I have been getting a intermittant check engine light . It came on yesterday and I took it to my mechanic, he used his scan tool to tell me that both rear oxygen sensors were showing to be a problem . He then said he needed to check the relay and voltage to them to make sure that they were the problem. I have 135000 kilometers (90000 miles) on the car and they are the original sensors. The o2 sensores from Mercedes are ridiculously expensive but I check the link above and 44 dollars for splice on sounds good. My question...can I buy a tool to get my own codes and would you recommend the universal splice on oxygen sensors and also do you think it is worth going back for further diagnostics or just replace them?[/align][/align]

 

Where are you located?What were the codes?usually the rear sensors read a stable line,if they are showing codes it is not usually them that is faulty,but items further upstream.What year and model?Before he does anything post those answers to the above questions and we can figure it out.
ohlord
pm me if you need more help.

 

I go with Ohlord response.
Model/Year? Service history?
Yes you can buy inexpensive scan tool dependent of make and model etc but local garages will often take a reading for you (for free) since the procedure is so straightforward and they hope to get your custom.
Always cancel any codes (after recording data) and determine whether they reappear.

Get second opinion on what the code means. Not its definition but what causes the code.
DTC Diagnostic codes do not identify what the cause of a fault is. But just what test / data parameter is wrong.
Interpretation of what is wrong from the DTC is the "clever" bit.

Strange just rear O2 sensors are bad. Its the front ones that do the work. So what voltage/waveform did the sensor give?
A little more info on when the CEL comes on, and goes off would be useful.

Although they may well work satisfactorily I do not recommend "universal" type O2 sensors. They give more "installation"problems than they are worth and often introduce new "spurious" codes because the MB circuitry doesn't like some aspect of their design/manufacture.

IMHO O2 sensors are changed needlessly in a large percentage of instances. its usually something else.

First step is to get the codes, clear them, determine if they reappear and report back. Don't get out your pocket book yet.

Stuart

 

Thanks guys, It is a 2000 E320 4matic . Vert little work done on the engine other then routine oil and filter changes that I have been doing on my own lately. I am using regular gas ,do you think that may be a problem? I have changed the plugs 6 months ago., I just purchased a OBD 11 reader and hope to try it tomorrow and get some code info. The mechanic cleared the codes a few days ago and the CEL came back on today after about forty miles of driving over a three day period, it has subsequently gone out again. I am also getting a brake linning warning which I intend on re and re tomorrow.

 

Use the correct fuel.
If you use a lower grade the Engine Management System has to significantly retard the ignition the prevent any knocking and consequent serious engine damage.
Any saving you make in the cost of gas will likely be offset by poorer miles per gallon and of course you will loose the edge on performabce also!

Gas (95RON) here in the UK is currently in the order of £1.03 per lire = £4.68 per Gallon Imp = 7.85 USD per USGallon!
Stuart

 

Yup,you gotta use preimum fuel,that alone can trip a light..
ohlord

 

Chiro,

Why are you using a lower grade fuel ?. I am sure MB recommends
premium grade fuel for your model.

I use premium fuel even on my 1991, 190E here in the US. It runs
perfect and no knocking.

Regards

Syed

 

Ok ..I'm being cheap using lower octane. I'll change that today and see what happens with the CEL.
I'm in Vancouver , BC Canada and shouldn't complain at $1.05 CDN per litre.

 

Thanks for all the help. I did not change O2 sensors but filled up with premium gas and CEL light has not come on all week...yes!!

 

Maybe the CEL is as a result of increased emmissions due in turn to the retarded ignition required to keep the engine safe.

stuart