OVERVIEW
Genuine VW/Audi coolant control solenoid valve, part number 4H0-121-671-D. This electrically operated valve controls coolant flow in its assigned hose circuit. Correct operation helps the vehicle manage coolant circulation and cabin heating according to the factory system design.
Technical details
- Original part number: 4H0-121-671-D / 4H0121671D.
- Coolant hose valve with electrical connector, two hose connections and mounting tabs, as shown in the original photos.
- Catalog names include coolant solenoid valve, water hose valve and heater control valve.
- Replaces 4H0-121-671-B where the original valve assignment calls for this replacement.
- Supplied as one valve. Hoses, clamps, coolant and mounting hardware are separate.
- This is a coolant flow control valve. Match its exact circuit location and original part number rather than identifying it solely by appearance.
Common reasons to replace
Replace the valve when testing confirms a failure to operate, an electrical fault or leakage from the valve body. Reduced heater output or coolant loss can warrant inspection, but those symptoms also have other causes in the cooling and climate systems.
Factory service information identifies coolant leakage into the electrical connector as an important inspection point. Coolant can travel into the wiring and damage connectors or connected electronics. Inspect for moisture, residue and corrosion; replacing the valve alone will not repair wiring that has already been affected.
Installation and service notes
Let the cooling system cool completely before opening it. Identify the failed valve and record its hose routing, flow markings and connector orientation. Protect the connector from spilled coolant and inspect the surrounding hoses, clamps and mounting points.
Install the replacement in the assigned orientation and follow the vehicle-specific cooling-system filling and bleeding procedure. Use the specified coolant, verify hose security and check for leaks and heater operation after service. Perform the applicable diagnostic checks when a circuit fault was present.
Fitment
| Vehicle | Model years | Engine | Valve assignment |
|---|---|---|---|
| Audi A3 | 2015 | 1.8L turbo gasoline | Front-wheel-drive sedan or Cabriolet; cooling hose solenoid |
| Audi A3 quattro | 2015 | 2.0L turbo gasoline | Engine CNTC; sedan or Cabriolet; cooling hose solenoid |
| Audi Q3 | 2015–2018 | 2.0L turbo gasoline | First-generation front-wheel-drive model; matching water-hose valve |
| Audi Q3 quattro | 2015–2018 | 2.0L turbo gasoline | First-generation quattro model; matching water-hose valve |
| Audi A6 quattro | 2012–2018 | 3.0L supercharged V6 gasoline | Gasoline model; original coolant valve assignment must match |
Confirm the original valve number and coolant hose circuit before ordering.