richardliebert

I recently had my dealer replace two tire pressure sending units because the two wheels in question were frequently reporting low tire pressure. I am sure the problem was in the wheel because I first evaluated the sending units by rotating the wheels in question and, sure enough, the error messages 'followed' the wheel.

Now the TPMS resets itself 5-10 minutes after I start the car. It takes about 5 minutes for the display to restore, which I realize is normal. What the heck could be causing this?

Feel free to comment.

Fraser

TMPS control module issue.

Corsa9000

In my car all four wheels shows 40-41 PSI (cold tires) while I have 32F, 35R. The pressure gauge I use is a very high quality unit but I suppose it could be out of calibration. Do you think TPMS sensors are bad or something else going on?

Thanks.

richardliebert

I use a digital tire guage also. The two sending units I replaced were reading high, just like yours. The new ones are perfect.

I may have a resolution to my original "reset" problem. I placed the two bad sending units in the trunk at the dealer because I wanted to keep the old parts. They may have been confusing my system and causing it to reset. I removed them from the car just now. I'll post the outcome in a day or two.

Skylaw

I have two sensors doing the same thing - reading much higher pressures than are actually the case. That's a sign of a failing battery in the sensor(s). When it first began I had yellow warnings and a "reset" instruction in the instrument cluster. Once I had driven and the high-reading sensors had come down (a sure sign of a problem; as tires heat up, the actual pressure increases - but mine, per TPMS, went down), the system will reset.

Now the batteries are so bad it won't reset; I get the red warning. Time to replace them all (and I'll use the Beru sensors from The Tire Rack when I do).

Corsa9000

Thanks guys. In my case, I am due for four new tires next month so I will have the TPMS sensor batteries replaced as well.

Skylaw

Corsa,

The entire sensor is replaced, not just the battery. The battery is integral to the sensor. Also, if you buy from the dealer, expect a price over $1K for four. Check with The Tire Rack. The sensors for the W220 are not listed on their website, but they have them, and know exactly what you need - $275 for four (last time i checked).

bzliteyear

Hmmm....
My left rear reads hi...44.
I let some air out but still read the same.
Shall I reset, or is it supposed to auto adjust?
PL

richardliebert

Update on original post: If you recall from my earlier post I realized that I had asked the dealer for my used TP sending units and subsequently left them in the car, duh! Since removing the used sending units from my car the display has stopped resetting itself. Everything appears to be working fine.

Next time this happens (and it will on the left side) I'll buy sending units from tire rack and have my local tire shop install them. I was quoted a price of $20 per wheel for installation just yesterday.

Skylaw

You need to check the pressure with a reliable gauge. It should be obvious from the preceding posts that you have either an over-inflated tire or a bad sensor (probably the battery). Because you let air out, possibly without checking pressure with a gauge, you may now be driving on an underinflated tire.

If the batteries of the sensors are failing, the sensors will not "auto adjust." They will stay high. As I described above, if you drive with the high reading and it comes down as your tires heat up, it's a very good indication your sensor battery is failing.

Trinsoca

I had my two rear tires replaced about a month ago (2005 S-500). While at the shop the tech showed me the sensors and said that I will have to replace them some time soon. Now 300 miles later my left rear tire is not reading at all. The dash is saying take to workshop, so I would like to replace all of the sensors. Skylaw are the ones you mentioned (Beru) earlier from tire rack any good? My local tire shop said that they are not good quality and do not buy those.

Skylaw

I haven't installed them yet, but plenty of forum members have, and they report good results.

bzliteyear

Any thoughts? My manual gauge is 6 pounds different than the dash - I'm assuming I go w/ the manual gauge of matching the mfgr's 35 lbs for rear?
PL

Skylaw

You need to follow what I will label an initial calibration procedure that is in your owner's manual (my manual terms it "reactivating" the monitoring; it is done in the instrument cluster display). First, be sure your tires are set to 29 front, 32 rear, cold readings. Follow the owner's manual instructions to reactivate (reset) the system. You will then have to drive around for a while; mine has reset in as little as 5 minutes, and has taken as long as 20 min.

After TPMS has reactivated and calibrated itself, you should see pressures close to 29 and 32 (perhaps slightly higher; it depends on how long the reset takes, and how fast you drive). Importantly, the front tires should be close to one another - within a pound - and so should the rear tires. The fronts and rears will still differ. If they system has calibrated properly, on your next cold start, the system will read 29 front, 32 rear.

Once you have done this calibration, you should be able to inflate your tires to your preferred pressures, and the readings should be accurate on the TPMS.

If your system shows things differently, you either have a sensor problem or a controller problem. As the posts above reflect, an initial (cold) reading that is significantly higher than actual pressure is a good indication of a failing sensor battery - especially if the high pressure reading pressure comes down as you drive (in a normal system, the pressure would go up, not down, as the tire warms up).

Those are my thoughts, and that's about all I can say - except that this was pretty much covered in the W220 Owners Start Here sticky, in the TPMS links.

Trinsoca

I ordered the Beru, TPMS from Tire Rack today and they should be here Thursday. I will be out of town on vacation and as soon as I put them on I will let everyone know how they work. They cost $95 each plus tax and shipping, total was $420.

Corsa9000

Thanks Skylaw for the all the info.

I have to say for people who pay attention to their tire pressure and check them regularly, TPMS has a lot of unnecessary hassle. Didn't they become mandatory when all those Ford Explorers were tipping over due to low tire pressure?

scarybary

I have the tire rack sensors in both my snow and summer tire sets and they work perfectly.

Trinsoca

Well yesterday I went to the tire shop (will not mention name) that put on my 2 new back tires about a month ago, to have all 4 sensors replaced. The guy tried and then told me that they cannot work the valve stems are too short. They did not seem to have much experience with this type. I had to go back into the work shop and show him how to adjust the angle for it to fit which it did. After replacing all 4 I did the re-activation and drove, and drove and re-activate, on and on etc nothing working. I went back to the shop and collected the old parts and guess what I did, I put them in the trunk and the system got worst. Reached home frustrated and went to this forum and remembered, Oh foolish one, it's reading the old ones in the trunk, took them out re-check the pressure and WHOA!!! works fine. I checked the pressure this morning cold and they read exactly what my mechanical gauge reads.