Hello! I have returned here seeking guidance. The folks here have been a tremendous help to me in the past with regards to my 2002 E320, and I'm hoping you guys will be able to help me out again.

I put together video for your viewing pleasure! First 3 minutes summarizes the situation and demonstrates the issue, the rest is me messing with my STAR diagnostic system. Might be a bit easier than reading my ramble below. https://www.youtube.com/watch?v=JSXK3tvuuh4

I was on my way to work yesterday, and as soon as I turned left across the intersection and started getting on the gas (maybe 35mph or so) I felt the back end of the vehicle start to move horizontally into the lane to my right. It should be noted, I didn't hear any bangs and I didn't feel anything mechanically go wrong from the drivers seat. The only thing I heard was all the error messages popping up on the dash (ESP, BAS, ESP). I had driven about a mile and a half completely normally prior to this event. I tried to correct the sway and the whole car started fishtailing before I was eventually able to get it to a stop on the side of the road. I stuck my head underneath expecting fluids to be leaking somewhere, or broken parts hanging from somewhere but everything appeared to be intact. I managed to drive back home with the hazards on, going about 15 mph the whole way. The backend felt like it was on ice skates the whole time. I had to turn the steering wheel about a quarter turn to the left to remain going forward in a strait line.

I plugged in my STAR system and cleared all the old codes. Once I run a new test, the only fail I get is in the ESP system for the N49 steering angle sensor. All other errors are in driving irrelevant categories (Partronic system, Instrument cluster, etc). If I go to test the steering angle in the STAR system though, the angle values seem to be showing just fine so I'm not sure what the problem is there. When the quick test is running however, once it gets to the ESP section, it triggers the ESP warning light on my dash. The only warning light that shows after I first start up the vehicle following this event is the battery/alternator warning.

Right now everything appears to be mechanically normal, so I'm not sure what the issue is. My brakes and steering system seem to be normal, the backend is just so unstable I can't safely drive the vehicle anywhere.

I'm going to attempt to test the wheel speed sensors somehow (STAR says I need to get the wheels turning at least 3km/h in neutral and right now I don't even own a floor jack). Past that I'm not really sure what steps I should take next. If anyone has any ideas for me I am more than happy to give them a try, thanks ahead of time.

Sounds like someone ran either the front or rear into a curb, if no broken suspension parts are found, the fact that your steering the car off center to go straight indicates that, you can leave wheels straight and sight front to rear the wheels should be relatively straight front to back , check both sides, if that checks ok , look for bent links in rear

I’d look at the subframe bushings

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

Instead of filming the computer you should be filming the underside of the car. Get it on a lift.

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Well when you guys are right, you're right.... https://youtu.be/M7Eh3bu-S48

I'm not sure how I can go about fixing this one. I am open to any ideas.

Holy hell. You need a new subframe. There's no alternative. No welder is fixing that! Do not dare drive that car as it is, you're lucky you didn't have an accident. You weren't kidding when you said the car is not safe.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

The subframe is attached to the car with four large bolts. Drop the subframe along with the rear suspension and diff, move all the parts to the new subframe, reinstalling to the car. The rest of the car body under there looks fine, surprisingly.

This is the part you need.
https://www.ebay.com/itm/1996-2002-Mercedes-Benz-W210-E320-E420-E430-E55-SUB-FRAME-CROSS-MEMBER-REAR-/193297142044?_trksid=p2349624.m46890.l49286

Since you live in the rust belt, get this subframe painted before installing it. This is a good time to replace a bunch of the rear control arms too.

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CENSORED due to not family friendly words

well we in los angeles , never see this king of rust damage , if you cant find a subframe in your state , new or used try wrecking yards in los angeles