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

www.MBCA.org/northtexas

Join MBCA!!!

Brian,

You said it exactly right. Why not use whatever tools are at our disposal to keep our cars running right and to minimize lost time?

I have a 2001 Japanese SUV that had the CEL come on at 30K. I took it to Autozone, which provides free code reading for cars with OBD II. Its codes were for the O2 sensors. In this case there were four, and the code reader didn't say which was bad. I decided to take the car home and inspect all the connections before I purchased a new O2 sensor. As I was leaving the parking lot at Autozone, my battery went flat. They checked the battery and it was toast. I bought a new one right there. The guy cleared my codes, and no CEL ever since.

My point is that I don't have total faith in the code system.

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The code he was getting was from the CEL/DM and is a speed signal/code #20. ...Which will trip a CEL.
The reason for the tool suggestion was to get to the EA/CC module for further . more specific diagnosis.
Which is the purpose of the tool .. These 124.032 were the last of flash code/led possible retrieve,... so the tool.

Thanks Aurthur,
We all learn new things every day.

__________________
Brian W. Heitman

www.MBCA.org/northtexas

Join MBCA!!!

I wish my problem were as inexpensive as yours! My check engine light is on because I need a new throttle actuator. About $800 or so to replace. I know it's the culprit because the dang thing is making noise too!

__________________

Current:
2014 VW Tiguan SEL 4Motion 43,000 miles.

2016 Hyundai Santa Fe Sport (wife's).

Past:
2006 Jetta TDI 135,970 miles. Sold Nov. '13.
1995 E-320 Special Edition. 220,200 miles. Sold Sept. '07.
1987 190-E 16 valve. 153,000 miles. Sold Feb. '06.
1980 300-D 225,000 miles. Donated to the National Kidney Foundation.
1980 240-D manual, 297,500 miles. Totaled by inattentive driver.

"Seeing that your DIYer tool had detected speed sensor stored fault/codes, I doubt your problems are over with an Oxygen Sensor change.."

Arthur, if I was superstitious, I'd say 'ya jinxed me!'

But I'm just the opposite. What can I say except . . . you were right.

Yep. It came back today. Code 20 on emissions and code 9 on pin 14. Boy am I sick of this CEL saga.

So now the drama begins. We'll see how the dealer deals with this one. Perhaps I can find out (for free) if the fault is with the wheel speed sensor or the one behind the instrument panel.

Makes sense..
..anyway, I would mention that others are suspect of the speed sig from the dash b/c they will know where the test connector in the harness is for that.. then they can take an omh meter reading for verification..
You may also want to clear codes before going in so they can not claim you missed one .
Use the tool for pins 8 and 14 . You will know for sure that you have cleared b/c those both will come back with a single flash , indicating all codes have been cleared
The DM module [ CEL activator with built-in led/sw ] will not show a 1 code as it has to go through all drive cycle self -test before that can happen.
I have much more faith in Indies than I do in dealers...just for the guy to tell you an 02 sensor was going to rectify a No Speed signal code is nutz..
if I ever did that on this group, the lurkers would be on me like flies on s..t

PS


... just for kicks , give fuse 5 and 6 a spin in the fuse holder.. hall effect sensor [ B/6] power feed could be intermittant and would be picked up as No Speed Sig code.
.. these fuses look good , but don't conduct well sometimes ..

Well, the CEL is fixed. The dealer replaced the speed sensor located in the rear left wheel. I paid for the part, the dealer ate the labor. Interestingly, the cruise control still doesn't work!