Changing Oxygen Sensors 98 ML320 - PeachParts Mercedes-Benz Forum

ezra442 · #1 10-06-2003, 04:55 PM

I understand there are 4 O2 sensors that should be changed at around 100k miles on a 1998 ML320. Has anyone done this? Any advice? I understand there are sensors before and after the catalyst, but haven't yet looked underneath to find them. Are they hard to find and replace? Special tools?

Any help would be much appreciated!

djeep · #2 10-07-2003, 10:02 AM

I had to change a rear sensor. It isn't really all that bad other than the fact that it is really tight to get your hands in there.
There are 2 little clips that hold the connector in that I broke off, but 2 wireties later and all is good.
Once you climb under there you will see that it is really straight forward.
HTH
Doug

ezra442 · #3 10-07-2003, 11:11 AM

Thanks very much for your reply. I did get under there last night and looked around, and you're right. It's tight and awkward but very straightforward. I was able to get a wrench on all four of them. It looks like disconnecting/reconnecting the wires will be the toughest part.

The OBD II scan said that there are two bad sensors, Bank 1 sensor 2, and Bank 2 sensor 1. Does anyone know which ones this refers to? I'll probably go ahead and change all four anyway, since it does have 95k miles on it.

I did the sparkplugs last week. Another exercise in awkward and tight, but ultimately doable. I think the O2 sensors will be easier.

Gilly · #4 10-07-2003, 05:08 PM

Sensor 1 is a front sensor on either side, sensor 2 is the rear sensor on either side.
Bank 1 is the passengers side (right side), Bank 2 is the drivers side (left side).

Gilly

djeep · #5 10-07-2003, 05:33 PM

If you got through changing the plugs fine then changing the o2's will be a cake walk!!

What a pain!!
Like I said I broke the clips that holds the plug together, but if you put a small wiretie on the plug and another on where it plugs into and loop the wireties one through another it will hold the plug fine. Hope that made sense:p
When I did my rear o2 all I knew was that I had a rear o2 sensor that was bad, but didn't know which side. I figured that I would do one and if the code came back then I did the wrong one and would put the other o2 in that spot. I would spring for 2 new ones but at over $100 a pop I will use them until they are definately bad.
Thanks for the info Gilly, are the o2's the same front and rear??
And also is there a mid model change for the o2's or anything weird like that??
Thanks
Doug

Gilly · #6 10-07-2003, 08:33 PM

Doug:
The front and rear I believe are different styles. The other problem is that the harnesses (pigtail wires on the sensors) are different lengths also.

Gilly

PS the sensors are made by Bosch, you may find a better price on them for the same exact part by trying to find a parts outlet that sells Bosch brand O2 sensors. You may even be able to buy them locally, although they may need to be ordered. may save quite a bit over MB prices.

ezra442 · #7 10-08-2003, 11:47 AM

I went to a local autoparts store, and they wanted $175 apiece, just like the dealer, and had to order them. But I went online and found several sources that would sell them for $86-$92, with free shipping. These are all the Bosch sensors.

ezra442 · #8 10-14-2003, 12:55 PM

Here's how it all turned out. I ordered the sensors online, passenger side rear and driver side front. Cost was about $90 each. I got them overnighted to me for $20. Still a huge savings over the dealer.

I installed them myself. The passenger side wasn't bad at all--took about 15 minutes. The hardest part was undoing the clip that held the wires together.

The driver side front wasn't quite as easy. I could get a wrench on the sensor, but again, had trouble getting to the clips that hold the wire fittings. I wound up taking off the inner fender liner, and getting to the sensor from the wheel well. So it took me about 45 minutes to do that one. It would have been less if I'd just taken the fender liner out right away. It isn't hard to do at all, and it goes back together without a problem. All in all, though, it was way more awkward than it needed to be, just because of the wiring clips.

The old sensors had a gray oil residue on them which is why they went bad, probably--not a good sign. The thing has 96k on it. So I took it down to the Toyota dealer and took a bath trading it in on a new Highlander. I've had enough!