Forgive my ignorance, but I am at a loss here. I have a 2013 C-250 Sport Sedan. I bought it in 2015. Fast forward to 3 months ago...I am driving for about 30min and all of a sudden my anti-theft kicks in and everything starts to slowly shut down. I pulled over and was able to find a fix from another forum, which was to get out of the car, lock and re-lock 3 times....it worked! I still had the check engine light on all the way home, but a light bulb in my head went on and I remembered I had not replaced the key fob battery in about 5 years....I did that and like magic, the check engine light gone. No issues for 3 months!....but yesterday, I again was driving for about 30min, got off the freeway, waiting at the light and it all happened again.

I got up this morning, everything is fine. So my question is....these key fob's "talk" to the car when you put them in the ignition right? Could this issue be a "short" or something in the key fob itself?

I am trying not to take it to the dealer yet, because of course nothing will happen when they have it and I will pay money for nothing....

I look forward to any advice.

thanks!

When the check engine light is on get the code. It is more than likely still stored in the ecu so check that first

thanks...I have a code reader that links into my Bluetooth, will give it a shot.

Nothing came up...I guess the next time it happens, I will pull over and get the codes when everything starts to shut down

Don’t know where you got your fob battery from, but I went through a period where I was receiving counterfeit batteries that died in a month (from Amazon). I ended up going to the local drugstore to make sure I was getting real ones, and that was a year ago - so far so good.

Also there’s a thicker version of the same diameter size, I forget if it’s 2025 or 2032, but the thicker one both lasts longer and seems to fit better in the fob.

Maybe you are right? I bought my new ones at Target and like I said earlier, the check engine light went away as soon as I popped it in. But yesterday, the check engine light did not come on yet, it was only the anti-theft kicking in....I can only think that the Fob and Car had a moment they were not "speaking" to each other and that set it off? Not sure...

The battery I got was 2025...so are you saying the 2032 is the same but thicker? You could be right if the battery is too thin and not making a solid connection all the time.

2032's are thicker and what I use.

It's abit of a tight fit, but it works well.

Those small batteries are really hit and miss. Some last for years others for weeks. I have had a package of 4 one lasted a month one 3 years and the latest one has been ~5 months now

I get the MB packaged batteries (2025s) from the dealer and they have all been good for a year or more. We replace them every year at the annual service.

Am I the only one who thinks of this when someone says annual?

This. Use 2032's and don't buy them off eBay. Odds are they'll won't be genuine.

LOL, showing my age and my background.

Feedback appreciated, but I don't think there's any way that key fob problems could create (or eliminate) a check engine light. They're completely separate systems. For lots of one-time issues, the CEL will go away after the engine has completed a certain number of start/run cycles without further problems.

Just for reference on the battery size "2025 or 2032".
The first 2 numbers are the diameter in mm, eg 20 = 20mm
The second number is the thickness 1/10th mm sizing.
So 25 = 2.5mm and 32 = 3.2mm thick.
One of my fobs had 2 x 2016 batteries in it when I purchased my wagon.