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I'm crossing my fingers that someone here has some insight into this or can offer some advice.

Even after having the air conditioning system regassed and tested for leaks, my 2015 RS5 still won't turn on or remain on.


This is the error code I'm receiving:
00256 - G395 Air Conditioning Pressure/Temperature Sensor
The absolute pressure was more than 1.4 bar at 0 revolutions per minute, breaching the lower limit.

Looking at the error code online, the most prevalent suggestion is that the air conditioning pressure/temperature sensor (G395), which is situated near the radiator and can be seen through the grille, is failing. I have located the part number to be 4H0 959 126.

It seems like a bit much for a sensor, but TPS has quoted £108.50. Additionally, I came across the identical component on eBay, offered by sasAuto, for approximately £40. They assert that it is an authentic OEM part.

Here are my enquiries:

I was wondering whether anyone else had encountered the same error code and symptoms: was the G395 pressure/temperature sensor replaced to fix the problem, or was something else ultimately to blame?
Does anyone have experience with sasAuto's OEM parts and can attest to their reliability and authenticity?

Before I begin changing parts, I would greatly appreciate any advise, recommendations, or comments.

I am grateful in advance.

A communications problem that occurred every once in a while forced me to replace mine a number of years ago. I believe the sensor and O ring seal were purchased from Audi, and I don't remember paying that much for them. Find out how much a Mahle sensor costs by checking autodoc.
I apologise, but I am unable to resolve the "lower limit" issue.

I appreciate the tagging. There's a classic case of "is the messenger broken, or is the message true?" at work here.

A refrigerant pressure reading from the G395 sensor falls below the minimum threshold needed to properly operate the air conditioner compressor, causing the climate control module to encounter the "Lower limit exceeded" issue. The A/C button won't stay on because the system is refusing to engage as a precautionary step to prevent damage. There are two main possibilities here: either the system pressure is actually too low (because a leak was overlooked during the servicing, for example) or the G395 sensor is malfunctioning and giving an inaccurate reading.


A broken sensor is a typical and reasonable suspect, since the system was just regassed. Telling the ECU there's an issue when none exists is like crying wolf in electronics. In most cases, the solution is to replace the sensor.

Thank you for the information. I was ready to purchase the sensor from TPS after feeling confident about the failed one. However, when I started researching how to install it, I came across an eBay seller named sasAuto advertising the sensor for less than half price. I started to wonder if I was getting the right item.

I've never had any problems with my RS since I bought it in 2017. I've only replaced the battery and the usual servicing parts. I wouldn't normally consider non-OEM parts, but I'm not sure that the part from sasAuto is OEM and costs £40 instead of £100+. If it is, I'm surprised by how expensive TPS and Audi are.Aside from the one from EFI, which is around £121 (JohnS4), there are numerous other brands of sensors ranging in price from around £20 to over £50, and the Mahle sensor from Autodoc is around £31.

Just a friendly reminder: in order to access the sensor without taking the front grille off, I'll need a 3" deep 1/2"sq 24mm socket.

At some point, every car owner will have to deal with the million-dollar (or, more accurately, the seventy-pound) question. Oh, how delightful it is to enter the realm of car parts pricing, where the label may hold more value than the actual part. What you're seeing as a pricing discrepancy is really just a result of the difference between OE and OEM. With an Audi label and a price tag that reflects the dealer's supply chain and warranty, this TPS item is original equipment manufacturer (OE). You're not only getting the part, but also the assurance that comes with the four-ring emblem.

The original equipment manufacturer (OEM) is probably a business like Mahle; they make the sensor for VAG, and then Audi puts it in a package. Without the Audi markup, Mahle sells the identical sensor in its own package. You will most likely see this on Autodoc. The eBay vendor may be selling a genuine OEM part at a low price, but the site is also rife with deceptive knockoffs. You may get OE quality without the OE price with a trustworthy OEM brand like Mahle from a well-known provider, which is perfect if you're looking for reliability. It's the identical section; the pricey autograph is absent.

With the top cover trim gone, I was able to access just enough space to utilise an adjustable wrench. As evidence, I could see a couple of scraped knuckles. Switching out the light bulbs is such a pain in the neck, but this is a breeze in comparison.

You should be aware that a small amount of AC refrigerant will be released when you loosen the sensor. To avoid this loss, unscrew it as soon as possible after loosening it. The same principle applies when installing the new sensor; behind it, there is a self-sealing Schrader valve.

Additionally, before you tighten the new sensor, "collect" as much system oil as you can from the old O-ring seal with your finger and apply it to the new one. This will assist prevent surface damage to the new seal.

The regassing company might have my business again. Plus, after they finish their job, they should double-check that the system is functioning properly.

It seems like the OP recently acquired a multi-branch facility, also known as a 'fast fit' facility, to perform AC recharges more efficiently. According to the law, they are required to draw a hoover and wait (or use their fully automated AC machine to do so) before refilling the system with AC refrigerant. If the system still doesn't work, it would be assumed to be a system failure, and the AC recharge facility wouldn't have any information to assist them with this.

It may sound ridiculous, but at least in the UK there are plenty of "fast fit" companies that can do this work. The idea is that the car just needed its air conditioning system recharged, so everything is OK if that's the case. If not, then someone knowledgeable can start fixing it.