Genuine OEM 4H0121671D - HVAC Heater Control Valve Solenoid

Product Overview

The Genuine OEM 4H0121671D is an HVAC heater control valve solenoid engineered to regulate coolant flow through the heater core in Audi vehicles. This OEM-specification component fits a broad range of Audi models from 2011 onward, including the A3, A4, A5, A6, A7, A8, Q3, Q5, Q7, Q8, S3, S6, S7, S8, RS6, RS7, SQ7, SQ8, and allroad across multiple chassis platforms (D2, B8, C7, C8, 4L, 8R, 8V, 8U, B9, 4M, and others). When the solenoid fails, the heating system cannot properly modulate coolant temperature, resulting in poor cabin warmth or complete loss of heat. As a Genuine OEM part, this solenoid is factory-approved and carries the same warranty assurance as parts supplied directly to Audi dealerships.

Symptoms of a Failing HVAC Heater Control Valve Solenoid

• No heat or insufficient warmth from the cabin vents even when the climate control is set to maximum temperature
• Heat output that is inconsistent or intermittent, working only occasionally
• Hissing or gurgling sounds from the heater core or dashboard area when the heating system operates
• Coolant leaks visible beneath the vehicle or inside the cabin near the firewall
• Check Engine light or climate control fault codes stored in the vehicle's diagnostic memory

Cross Reference Numbers

This Genuine OEM 4H0121671D is equivalent to or replaces the following part numbers: 4H0121671B, 4H0-121-671-D, 4H0121671D.

Vehicle Compatibility

This part fits the popular models below. For Fitment Confidence, please use the vehicle selector tool above to verify exact compatibility for your vehicle.

• Audi A3 2.0 L4 Gas (8V): 2015–2020
• Audi A4 2.0 L4 Gas (B8, B9): 2017–2020
• Audi A4 allroad 2.0 L4 Gas (B9): 2018–2019
• Audi A5 2.0 L4 Gas (B9): 2018
• Audi A5 Sportback 2.0 L4 Gas (B9): 2019
• Audi A6 2.0 L4 Gas (C7, B9): 2012–2018
• Audi A6 3.0 V6 Gas (C7): 2012–2018
• Audi A7 Quattro 3.0 V6 Gas (C7): 2015–2016
• Audi A8 4.2 V8 Gas (D2): 2011–2012
• Audi A8 3.0 V6 Gas (D4): 2013
• Audi A8 4.0 V8 Gas (D4): 2014
• Audi A8 Quattro 3.0 V6 MHEV (D5): 2021
• Audi A8 Quattro 4.0 V8 MHEV (D5): 2021
• Audi A8 Quattro L W12 6.3 Gas (D4): 2014–2015
• Audi Q3 2.0 L4 Gas (8U, F3): 2015–2018
• Audi Q5 2.0 L4 Gas (8R, FY): 2013–2019
• Audi Q5 Hybrid 2.0 L4 FHEV (8R): 2015
• Audi Q7 3.0 V6 Gas (4L, 4M): 2013–2019
• Audi Q7 3.0 V6 MHEV (4M): 2020–2021
• Audi Q7 3.0 V6 TDI Diesel (4L): 2013
• Audi Q8 3.0 V6 MHEV (4M): 2019–2021
• Audi RS6 Avant 4.0 V8 MHEV (C8): 2023
• Audi RS7 4.0 V8 Gas (C7, C8): 2014–2017
• Audi S3 2.0 L4 Gas (8V): 2017–2020
• Audi S6 4.0 V8 Gas (C7): 2016
• Audi S7 4.0 V8 Gas (C7): 2016–2017
• Audi S8 4.0 V8 Gas (D4, D5): 2013–2023
• Audi SQ7 4.0 V8 MHEV (4M): 2021–2022
• Audi SQ8 4.0 V8 MHEV (4M): 2020–2022
• Audi TTS Quattro 2.0 L4 Gas (8J): 2018
• Audi allroad 2.0 L4 Gas (B9): 2016–2018

This may also fit other applications. Please use the vehicle selector tool to verify fitment.

Often Replaced Together

For a complete climate control system service, many owners replace the following at the same time:

• Heater hoses and clamps (to prevent coolant leaks and ensure proper flow)
• Cabin air filter (to maintain air quality and system efficiency)
• Coolant (fresh fluid improves heat transfer and prevents corrosion)
• Thermostat and housing assembly (worn thermostats reduce heating performance)

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Frequently Asked Questions

How do I know if my Audi A4, A6, or Q5 needs a new heater control valve solenoid?

The most common sign is a complete loss of cabin heat or heat that only works intermittently. If you turn the climate control dial to maximum temperature and feel little to no warm air from the vents, the solenoid may be stuck in a closed position, preventing coolant from reaching the heater core. You may also notice hissing or gurgling sounds from inside the dashboard. If the fault persists after the engine has fully warmed up, the solenoid is the likely culprit.

What is the difference between the 4H0121671D and 4H0121671B part numbers?

Both are genuine OEM solenoids for the same heating system application. The 4H0121671B is an earlier version that was superseded by the 4H0121671D. The newer D-suffix part may include minor internal refinements or material updates. Either will function identically in your vehicle, but the D version is the current factory specification.

Can I replace this solenoid myself, or do I need a professional?

Replacing the heater control valve solenoid typically requires access to the engine bay and removal of some climate control ducting or intake manifold components. The job is moderately complex and involves draining or isolating the coolant system to avoid spills. Most DIY enthusiasts with intermediate mechanical skills and a torque wrench can perform the replacement, but professional installation is recommended if you are unfamiliar with coolant system work. Consult your Audi service manual for exact removal steps and torque specifications for your specific model year.

Will replacing the solenoid fix my heating problem, or could something else be wrong?

A faulty solenoid is one of the most common causes of heating loss, but other issues can produce similar symptoms. A clogged heater core, low coolant level, a stuck thermostat, or a failed blower motor can all reduce or eliminate heat output. If the solenoid replacement does not restore full heat, have the coolant level checked, the heater hoses inspected for blockages, and the thermostat tested. A professional diagnostic scan can also reveal whether climate control fault codes point to the solenoid or another component.

Is this part covered under any warranty?

As a Genuine OEM part purchased from eEuroparts.com, this solenoid is backed by our fitment guarantee and the manufacturer's standard warranty. Audi dealerships typically warrant OEM climate control components for 12 months or the balance of the vehicle's factory warranty, whichever is longer. We recommend retaining your receipt and checking your vehicle's warranty status with your local Audi dealer for specific coverage details.

How long does a heater control valve solenoid typically last?

Under normal conditions, a properly functioning solenoid can last the life of the vehicle. However, exposure to heat cycles, coolant contamination, and electrical stress can shorten its lifespan. Most owners experience solenoid failure between 80,000 and 150,000 miles, though some vehicles go much longer without issues. Regular coolant flushes and maintaining proper coolant levels help extend solenoid life by reducing corrosion and internal wear.

Order Genuine OEM 4H0121671D today. In-stock orders ship same or next business day from our U.S. warehouse, and our fitment team is one call away if you need help confirming the right part for your Audi.

Note: All information on this page and in the FAQ is for general reference only. Verify fitment and consult a professional as needed. eEuroparts.com is not responsible for incorrect part selection or installation.