I finally broke down and took my car to the mercedes dealer and asked them to fix the Check Engine Light. I had built one of the code readers and it was telling me I needed a new speed sensor but I didn't want to go replacing parts willy-nilly.

The dealer said, "You needed a new O2 sensor."

That never came up on my LED tester. I said "Do you promise that will fix my CEL?"

He said, "yes."

"Go ahead," I replied.

I called this morning and the car is fixed. $300.17 but worth every penny. I had spent hours with the LED tester, clearing codes, trying to figure out what they meant and being sent off in all directions. The moral of this story: Not all things are best done yourself. Yes, I could have easily changed the O2 sensor, and I have done so on other cars. Yes, I could have bought the part for less than I paid the dealer. But the point is, how many other unnecessary parts would I have purchased and installed because I didn't know the real problem?

To each his own. Obviously not everyone is a DIYer. If you didn't enjoy the chase you're probably not cut out for it. I just paid $84 for an O2 and it will go in in about 20 minutes. When I guess wrong and put in a part that doesn't fix the problem I chalk it up to preventive maintenance. But agreed -it really doesn't make sense to do it both ways - invest your time, abort, and then spend the $300. I personally question whether it makes economic sense to own these cars (e.g. a 94 MB) if you go the $300 route. But again to each his own.

Seeing that your DIYer tool had detected speed sensor stored fault/codes, I doubt your problems are over with an Oxygen Sensor change..
Hope they are , but the two are not in the same bag and I for one will be surprised if codes do not re-appear in a few days.
At least the Dealer has guaranteed this as a solution, so you have that to work with..
A stored fault code can be a trying diagnosis , but I can assure you that there are many, many DIYers here that have saved a small fortune by retrieving codes, chasing the possibles , asking ,listening, and investigating the problem with the help of this group... and , believe it or not, solving the problem.
Good luck.

I think the 'economic sense' comes into play when you have not made a car payment for almost two years, have a car with 239,125 miles and still drives and looks better than 95% of the cars on the road. It does require a lot thoughtful maintenance and almost becomes a hobby. The wagon always gets me and and the kids home everyday thanks to guys like you who share their experiences and opinions.

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles

I can vouch for that! This site and people like Arthur (and many others too) have helped me solve some interesting problems and taught me to be a better diy'er.

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Glen Tokuhara
Beauty & the Beast and the wagon that could!

I am not saying that I am not cut out to do my own work. After all, I have have done so for almost 35 years. I have rebuilt engines, replaced clutches, headgaskets, starters, done all kinds of brake jobs and many other things. I am only saying that my O2 sensor problem did not present on my code reader. I took a reading on the morning that I dropped the car off to the dealer. I still got the speed sensor fault. So I am confused. Also, the dealer did not get a speed sensor fault, but rather a faulty brake stop switch - which I had replaced at the start. He said that I must not have cleared it correctly. I think the dealer must use a slightly different code reader.

If I do get the CEL again, I guess I'll bring it back and say - hey, you promised this would fix the CEL.

There have been a few times when I have been stumped, I can see why you would take your car in, a CEL light would not come on for a speed sensor, that would be your ABS or ASR. The Cel notifies of fault with emissions and engine controls. So when you get a code like that from your scanner, I would doubt the scanner, or the documentation used to determine what exactly the code was. We all learn new things every day and the ability to be open minded and patient goes a long way, but we need to realize when our time is worth more than what it would cost to just have the darn thing fixed by an expert. Happy Benzing!

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Brian W. Heitman

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