Just happened today. Yellow tire pressure warning light showed up. I tested tire pressure of all four tires they are all 38psi. Maybe it’s time to replace the tire pressure sensors. They are original and have never been replaced on this 2007 GL450.

yes another possibility would be the spare tire. Will check its pressure.

 

Yes, it’s very likely one or more sensor batteries at end of life.

If you don’t wanna spend the $5-600 this will cost to fix, just live with it. Check the tires frequently.

Or disable it in XEntry developer mode.
TPMS is not required on 2008 and earlier.

The spare tire does not have a sensor iirc.

 

Thanks a lot for the info. Discount tire sells tire pressure sensor for $60 each installed. I might give it a try.

 

Just be sure that they are the correct frequency and you should be good.

 

On my 2009, after gauging my tires I reset my TPMS via the steering wheel controls.

 

With a better scan tool, e.g. MBII, you can pull the actual pressure readings being transmitted. Thus you can compare the TPMS transmissions with the actual pressure tested via a gauge.

When you press the R button while in TPMS dash mode, the system accepts the current pressure transmissions as baseline. If you have a sensor transmitting bogus low pressures, you can simply Reset to make the error message go away. You can also Reset to get rid of the persistent error message when airing down for off road purposes.

Note that the orange dash warning light also comes on in response to wheel speed differentials. If one wheel is persistently turning faster than the others, the system assumes this is due to low pressure.

Given all the headaches TPMS causes, and the fact it was not demand driven - customers really wanting a way to monitor actual tire pressures - but rather so we can Save The Planet, I honestly would prefer to disable the system and just go with the wheel speed differential.