Tifoso48

My wife was driving this afternoon, giving me time to fiddle around and I looked at the AMG Performance on the center screen, which among other readings also provides tire pressure.

I noted rear left 36 and rear right 30, which clearly is way too low especially on hot tires.

I had jus picked up the car from service and knew the reading was odd.

So, I asked her to pull up the "service screen" in front of her to compare and the readings were totally different rear left 38 and rear right 33, still way to low.

I am sure both readings pull from the same source, how can they be different - and which one to believe?

Plutoe

forget for now what the gauge says-------find a small tire pressure gauge and manually check the tire pressures----what are they---then go from there

ygmn

Who knows how accurate TPMS sensors are.

Get a good tire pressure gage and note the accuracy of the one you choose.
most are 1% of full scale.
so makes sense to use one that the max pressure is just above your normal setting and for these cars 50PSI gage is fine.

RTC63

My SL63's TPMS sensors seem to be very accurate so far...
Sometimes the system needs to recalibrate and it takes time...

superswiss

TPMS systems on average are accurate between 1-2%, but good ones are accurate to within about 1 psi. From my observation the MB system is accurate to within 1 psi. But as mentioned above, TPMS shouldn't be used to check your tire pressures. It's more of a piece of mind to see if the pressures are about what they should be and not completely off from expectations. You should use a tire gauge to adjust the pressure when the tires are cold, so you know what they actually are and then see what TPMS says to determine the accuracy. Then you can extrapolate from that and spot issues. Also keep in mind that pressures rise as the tires heat up. Every 10 degrees Fahrenheit results in a 1 psi change. Since the AMG display shows pressures and temperatures, you can do some quick math in your head to determine if the pressures look good. For example if you see different pressures between left and right tire, look at the temperature of each tire and see if the pressure difference can be explained that way.

In your case it looks like they are indeed off and probably haven't been set correctly by the last person who checked them. When I have service done on my car I always make sure they don't touch the tire pressures. I have a standing no wash, no adjusting tire pressures order with my SA. So as said, get a trusty tire gauge and adjust them correctly, reset TPMS and take it from there. As for the service display showing different pressures than the performance display, not sure what's going on there. To be honest I never check the pressures in the service display. I pretty much always have my instrument cluster set up like in the picture below, so I can see all the temperatures and pressures while driving. Since my car is RWD I want to be aware of the tire temperatures to gauge the level of grip at all times.