rios33

hi all, I drive an 08 ML320 CDI,

Had this come up, had it fixed at the dealer. The drive home from the dealer, it popped up again, took it back and they fixed the other TPMS sensor and kept it overnight to make sure it would not happen again. Take it home from the dealer, happens again.....

Had the next two replaced at a discount tire, because its way cheaper and tried to reset the light using the steering wheel display and the TPMS light will not go away and after driving it for 20 minutes or so, it flashes "Tire Pressure Monitor System Inoperative"

I know the system is working because I had a flat tire two weeks ago, while this whole situation is going on and it told me my tire pressure was low (in red) and it was right.

So now after having all 4 sensors replaced, the light keeps coming on and I am wondering if there is a way for me to reset it??

Any info would be great as I am growing rather impatient with my first Benz.

N_Jay

Guessing it has always been the receiver and never the sensors.

rios33

I had asked the dealership about the problem being whatever it is that the TPMS transmits to and he told me no, that the sensor was dead, but he did say that there was no signal to the receiver. They have some way to test the sensors, I guess they really never checked the receiver.

Thanks for the reply, I hope someone else has had a similar problem and can give me some more info

rios33

Upon talking to some people here, it seems that Discount Tire installed the TPMS with the wrong frequency. They installed the 315mhz version, where as the part number from my dealership invoice shows a 433mhz TPMS sensor.

Will have them install them sometime this week and hopefully it will be taken care of.

eeferber

yep, 433 is the proper frequency

dgiturbo

I am getting this same TPMS Inop message on my 07ML 320CDI. Being 7 years old, my guess is the sensor batteries have finally died.
My plan is to replace them with non OEM, as MB is really proud of theirs, pricing them at +$250 EACH.
Anyone else have this, and if so, did this fix it? Also any ideas as to where to get them?

rios33

I believe it would be cheaper to have them replaced at a Pep Boys or a Discount Tire rather than the dealership. I would call and ask for pricing beforehand, but make sure they have the proper frequency sensors in stock, the 433mhz.

They told me at Discount that their "computer shows the 315 as the right one" but it is not, so tell them what you need.

Good Luck.

rios33

Finally had the rear sensors put in at discount tire, they gave them to me for free because I had to wait two months before they could get their hands on a set.

Unfortunately, they told me that all of the sensors were working fine except for the right front TPMS sensor. This was just installed by the dealership under warranty in August.

It seems odd that it would have already gone dead within three months. I am no longer under warranty and don't know whether or not to contact the dealership and tell them the part they put in was defective or just go back to discount tire and get a new sensor put on.

So far this is the only issue with this car and it is driving me crazy!

rios33

So still have this stupid light on my dash, took it to an independent european car specialist to see what is going on.

He told me that the back to TPMS sensors (installed by Discount Tire) would not report to the control unit. He said it is because it is not the same brand as the OEM sensors and that it does not matter that the replacement sensors have the same MHz frequency the CDI requires.

Also, the sensors on the front two tires now show a weak signal and he thinks it is from the new tires being put on at discount tire and them possibly damaging the sensors.

Does anyone have some TPMS knowledge to know if this car is so picky about the brand of TPMS sensor?

dgiturbo

Not sure about the brand compatible issue, but I am now waiting to borrow a set of ML wheels from one with the system working, to see if the computer will "see" them. My new VDO sensors that are on there now are also not reporting to the computer like yours.

I have been doing a lot of research on this issue and on TPMS systems in general. The sensors are not that complex where this should be such a problem. They just transmit the ID# every 55 or so seconds, unless there is a change in pressure, where it transmits every .8 of a second or so. There is also a temperature sensor in there, where it shuts the sensor down over 120C.

There are 3 main parts to the system. The 4 wheel sensors, 3 booster antennas, and the main control unit. If the wheel swap test will proves for me whether it's the sensors being a different brand than factory, or if the control unit has failed.

FYI, I also came across a TSB T-B-40.15/57 where the fuel pump can cause interference and trigger this error, but mine is out of the VIN range for this error. Also I have never had a TPMS issue since new, and the fuel pump was replaced in March this year.

Keep me posted on your progress.

dgiturbo

N_Jay wins...

I just replaced the control unit/receiver with part # A1645404701. It is in the right rear access panel tucked in by the fuses. Two plastic clips secure it in it's bracket, and the electrical connector has a locking lever clip that rotates 90degrees before it can be disconnected.

Put the new control unit in and no more issues. I restarted the TPMS and tested perfect over an hour toady.

rios33

Bringing this back from the dead but I have an update:

My TPMS issue has been fixed.

At last post, I went to an independent guy to have him look at the sensors and basically what he told me was some crap. I took the car to another guy who had a TPMS tester, a digital read-out tool, which he let me use myself. You go around from tire to tire and place the tip of it at the air stem and let it read the sensor.

Turns out that the right front TPMS sensor was a 315MHz, not a 433, which is what has been causing the problem the whole time.

I had some issues with Discount Tire ruining my tires when they were dismounting them and I am about 99% sure that they broke the sensor and replaced it with a 315MHz because that is the sensor they show in their system (which is incorrect for this car). So anyway, I had the right front sensor replaced and just like that the TPMS light went away.

It really frustrates me that a place like Discount Tire and even the first independent mechanic I went to could not just tell me that the one sensor was the wrong frequency. I had a tool and figured it out within 5 minutes and these companies deal with these types of problems all the time. Really makes me wonder if they do any good at all.

Happy to have my TPMS light off!