I’ve got a 2011 Mercedes-Benz E350 4MATIC wagon with 257k miles. About 90% of the time, I get a “Tire Pressure Monitor Inoperative” warning at startup, but around 10% of the time there’s no warning and the tire pressures read perfectly. Even when the warning appears, the system still shows correct readings if a tire goes flat.



I’ve confirmed with Discount Tire that all sensors (three Schrader 433 MHz from them and one OE sensor) have good batteries and are properly registered to the module. All are the same brand, all reading correctly, but I still get this annoying inoperative warning. Any ideas if I need to re-register them with XENTRY or if there’s another fix?

Great detective work there. TPMS can be a pain for anyone to deal with... I've had my share!

Your inputs show us :

1. good 433MHz wheel sensors
2. good sensor receptions
3. good sensors Pressures + Temps
4. good TPMS Module reception
5. good IC Display data across CAN-B
6. All good then....

Let's say Sensors are now proven working well beyond reasonable doubt - There is nearly no reason your TPMS is not working...
yet that's why we're here.

-- Use your OBDII scanner to interact with your TPMS module across the car CAN-B network. See what data it is exposing or not. It is located in the wet area over the axle near gas fill door.

-- Scan the whole chassis to see how many goofy modules are actively disrupting CAN-B COM's.

-- Personally I would try to refresh TPMS module then eventually sanitize CAN-B + Gateway with a battery disconnect to reboot the whole chassis.

Report progresses.


+++++ OBVIOUS STEP: SAVE THRESHOLDS
This step is obvious to many but not everyone:
sensor threshold need to be latched in the TPMS module once so that it has a reference to stand guard.

Practically you want to register wheel pressure ONE TIME initially after driving when tires are at normal operating temps. (Say : 34Psi Front + 38Psi Rear).

From that point on TPMS will warn of any tire with significantly lower pressures (-5Psi).

The key to TPMS is threshold must be set. This is done using the IC Display menu and your steering wheel buttons, right?

> TROUBLESHOOTING is not about swapping random parts!
TPMS is a well built module with a gold plated circuit board - However it is connected with a leaky harness connector that can swamp it with water.
Let's see how live module operates...

Thank you so much for your quick and concise reply! I’ll get with my technician at the dealership to have my vehicle plugged in to Xentry to see what CAN – B issues I can find. I’m assuming that I can get to the module by removing the passenger side, rear fender liner, correct?

Thanks again!

Don't rush to conclusions... scan the chassis for condition.

> Less Likely:
To remove TPMS remove the rear passenger side wheel only. There is extremely little room to work screws out

The TPMS module is not very user friendly to remove ie. be sure you have good reasons to removed it...


> More Likely:
Double check with scanner/Xentry no other bad modules are impacting normal CAN-B traffic.