Audi S5 (2008-2018) Engine Coolant Temperature Sensor: A Complete Guide
Understanding the signs of a failing coolant temperature sensor in your S5 and how to choose the right replacement part.
- A failing ECT sensor in an S5 can cause a Check Engine Light (P0117, P0118), poor fuel economy, rough idle, and overheating.
- For Audi electronics, choosing an OEM or OE-supplier brand like Hella, Delphi, or Vemo is strongly recommended for accuracy and reliability.
- The sensor location varies between the 4.2L V8 and 3.0T V6 engines but is typically on the rear of the engine and can be difficult to access.
- Always replace the O-ring and retaining clip with the sensor to prevent coolant leaks.
Symptoms of a Failing ECT Sensor in an Audi S5
A bad coolant temperature sensor can cause a range of problems, from minor annoyances to issues that could lead to engine damage. Because the sensor's reading affects so many systems, the symptoms can sometimes be confusing.
- Check Engine Light: This is often the first sign. Common trouble codes include P0117 (Circuit Low) and P0118 🎬 Watch a diagnostic guide for the P0117 fault code. (Circuit High), which point to a problem with the sensor or its wiring.
- Inaccurate Temperature Gauge: The gauge on your dashboard might read extremely high right after a cold start, or it may not move at all.
- Engine Overheating: If the sensor fails to tell the ECM that the engine is hot, the cooling fans may not turn on, leading to overheating.
- Poor Fuel Economy: An incorrect reading can make the ECM provide a rich fuel mixture (too much fuel), which wastes gas.
- Rough Idle or Misfires: The wrong fuel mixture and ignition timing can cause the engine to run poorly, especially when idling.
- Black Smoke from Exhaust: This is a sign of a very rich fuel mixture, where unburned fuel is exiting through the exhaust.
Generation and Engine Differences
The 2008-2018 S5 was built with different engines, which affects the location and part number of the ECT sensor. The B8 models (2008-2012) have a 4.2L V8, while the B8.5 models (2013-2017) use a 3.0L supercharged V6. The B9 (2018+) uses a 3.0L turbocharged V6. Always confirm the correct part for your specific engine before purchasing.
Choosing the Right Aftermarket Sensor
When replacing the ECT sensor, you have a choice between OEM (Original Equipment Manufacturer) and various aftermarket brands. For a critical electronic part like this on an Audi, quality matters.
Tier 1: OEM & OE Supplier Brands
These brands are either the original supplier to Audi or are known for equivalent quality. They are the most reliable choice for fit, accuracy, and longevity. Forum users and mechanics often recommend sticking to these brands for electronic components on German vehicles to avoid issues.
- Hella: A well-respected German company that is often an OE supplier.
- Delphi: Another top-tier OE supplier with a strong reputation for electronic components.
- Vemo: A quality brand that often provides parts to the OEM market.
Tier 2: Reputable Aftermarket Brands
These brands offer a good balance of quality and value. They are generally reliable and a solid choice if an OE supplier part is not available or is outside your budget.
- Beck Arnley: Known for sourcing parts from various OE-quality manufacturers and repackaging them.
- NGK/NTK: While famous for spark plugs, their sensor line is also well-regarded.
- Standard Ignition (SMP): A long-standing brand with a wide range of reliable electronic parts.
Tier 3: Budget-Friendly Options
These brands offer the lowest price point. While tempting, be aware that the quality, accuracy, and lifespan may not match higher-tier brands. Using a lower-quality sensor could lead to incorrect readings, poor performance, or premature failure, requiring you to do the job again.
- Four Seasons
- Global Parts
- True Tech
Pro Tip: When replacing the sensor, it's also a good idea to replace the small O-ring seal and the retaining clip. These are inexpensive and ensure a leak-free installation. Some aftermarket sensors include these in the box.
Known Issues, TSBs, and Recalls
Searches for the 2008-2018 Audi S5 did not reveal any specific recalls or Technical Service Bulletins (TSBs) directly for the Engine Coolant Temperature Sensor itself. However, there have been recalls related to the electric coolant pump on some Audi models with 2.0L TFSI engines, which are not the engines used in the S5 of this period. Some TSBs mention coolant temperature sensor codes (like P017B00) as a symptom of a failing thermostat, not necessarily the sensor itself. If you have multiple cooling system codes, it's wise to diagnose the entire system.
Cost of Replacing an Audi S5 ECT Sensor
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Sensor | $13 - $44 |
| New OEM Sensor | $30 - $50 |
| Shop Labor | $73 - $107 |
| Total Professional Replacement | $86 - $151 (Aftermarket) / $103 - $157 (OEM) |
Frequently Asked Questions
How many coolant temperature sensors does my S5 have?
Some Audi engines use multiple coolant temperature sensors. For example, one sensor might be at the coolant outlet on the engine (G62), while another might be at the radiator outlet. It is essential to diagnose which sensor has failed, though the main engine sensor (G62) is the most common one to cause performance issues.
Where is the ECT sensor located on the S5?
The location varies by engine. On the 4.2L V8 and 3.0L V6 engines, the main G62 sensor is typically located on the back of the engine, near the firewall, often in 🎬 See the exact sensor location and wiring on B8 models. a plastic coolant flange. It can be difficult to access. On the 3.0T, it is often replaced during larger jobs like a thermostat or water pump replacement.
🎬 Learn how to access the sensor during a thermostat job.Is an OEM sensor really better for my Audi?
For critical electronic sensors on German cars, using an OEM or OE-supplier part (like Hella, Delphi, Vemo) is highly recommended. While more expensive than budget options, they provide the most reliable and accurate readings, preventing frustrating performance issues and the need for a premature replacement.
What happens if I don't replace a bad ECT sensor?
Ignoring a faulty ECT sensor can lead to persistent poor fuel economy, failed emissions tests, rough engine performance, and potentially severe engine damage from overheating if the cooling fans don't activate correctly.
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Technical Specifications
OEM Part Numbers: 079919523J 06A919501A 059919501A 079919525M
Typically a 2-pin or 4-pin thermistor sensor that changes resistance based on coolant temperature. Comes with a rubber O-ring for sealing.
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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 S5: