Engine Coolant Temperature Sensor on the 2018-2023 Audi S4: A Complete Guide
Getting a coolant warning on your S4? It might not be what you think—read this before you buy a new sensor.
- Error codes for a coolant sensor on your S4 are often caused by a failing thermostat, not the sensor itself.
- Always have a professional diagnose the issue before buying parts to avoid unnecessary repairs.
- The B9 S4 has multiple, hard-to-reach coolant sensors, making replacement a job for an experienced mechanic.
- If a sensor is confirmed bad, choosing a premium aftermarket or OEM part is a wise investment for this engine.
Is Your Audi S4 Showing a Coolant Warning?
If you own a 2018-2023 Audi S4, you might see a dashboard warning like "Coolant temperature too high" even when the temperature gauge looks normal. You might also notice the engine cooling fans running on full blast for no reason. These are common signs that point to a problem in the cooling system, and the Engine Coolant Temperature (ECT) sensor is often the first part people suspect.
🎬 Watch: 4 common causes for an Audi coolant warning lightA Critical Warning for S4 Owners: Check the Thermostat First
Before you replace any sensors, be aware of Audi's Technical Service Bulletin (TSB) 2058767/8. This document notes that error codes related to the coolant temperature sensor (like P017B and P01E4) are often caused by a faulty thermostat, not a bad sensor. The TSB specifically says that replacing the sensor will not solve this issue. Many owners have fixed their problem by replacing the thermostat, so it's crucial to diagnose the issue correctly to avoid buying parts you don't need.
🎬 See this walkthrough on replacing the S4 thermostat and water pumpChoosing an Aftermarket Engine Coolant Temperature Sensor
If you and your mechanic have confirmed the sensor itself is faulty, you have a choice between an original Audi part (OEM) and an aftermarket one. For a critical component like this on a high-performance engine, quality matters.
- OEM Sensors: These are the same parts Audi uses at the factory. They are guaranteed to fit and work correctly but come at a higher price. One estimate puts the OEM part cost surprisingly high, suggesting it may be part of a larger assembly.
- Premium Aftermarket (e.g., VNE): Brands that are OEM suppliers, like VNE, often offer the same quality part without the dealer markup. These are generally a reliable choice for Audi vehicles.
- Value Aftermarket (e.g., Global Parts): These brands offer a more affordable option. While they are designed to meet original specifications, their long-term durability and accuracy may not match premium brands. For a sensitive system like the S4's, a premium aftermarket or OEM part is often the safer bet.
| Part Type | Estimated Cost |
|---|---|
| New OEM | $70 - $433* |
| New Aftermarket (VNE, Global Parts) | $26.59 - $195.41 |
| Shop Labor | $73 - $150 |
*Note: OEM part cost can vary. One source estimates a high cost of $433, which may include other components. Aftermarket prices are based on available inventory. Labor costs are estimates and vary by shop.
Frequently Asked Questions
Where is the coolant temperature sensor located on my S4?
The 3.0T V6 engine in the B9 S4 has multiple coolant temperature sensors. Forum discussions indicate there are at least four: one at the cylinder head (G62), one downstream of the engine (G82), one at the crankcase (G694), and one at the radiator outlet (G83). 🎬 Watch: Understanding Audi coolant sensor locations and wiring diagrams Their locations are not easily accessible, and identifying the correct one to replace can be difficult, making this a job best left to a mechanic with Audi experience.
Can I replace the sensor myself?
Due to the difficulty in accessing the sensors and the complexity of the cooling system, this is not recommended as a DIY job for most owners. The system must be properly drained, refilled, and bled of air to prevent overheating. Given the high chance the issue could be the thermostat instead of the sensor, professional diagnosis is highly recommended.
Are there any recalls for this part?
No, there are no recalls from the NHTSA for the engine coolant temperature sensor on the 2018-2023 Audi S4.
What happens if I ignore a bad sensor?
Ignoring a faulty ECT sensor can lead to serious problems. The engine may run poorly, get bad fuel economy, and fail emissions tests. Most importantly, if the sensor fails to tell the computer the engine is hot, the cooling fans may not turn on, leading to overheating and potential engine damage.
Helpful Videos
Technical Specifications
The B9 S4 uses multiple 2-pin coolant temperature sensors. The exact part number depends on which of the several sensors has failed.
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Audi S4: