SL320 M104.991 O2 Sensor how to change?

[bgalakazam]

Benzworld is still thinking about it. I am a bit stumped. Bought a 1995 (May build) SL320 Euro spec Special Edition (often misnomered Mille Miglia) WDB1290631F121944. I have an upstream O2 sensor fault that keeps coming back.

pin: 4, blinks: 11, code: O2S 1 heater (before TWC) - Current too high/low or short circuit.
pin: 4, blinks: 13, code: O2S (Lambda) control system operating at rich or lean limit

I am going over deferred maintenance and O2 sensors were on the list anyway.

Checked on WIS, countless searches in English and German. I can't find where the sensor terminates. Looks like it might be inside the car in passenger footwell under carpeting like some 300E/E320. I failed at removing the carpeting, looks like I have to take half the car apart. Help with that if that is needed as well.


WIS is useless here:



Can any of you gurus give advice? I am limited in working on car in the narrow street I live in Germany right now so can't even jack it up. I can rent a lift on base, but rather have the cable ends identified AND the correct part to buy before I go in.

 

[gsxr]

Assuming the photo of that sensor is from your car (not borrowed from the internet), then yes, it appears the connector is inside the car hidden behind carpet and/or other stuff. If that is not your photo, you'll need to get underneath and check.

EPC shows 2 different part numbers for the O2 sensor, one has a round connector that attaches outside/underneath the car like the 400E/500E, the other sensor appears to be the internal-connection type with rubber grommet to pass through the chassis. It appears your car would use the early style (A0005402417) with the round 500E-style connector underneath the car - if so, no need to pull carpet out.

 

[bgalakazam]

My photo. It really looks like the cable goes inside, no way that is the socket. I’ll be doing transmission fluid change in the coming weeks on a lift and can get a better look.

Whats the easiest way to lift carpet? It’s one big piece. Take center console trim and peel from left side?

 

[gsxr]

Yup, that does look like the goes to a connector inside. But it also doesn't look factory.

Good question on the carpet - I have no idea. Need some R129 owners to chime in...

 

[bgalakazam]

According to this photo from my R129 build history book, it looks like O2 sensor goes in (despite being V8 model):



But next page shows the newer connector:



I'll just remove the trim and try to peel carpet away. Have to check 4/5th gear switch too. It's 4 C this week here, lovely weather...

 

[bgalakazam]

Figured it out! O2 goes inside cabin. However, a previous owner/mechanic spliced the wires, so I lost the other end of the connector. I'll need to use the clips or solder, but can get away with a ~$40 sensor that's not terminated.






O2 White --- Black Car
O2 White --- Yellow Car
O2 Black --- Yellow/White Car
O2 Gray/Yellow --- Brown Car



I fixed the connection after verifying with multimeter which are the heater wires. Cleared code did not come back. Ill still replace the sensor, but at least its connected right.