AbeLincolnTownc

I have a 2018 C43 that I bought over the summer last year and the car has been rock solid and a total joy to have. I transferred my plates from my previous W204, so when my registration was up this month I took it to get emissions tested and the O2 Heater, O2, and Cat Sensors all came back in a "Not Ready" state. That was a little odd to me since I regularly drive the car (in varying conditions) and it's never thrown a CEL or other codes. I figured it was a fluke so I left, took it on a pretty spirited drive over the weekend and took it back. Same results. So on my way home I stopped at O'Reilly's and got a relatively cheapish OBDII reader and discovered all three of the above mentioned sensors were outright disabled on the car.

It was at this point my eyebrow raised a little bit--it was odd to me that the sensors were showing disabled but no other codes had been stored on the car (the folks who did my pre-purchase inspection cleared them before I bought it and it looks like it's not thrown any sense). So I started doing some research here and saw some other folks mentioning that an ECU tune--specifically Eurocharged--will disable those particular emissions sensors. I shot an email off to Eurocharged about it with my VIN and haven't really heard anything definitive back yet, but figured I'd see if anyone here had any thoughts/insight. If it does have the tune I'd honestly be thrilled--I'd been considering it anyway, but my most immediate concern is determining why/how these sensors were disabled and getting them compliant long enough to pass emissions.

For whatever it's worth, I also reached out to Renntech and AMR to see if they'd done any work. Renntech says they haven't, no reply from AMR yet.

Thanks all!

C43HeartBoost

Normally you will throw a CEL after approximately 50 miles if your o2 sensors are not working properly. Generally speaking, only stage 2 tunes alter/suppress the o2 CEL due to high flow cats or catless downpipes being required to go stage 2. You may want to check to see if your downpipes are stock and/or if your cats are still on the car (from the top, the driver’s side is pretty easy to see).

AbeLincolnTownc

I've not thrown a CEL (or any codes for that matter) in the 10 months I've had the vehicle, so I feel like if it were really faulty sensors that'd be easier to diagnose. It's just like the sensors are disabled entirely and that's what's throwing me with this whole thing. The OBDII reader I bought still shows live data temps on both cats too, so I have no reason to think they're not there.

I'm not opposed necessarily to replacing the sensors if I need to, but at this point I'm just incredibly curious what's actually going on.

Fluffy Nuggets

So are those three monitors( o2, o2 Heater, and Cat) normally turned off when going stage 2? I recently went stage 2 with high flow cats and noticed these monitors are not ready/disabled even after trying a few drive cycles. I have a cheap OBD II that gives me a code for a slow responsive o2 sensor( pre-cat o2, not the ones with spacers), is this normal?

MaverickC43

Figure anything out?
there are people who think my car may have been tuned before I bought it used due to my dragy times.
any way to find out.
I’m not sure I want the dealer involved yet.

AbeLincolnTownc

Nothing yet. Renntech says they have no record of that VIN, I spoke with AMR a few minutes ago and they're checking now. I talked with Eurocharged on the phone this morning and they said they can't track tunes based on VIN, that they're tied to who originally purchased it, so they can't tell definitively one way or another.

Eurocharged did seem to think a reflash back to factory was going to solve the issue, so that looks to be the route to go down. It'll end up costing me the price of the entire tune/handheld from Eurocharged or I can bite the bullet and see if the dealer will reflash it without them having a cow about it..

C43HeartBoost

An MB dealership should be able to flash the most recent version of the ECU software and it will remove the tune.

AbeLincolnTownc

Yep, I talked to one of my local dealerships today and they told me they'd charge me $250 for diagnostics and assuming they didn't find any compatibility issues/errors they'd reflash without any additional charge. Eurocharged quoted me about $1500 for the Stage 1 tune (with the option to reflash to stock and back). I'm leaning toward doing toward the Eurocharged--even though I don't really know definitively if the car does have an active tune right now, the idea of potentially losing 100+ horsepower makes me feel like I'd immediately regret it and then I'd end up buying the tune anyway.

The whole thing has me really stressed out--didn't expect such a dilemma in trying to renew my registration.

AbeLincolnTownc

I have an update in case anyone is interested:

I elected to buy a new Eurocharged tune and immediately after getting it I flashed their tune file on it and found very little change in behavior to the car. Drove it that way for a day or so. Then I re-flashed the stock file on it and it turned into an entirely different car. Much more subdued and generally restrained versus what I'd been used to. I immediately knew at that point I'd been unknowingly driving this car for about a year with a tune already on it. Did some highway driving later that night to try and get the I/M sensors to read and they all promptly changed to a "Ready" state other than the EVAP sensor, but I guess that one is a little temperamental to read sometimes. Anyway, took it and passed emissions this morning since I'm allowed 1 Unready sensor. Got home and flashed back to the EC tune and it immediately felt like the car I knew again.

Thanks everyone who helped me troubleshoot and diagnose this!

MaverickC43

That’s crazy.
I might have to go test drive another used c43. But I still don’t think mine is tuned.
but I should go compare

C43HeartBoost

Your car is the fastest “stock” c43 that I have ever seen (on this board or otherwise). As such, I am not sure that trying another car will provide a relevant data point, as I am sure it will be slower. I am confident you are a good/great/amazing driver, but your times 0-60 are a second faster than stock and 1/4 are .7 to .4 faster than all others. C&D and R&T drivers are great and do a .2 or .3 second deduction for 1ft roll out, but your Dragy times are in a different league.

MaverickC43

Would that help explain why I got little improvement with jb4?
BMS thought my logs looked normal for stock
🤷🏻‍♂️

MaverickC43

Where do u guys get
0-60
& 1/4 mile time
ive seen a lot of 4.1-4.2?