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Mercedes oxygen sensor

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Jan 26, 2016, 7:19 PM

Post #1 of 3 (1108 views)
Mercedes oxygen sensor Sign In

1991 Mercedes 300TE 3.0 120,000 mi.

I am getting a fault code saying that the oxygen sensor has a bad ground. I have checked the entire exhaust system and cannot find an oxygen sensor. Where do I find the oxygen sensor the fault code is referring to?

Tom Greenleaf
Ultimate Carjunky / Moderator
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Jan 27, 2016, 1:57 AM

Post #2 of 3 (1099 views)
Re: Mercedes oxygen sensor Sign In

General info as I personally never equipped myself with special tools or info for full service on these cars. A couple local shops only worked on them if more than totally routine maintenance.
Just like you could have found on part look up where it thinks (says) it's located as said below. Some things to check are the wire(s) to it and if routing is touching anything rubbing thru or if wire into it has rusted off how clamped on. There will be a plug to check as well.
If you remove it to just look at the thing for debris, color high chance you'll break it or the manifold or pipe so watch out for that. I'm not alone but in a rust belt area and these cars are actually WORSE than average for dumb stuff so much as removing parts to check/replace an air filter can get in trouble with steel studs into alloy parts w 10mm nuts snap right off flush - a problem.
I'm not sure if a code trying tell you bad ground means too much or too little. Check grounds all over a car this old anyway even likely that exhaust system is grounded to body with a strap or two?
Can find parts on line as needed but totally suggest only real OE parts (clones are everywhere) as dealer parts can be insanely expensive but available.
Side note: an '87 300E was here, not mine to deal with in total but check out several things for what was a clean looking car junked because of a broken windshield so rusted unseen under molding was beyond possible repair vs value as parts - bummer,

"The Oxygen Sensor is located:
Under hood, passenger side, rear engine area, below exhaust manifold to exhaust pipe flange, mounted in exhaust pipe "
So even with this pre OBDII it can and will throw codes or a check engine icon. Doesn't mean the item it points to still but rather that circuit.

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jan 27, 2016, 3:21 AM

Post #3 of 3 (1093 views)
Re: Mercedes oxygen sensor Sign In

It only has one


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