cheerful

Interesting thing happened when I replaced all 4 tires and the front right wheel.

After that, the tire monitor shows 2 left at 39 and 2 right at 45 -- the norm is 39 front and 45 at rear. I went to the air pump but they appear to be 39 in front and 45 at rear. I was quite confused and took it back to the tire shop

The guy told me I need to reset. The only thing I can find is to go the tire monitor, press down arrow, choose the use it a new reference. That did not change anything. The guy then connected to OBD and did something. Then it's corrected.

I would guess the tire pressure monitor has some kind of setting to determine which tire is at which position. It has some king of memory and is probably linked to the wheel somehow. The new wheel probably played a role to mess it up.

Does anyone know how this should have worked?

Thanks

W205C43PFL

There are sensors for each tire. The device they used is precisely used to communicate with the sensors.

cheerful

There is sensor on each tire / wheel.

However, how does the car knows the position of each senor/wheel/tire? Naively, I'd think it's determined by the parts on the car, not the part on the wheel. But if that's the case, I don't see why after replacing wheel/tire, the position was wrong. Or maybe the tire shop messed things up

W205C43PFL

Hmmm, sorry I didn't get your question, are you asking that how come if you rotate the tires with the same sensor in each tire to the front from the back, the vehicle still identifies the right tire for the right side?
Let me read your original post again.

cheerful

After the 4 tires and FR wheel (note I have no idea if they put the new one at FR) were replaced, the dashboard showed the following

FL=39 FR = 45
RL=39 RR= 45

According the the air pump, it's

FL=39 FR = 39
RL=45 RR= 45

The tire shop guy used OBD and did something and did not move wheel/tire. The the tire reads correctly

FL=39 FR = 39
RL=45 RR= 45

So in the car computer system, the position of the wheel/tire is somehow messed up (e.g. FR <-> RL).

W205C43PFL

I see so ya as you know, each sensor communicates with the computer individually so I guess the person told the car computer which sensor is which tire then. They all have a unique identifier so probably is to just assign each identifier to each wheel.

Happeedragon

could it be possible that each wheel's sensor transmit to receiver near that particular wheel area so it does not matter even if the wheels are rotated, the receiver location is fixed. The ECU will get the correct corresponding info from that particular fixed position receiver.

cheerful

If I'd design this, I'd set the position information at the receiving end in the car. The sensor tells the receiver. This way rotation would not require any change in the car.

But given the wrong reading I saw, I'd say that's not the design. And each time they rotate the tire, you have to go into OBD to do something. This sounds wrong.

W205C43PFL

There is also a handheld device that you can assign values to the TPMS sensors and adjust accordingly, it is solely designed for that purpose.

As for your design, it is a great one, a receiver receiving sensor information based on the distance on the two axis seems like a good idea. That way, it can predict where is each sensor and on which wheel but there might be technical limitations that made engineers design it to use the method that is being used now. Interesting idea nonetheless.

cheerful

For all practical purpose, this means each time they rotate or replace wheel/tire, you'd have to pay a bit attention to the tire pressure monitor. In my case, it alerts right away that the left rear one has issue.

benzdude

My MB tech recently put the wrong tire sensor on two wheels of my car.

There was lots of head scratching the next time I tried filling them with air. Why won't it increase!

cheerful

That was what happened to me. I saw the air pressure incorrect after the car is out of the shop. So I tried to use air pump to correct it but it does not move as expected. So I had to go back to the guy in the shop who also tried air pump first and then went with OBD.