KiloWatt

Hi Guys,

Recently, our two W221s both developed an almost similar ABS, ESP, Distronic etc. inoperable issue even though the vehicles are quite different, 2009 S600 vs. 2007 320CDI, and are located very far from each other.

When the cars have been sitting over night, they start and drive just fine. However, if the car has been parked for a couple of minutes after it had reached normal operating temperature, as soon as the door is opened there is that dreaded warning gong and Release Parking Brake is displayed in red letters.

Switching on the ignition makes all the usual vehicle dynamics faults come up in the display, like ABS, ESP, Distronic etc. inoperable. When the engine is started and the car driven for a couple of 100 feet or more, then stopped, the engine turned off and then directly on again, the warnings disappear and everything is fine for the rest of that drive!

So, while the the faults where displayed, I connected the SD laptop (engine not started, only ignition on) and found out that one of the wheel speed sensors (right front S600, left front S320CDI) was reading random crazy speeds (and in the instrument cluster speedometer, I could see up to 320km/h ). So, I ordered a new original sensor directly from Mercedes, installed it, cleared all faults and ...... NO difference unfortunately! Exactly the same weird behavior with the new sensor.

What on earth could cause this issue in those two cars? N47/5 connector corroded? Cable problem?

I guess the Release Parking Brake warning is because the car thinks it is moving due to the crazy speed sensor readings. But where can these faulty speeds come from instead of the sensor itself?

Thanks for any help!

vettebk

Very weird. Can you pull codes? Do you have a gravel drive-way?

BOTUS

the front hub inner seal is part of the sensor / reluctor relationship - it can get all the rust and disc wear filth clog it up, as somehow its magnetic

on the rear wheels its a different design and the ring corrodes and falls off

any build up will, alongside the designed to fail sensors cause issues

KiloWatt

Yes, interesting. Maybe, all the filth can trigger the sensor to fire at a high chaotic rate while nothing is spinning....

Actually, I did try to clean through the hole with a paper towel wrapped around a stick and turning the brake disc and with compressed air while turning the disc. Maybe it was not enough to clean it...

KiloWatt

I can try to work a little more with Xentry SD, but I think it was all "!" instead of "F" and then I found the rogue sensor readings, which thought could be rectified by a new sensor.

Another weird thing was IIRC that Xentry at first was unable to initiate/find the ABR module, but succeeded when I tried once more.

A big Mercedes Center suggested it might be a low voltage problem, but that was before I had found the crazy speed readings from one of the sensors. I mean if the N47/5 thinks one wheel is spinning that way nothing can work correctly...

And yes, there is some gravel on the paved roads here once in a while...

BOTUS

ABS modules like to die on ALL BRANDS OF MOTOR VEHICLE - they designed them to die - but merc ones are specced to last at least 10 times the length of the BM trash

often no comms with the module is a normal consequence of the failure modes built in.... lots of places can fix the deigned in faults and offer life time warranty and then no coding fun refitting your old unit

a UK place - as its just for reference....

https://www.ecutesting.com/product-c...dule-combined/

vettebk

Our W221s hate low voltage. I would check the dates on the batteries and recharge them fully and test with a voltmeter. I suppose you could also have a bad "new" wheel sensor or a bad connection. I would recheck your work on the replacement sensor. I have heard of gravel roads causing damage to sensors, but usually it is on an unpaved driveway gravel covered and the driver was going fast (he shall remain nameless but he drives an S600).

KiloWatt

Yes, there is a company near me that fixed the amplifier that goes bad sooner or later. Has worked great since...

Is it possible to just unbolt the N47/5 ABS module from the hydraulic block or does one have to mess with break fluid and stuff with cleanliness issues etc.?

KiloWatt

The battery is original Mercedes AGM and quite, plus kept in perfect condition by a very advanced charger when the car is not driven. And when the car has been sitting a while, the cold start does not show this weird fault.

Maybe a ground point has gone bad and causes voltage issues for the ABS module under certain conditions...

BOTUS

yes it just unbolts - just be careful with the multiple dangly bits that are left floating

in the old days the failure was just a link wire that "accidentally" fell off between the circuit board and the mutliplug - just re-solder
but today the ESP pump motor brushes gum up with carbon dust - meaning the brushes wear funny or don't make contact