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Category: Mercedes
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Merc 320E. Yellow light on dash that indicates a problem.

Customer Question

Merc 320E . Yellow light on dash that indicates a problem. Mechanic says it is the O2 device on exhaust that has failed. If correct what is the O2 device and what does it do. Can we continue to drive the car.
No mechanical problems come up on the dash instrument panel.
Submitted: 3 months ago.
Category: Mercedes
Expert:  reggiewhiddon replied 3 months ago.

Hello and thanks for the question. If i read it correctly your check engine light has illuminated you took it to a mechanic he pulled the codes, and tested and told you you needed an o2 sensor.

The 02 sensor and your car has 4 of them, they screw into your exhaust manifolds and there job is to measure the amount of oxygen in your exhaust, and report that to the computer, which uses that information to either richen or lean your fuel. Now if it fails the computer software goes into open loop where it runs off a base calculation, which keeps your car running but fuel economy and performance suffer. An 02 sensor has a life expectancy of about 100 to 150k miles as long as it lives in a healthy environment, meaning no skips in engine. It is important to note that there are two ways the sensor can flag a code one would be where it stops functioning as a sensor or starts reading slow the other would be if the heating element that is used to heat the sensor up fails or goes open, think of it like a heating element in your hot water heater, now if the code is due to a failed heater, and the sensor still functions otherwise you would have no idea other than the light being on. So to answer your question correctly i would like to know the code it has set,

Expert:  reggiewhiddon replied 3 months ago.

If it is the heating element i have seen the sensors run a long time, and the heating element failure could be due to a power loss such as a blown fuse or faulty relay. I hope i have helped you

Customer: replied 3 months ago.
Thanks Reggie,
unfortunately I do not have the code. The mechanic read the problem from the computer and after I booked in for a replacement sensor I noticed that the light went off and I cancelled the service. The light has come back after about 5 days. The car has done about 95,000 KM ( not sure on miles but about 70,000M)
Repairer had quoted $1650 ( about $2000 US) to replace the sensor. Seems a lot.
Is it a complicated job to replace the sensor.
Should I have it done immediately.
Customer: replied 3 months ago.
If it is a heating element failure due to a faulty fuse or faulty relay would this show up on the instrument panel as a fault.
Expert:  reggiewhiddon replied 3 months ago.

Yes sir if it was a heating element failure it would illuminate the light for that, your mileage is a little low for a sensor failure id bet your heating element failed. That seems like alot for a sensor i know over here in the states you could get them all four replaced for that and more.

Expert:  reggiewhiddon replied 3 months ago.

could you get a second opinion or there alot of shops close to you

Expert:  reggiewhiddon replied 3 months ago.

May i help you any further with this, if i have satisfied your question kindly give me a positive rating for it is how i receive credit for helping you, and please know any follow up is covered say if you want to get the code your setting and give it to me i will research it and advise you further. I thank you so much for using the service and your complete satisfaction is important to me

Customer: replied 3 months ago.
Unfortunately the authorised Merc dealers all are known here for inflated charge rates.
There was no mention of a heater element but I will have them recheck. Are all four sensors on the exhaust identical and if so I could possibly order the part on line from the US and have it installed. I understood that the labour time was not very long to do the job. What do you think??
Expert:  reggiewhiddon replied 3 months ago.

The labor time should be like 42 minutes and honestly you could do it yourself it just screws in and has a connector and on your car there not that bad to access, i would advise you to save yourself a ton, matter of fact you could buy all four and have money lots of money left over

Expert:  reggiewhiddon replied 3 months ago.

as for the four being identical i beleive the two front are the same and two rear are same, but i am not a parts man so dont quote me on that.

Expert:  reggiewhiddon replied 3 months ago.
Good morning sir just wanted to make sure I had answered your question and you were satisfied