Was test driving a 2016 E400. 89K KM. It was a wet rainy day. All of a sudden every fault light in the dashboard came on, individual messages came up about every safety system being disabled (blind spot assist, ESP, etc.), and the car start to drive weird. It wouldn't go over 5-10 KM/hr, and it was constantly revving up and down by itself and as a result there was rocking motion (slow fast slow fast....as if someone would apply breaks and quickly let go and quickly apply again and let go....). Turned the car off. Started again, the engine revved up by itself to full throttle and stayed there for a few seconds and then calmed down. Started to drive and after about a few meters/few seconds, same thing: every possible error light and message started to come up, and car started to rev up and down by itself when put to drive and it moved very slow with rocking (speed up and down continuously) motion.

Mercedes shop checked it and diagnosed that Boost Pressure Sensor needed replacement. I had read similar error reports and they all mentioned blind spot sensors as the cause. But whatever.

Boost Pressure Sensor was replaced. Car drove just fine after that for about 75-100 KM. It was dry and sunny though.
And then the Blind Spot Sensor inoperative message came up after another day. Mercedes shop now diagnosed it with needing a blind spot sensor.

I am wondering what else could be wrong with it? Based on well known issues expected with Mercedes of this age and mileage, is it all that I should expect to go bad, or is there something else too that could go wrong?
Also, is replacing the blind spot sensor the only thing that should be done in this case, or other things should also be replaced? Such as harness, etc.?

 

The battery and voltage converter (capacitor) are as old as 7 years now depending on build date, if they are original. Ask for proof (documentation) they were changed. If it was your car I would suggest replacing battery and voltage converter. But as it is a sale there is some risk involved.

Best case scenario it’s the battery+converter. Worst case it’s an electrical nightmare and bottomless money pit.

 

thanks!!!

Is there any way to diagnose or test that it’s not going to be an “electrical nightmare”? Any safeguards you can suggest? For example, asking for a 3 month/6K KM warranty on sensors and electrical system (with the thinking that whatever else has gone wrong will surface within that period of normal driving? Or, better avoid it altogether?

 

Run away. I wouldn’t consider a car with electrical fit problems unless they were giving it away and I had all of the proper diagnostic tools at my disposal.

 

I agree with chassis and key08, best case this is a bad battery, worst case a nightmare. There are other cars out there, keep looking.

 

Wow.... I did not know by 2016 E400 already using Capacitor for Start-Stop-Assist, or it it the baby battery 12Ah at the trunk like mine and then another capacitor like some C class W205 ?

If indeed the blind spot sensor is contributing to this sad saga, its kinda scarry because we actually traded hard earned driving skill + logic + experience to become lazy-to-be-alert-driver and later be tortured by this advance system acting up.
ADAS or any system in our car which can command acceleration or braking using its own algo, like front radar thingy.....I would not want to have such options.
If them system goes banana and intermittently without any DTC, its going to be a nightmare to troubleshoot.
I also do not want to rely on such gimmicks.

Now electrical issue aside. We discuss RADAR.
I seen the rear blind spot is a real baby sized and baby powered radar...as per youtubers who tear them apart.
I am decently good with marine radar, few thousand hours staring on them for night cruise totally radar dependent as we do not use headlights on yachts even in the darkest of night.
There are noise rejection feature on a radar, any radar actually which is called Rain Clutter and also adjustment for sea-state.
Rain or waves will cause radar reflection and it can be mistaken as target. Some good radars have true color, it can show metallic return vs weaker water/liquid based return based on color shown on display.

If anything solid, and more so if metallic, get in front of the radar antena, it may be misread as target or obstruction.
So if the rear bumper gets really dirty, there is a chance the rear radar may get confused.
I do not know how a car rear radar does its auto de-clutter algo, but it is a world a part between no rain and heavy rain in respect to the "cleanliness" of the radar return aka the signal the radar is reading.

Happy shopping.....

 

Pull codes.