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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3567
Experience:  Qualified Mercedes Benz Diagnostic Technician - 20+ years experience - Workshop Foreman for Mercedes
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1996 Benz C-280 Approx 230k mileage About 3 weeks ago 2

Customer Question

1996 Benz C-280
Approx 230k mileageAbout 3 weeks ago 2 issues happened.
1-The Speedometer dropped off indicated 0 speed even while driving. The following lights also illuminated: PARK BRAKE LIGHT, DISC BRAKE. At first these would illuminate…then a few minutes while driving the speed indication would come back, and the associated brake lights would extinguish. After about a week the lights remain permanently illuminated.
2-Around this time, I noticed a rough idle, slow acceleration and lack of power going up hills.
Here is what I’ve done to attempt to correct:
1-Regarding the brake lights, I recalled my last brake service entailed replacement of the front brakes. I took the car to a local shop and they looked at the rear brakes and told me the pads were worn and a rotor cracked. So, I had the rear brake pads and rotors replaced. However, the brake lights on the dash remain illuminated, and I don’t get a speedometer signal.
2-Regarding the idle/power problem, I put in some fuel injector cleaner (like STP) but that didn’t solve things. I also replaced the following:
a-Mass Airflow Sensor
b-Spark Plugs
c-Spark Plug wires
d-Spark Plug boots (but not ignition coils)This has still not solved the ugly idle problem, power problem nor restored speedometer and extinguish lights.
I took the car in today to a local shop to have the diagnostics of engine taken. After two different diagnostic machines, couldn’t get a connection between their machine (snap-on) and the car. They finally told me since the check engine light is not on in the car, there would not be any diagnostic codes to be read.
I am now ready to try something new, but didn’t want to blindly put more $$ into a action that is not going to solve the problem.
I am contemplating getting new ignition coil(s) but don’t know that this will solve the problem.
*** of note, when I do run the car I do detect a smell of gas that was not present earlier…but have not searched for a leak. **
Submitted: 10 days ago.
Category: Mercedes
Expert:  Eurocar Inc replied 10 days ago.

Thanks for choosing Just Answer . I'm Wolfgang here to help!!

I am confident we can resolve your problem together. Please
understand that I don't know your skill level. In most cases when you have a problem
with the way the vehicle performs, specialized tooling is required to acquire computer
data/information or engine testing results. We didn’t build these complicated vehicles; we
just diagnose and fix them. Also understand that I can't see, smell, hear, or touch the
vehicle either, so it may take a few replies to get to satisfactory results. Note there may be an issue where the complexity of the issue will require a Premium Service. This service will be an addition to the normal question cost. Usually it does not come down to this but keep in mind!! I am also going to direct you with the fastest, easiest and most common things to check first. Please be
patient and permit me to do what I do best.
I also try to give all of the information you may need, expecting a “positive rating” in
return. I will also continue assisting you after you have rated me, if necessary. If there
is any reason I cannot get a positive rating, please let me know why “in advance”, so I
can go another direction for you. I am sorry you’re having this problem; I’ll help you
through it.
Below is my first answer or request for more information. If you do not understand it, or you need more information from me, or need me to go in more detail.

on your issue you will need a scan from MB with the factory scan tool . best educated guess you have an issue with the sam module for the instrumentation / speedo issue . without the scan there can be many possibilities too much that checking everything may take a long time . need to narrow this down .