while gently moving the harness near the valve connector to see whether the low reading changes.
4. Disconnect the valve and check whether the low condition remains on the vehicle-side control wire, separating a harness fault from a shorted coil.
5. Test the valve coil and circuit against the manufacturer's specification, including the wiring's continuity to ground and connector contact quality.

Common fixes

• Repair a control wire shorted to ground or damaged by chafing.
• Clean or replace corroded, loose, or damaged connector terminals.
• Replace a coolant degassing valve with an internally shorted coil.
• Repair a controller circuit fault only after the valve and wiring are verified.

Can I keep driving?

Monitor coolant temperature closely and avoid long trips until the valve circuit is repaired. Stop if the engine overheats, because cooling problems can quickly cause engine damage.