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2004 S500 4Matic
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228 Posts
Discussion Starter #1
Hi. I'm finding that I have to reset my TPMS system every time I start my car. I didn't have to do this originally but it started happening about a month ago. I plan to take the car to my dealer, but I'd like to avoid a visit if there is a simple fix.

History:

I have a 2004 S500 4Matic with about 70,000 miles on it. I picked it up with 59,000 miles. I would have liked to get something with fewer miles but I was looking for some specific options. So far the car has been much better at this mileage than my old 2001 C240 Manual Transmission was (of course, right).

The car came with TPMS disabled, but I noticed in EPC that it was built with the TPMS option. I decided to get some new tires and the BERU sensors listed as compatible. After installing the new tires and sensors, we still couldn't get the tire system to come on. After some back and forth with a reputable tire shop and a not so great European car mechanic, I decided to take it to the dealer. The mechanic at the European repair shop tried to tell me that I'd have to replace the entire TPMS controller system, not just the sensors. He couldn't even read the sensors accurately with his equipment. Some showed up as inactive. At the dealer I kind of played dumb and told them the TPMS stopped working (not true). They activated it again fairly easily, using DAS I suppose. Once that was done it was easy to reactivate the system following the instructions from the manual. It wasn't really necessary to use the manual, it was that easy.

Here's the problem:

After driving around for almost a year I had a "red alert" tire pressure warning which turned out to be a false reading. The TPMS noticed a higher than normal pressure (but acceptable) after I put some air in the tires. Shortly after that, every time I turned on the car, I got a message to reactivate the TPMS. If I pressed the little "R" button, the system would reset and it would recognize all sensors and display tire pressure properly. However, I still have to reset the system before it will activate.

Also, I thought there was a way to reset the TPMS and tell it "the current tire pressure is what you should start monitoring". I've noticed that if my pressure creeps up a bit due to warm tires, it can sometimes trip the "red alert" warning on the dashboard display. There is no way to reset the red warnings while driving.

I plan to take this to the dealer to fix this and some minor problems. Does anyone have an idea how to fix this to avoid a dealer visit?

(BTW, Keyless Entry and Distronic are the best options on the planet!!) :)

TL;DR How to fix TPMS so it doesn't require constant reset or visit to dealer?
 

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W221 & Audio Moderator
2013 S550
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10,978 Posts
My TPMS will go to a red warning if tire pressure exceeds 38 psi on any tire. If I don't stop and adjust pressure as it advises, the system will trip off and require re-initialization. Reinitializing the system is done on the LCD (multifunction) display - or, as I like to call it, the "peek and panic panel." You'll have to drive around for a while until things register - then the system will be OK.

It worked that way with my OE sensors, and with the Beru sensors I installed just this month. I had my dealer install the Beru sensors, which I supplied. When he gave the car back, the tires read 36 front, 34 rear. I was curious to see if it would work the same way it had with the original sensors, so I drove it home that way - and indeed, it did work the same way. It gave the red warning at 38 psi, and tripped off after a time when I didn't adjust.

I reset my pressures to 29 front and 32 rear to re-initialize and recalibrate the system.

After re-initializing and getting the system registering normally, I reinflate my tires to the pressures I like to use (31 and 34). The system works just fine, having done that.
 
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