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Discussion Starter · #1 ·
Hi
I hope I can get some help here.
I got the ESP wasrning light come on, turned the car off and on and it went away. car running perfect. after a while checkengine light came on, took it to autozone and they told me that its the oxygene sensor I replaced the upstream o2 sensors, reset and checkengine light came back on after 20 miles. took it to a certified Mercedes mechanic and his diagnose was a bad ecu. the car is running fine. very rarely it will stall ( it happened once). I am out of the 8/8 . I don't know what else this can be, I am having a hard time believing that it is a bad ecu since its rare that these will go bad please help
 

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Hi
I hope I can get some help here.
I got the ESP wasrning light come on, turned the car off and on and it went away. car running perfect. after a while checkengine light came on, took it to autozone and they told me that its the oxygene sensor I replaced the upstream o2 sensors, reset and checkengine light came back on after 20 miles. took it to a certified Mercedes mechanic and his diagnose was a bad ecu. the car is running fine. very rarely it will stall ( it happened once). I am out of the 8/8 . I don't know what else this can be, I am having a hard time believing that it is a bad ecu since its rare that these will go bad please help
I agree about getting a second opinion. Also, do a search on this site for weak battery as several of your symptoms are those of a weak battery. These cars need a near perfect battery and just because the battery is able to start the engine is not an accurate test of the quality of the battery. Have a conductive test done on the battery before you do anything else. If the battery has any weakness replace it then see what issues you have.
 

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Discussion Starter · #4 ·
I agree about getting a second opinion. Also, do a search on this site for weak battery as several of your symptoms are those of a weak battery. These cars need a near perfect battery and just because the battery is able to start the engine is not an accurate test of the quality of the battery. Have a conductive test done on the battery before you do anything else. If the battery has any weakness replace it then see what issues you have.

Hi I am planning to go for another opinion, but I am wondering what do you mean by conductive test? is that a normal battery test that autozone can do ? I believe the battery is fairly new, I am going to check what year it is but I think its about 1 year old
 

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Hi I am planning to go for another opinion, but I am wondering what do you mean by conductive test? is that a normal battery test that autozone can do ? I believe the battery is fairly new, I am going to check what year it is but I think its about 1 year old
Not sure if Autozone would have the tester. It is a fairly quick and easy test to do if the shop has the proper equipment. Many places only test for the current voltage or some type of load test. The conductive test determines if each of the plates in the battery can flow the full current at the rating of the battery. One weak plate and you can have issues with the battery.

If you do a search on this site you will find many stories of SLKs having all kinds of electrical gremlins from dash warning lights coming on, to false check engine light trouble codes, to the dash cluster and other components not working at all, and so on. In most all instances the car would start and seem to run without issue other than the gremlins.

So, when there are a couple of seemingly unrelated gremlins popping up, the first thing to check is the battery and the test must be good enough that a false positive won't be given (like just checking battery voltage).

For the record, I test every battery before I purchase it. More than once I have found a new battery that fails the conductive test. And, I have never bought one that passes the test that I have any issues with for many, many years. I maintain about a dozen cars plus several pieces of farm and construction equipment. I have tested a lot of batteries.

Good luck and let us know what you find.
 

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Discussion Starter · #7 ·
Not sure if Autozone would have the tester. It is a fairly quick and easy test to do if the shop has the proper equipment. Many places only test for the current voltage or some type of load test. The conductive test determines if each of the plates in the battery can flow the full current at the rating of the battery. One weak plate and you can have issues with the battery.

If you do a search on this site you will find many stories of SLKs having all kinds of electrical gremlins from dash warning lights coming on, to false check engine light trouble codes, to the dash cluster and other components not working at all, and so on. In most all instances the car would start and seem to run without issue other than the gremlins.

So, when there are a couple of seemingly unrelated gremlins popping up, the first thing to check is the battery and the test must be good enough that a false positive won't be given (like just checking battery voltage).

For the record, I test every battery before I purchase it. More than once I have found a new battery that fails the conductive test. And, I have never bought one that passes the test that I have any issues with for many, many years. I maintain about a dozen cars plus several pieces of farm and construction equipment. I have tested a lot of batteries.

Good luck and let us know what you find.
what equipment do I need to run that test. and where can I find instruction of how to do it ?
 

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what equipment do I need to run that test. and where can I find instruction of how to do it ?
Maybe this may help you understand the scientific basis: Why do Different Test Methods Provide Dissimilar Readings? ? Battery University

Conductive testing equipment are not cheap and unless you are maintaining a fleet of vehicles, it is probably not worth the purchase price . I would look for a local car battery dealer or reputable auto parts retailer that often sells car batteries, and ask them to see if they can do the test for you (usually they will do it for free, in the hope that you might purchase a car battery from them).

I got mine tested by an independent Interstate battery seller. Although mine was obvious that one cell may be failing because one of the side walls of the vehicle battery was starting to bulge out and deform slightly. Despite this the vehicle was running fine but I chose to replace the battery preemptively. The seller also tested the replacement battery before the install. The seller also gives you some money if you give them your old battery as the different minerals/metals can be recovered and recycled (this may vary from state to state).
 

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Discussion Starter · #10 ·
Hi guys a quick update
I have a 2007 slk280 , I went for a second opinion took the car to mercedes Benz dealership . After 2 hours of diagnostic they told me that they need to go more in detail and I have to kee the car . I did !
After two days , they came out with this :
Upstream o2 sensors both need to be replaced, I told them it's impossible since I replaced those 2 days ago. They basically told me we are not going to charge you and if it's not the sensors we don't know what's going on .
The car is running normal , they reseted the light , I left and it came back on after 17 miles :) the car is still running fine , good power and no roughness . Any ideas?
 

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Discussion Starter · #12 ·
That's puzzling. Did the MB dealer replace the O2 sensors that were only two days old?

Hi , when I took it to mercedes I didn't tell them what was previously wrong . I wanted another opinion . When they told me it's bad oxygene sensors, I told them that I just relaced them 2 days ago . I told them you are quoting me 1300$ to replace those and you are confirming that it will fix the problem but it won't because that's exactly what the other meecedes certified mechanic told me . I told them I don't trust neither you or the other mechanic . They told me that they won't charge me
 

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Discussion Starter · #13 ·
It's so puzzling that I think to get down to find what the real problem is , it will cost me more than the value of the car . The mechanic that said its a bad ecu advised me not to drive the car, well the car is still driving fine and I guess I will keep driving it until it fall apart. Any other option?
 

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What are the chances for 4 o2 sensors to go bad . The codes that the car is throwing are still saying the same bank 1 sensor 1 bank 2 sensor 1
When you replaced the two O2 sensors where did you source them and what make are they? I have had situations where generic O2 sensors were used and they caused issues.
 
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