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Discussion Starter #1
Hi I'm working on my '95 900SE CV, and it appears that the rear oxygen sensor was sheared when someone attempted to remove it and I can't find the wires in the harness that it should plug into. Hopefully I can remove the remains of the sensor with a reverse threaded bolt remover, but I can't seem to find the connector to plug in a new oxygen sensor. Do you guys know where or have a good picture of the location of the rear oxygen sensor in the Trionic 5 wiring harness?
Thanks in advance!
 

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A '95 may not have catalyst diagnostics, but if yours does both O2 sensor connectors are in the same place, by the thermostat. Is your CEL on?
 

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Discussion Starter #3
That actually makes a lot of sense. There is no third connector in the wiring housing thing by the thermostat. It does throw a CEL with a rear oxygen sensor error code, but the ECU is T5.5.
 

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T5.5 can come in several flavors, including with or without a second O2 sensor ("catalyst diagnostics"). If it's throwing a code, it's enabled. Only thing you can do now start digging through the harness. It originates at terminals 70 (signal), 51 (heater) and 47 (reference ground) at the ECM connector.
 

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Discussion Starter #5
Thanks for the responses. If the harness doesn’t have a rear oxygen sensor connector, will the connections for the rear heater and sensor be empty on the big ECU connector? If so, can I solder on my own wires inside the ECU? (I’ve already soldered on some of my own for programming it) Thanks again!
 

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If you have a broken sensor and a CEL for that sensor, it sure sounds like someone broke something. You're gonna have to do some detective work.
 

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Discussion Starter #7
Ok: upon further inspection, the wiring harness is missing wires for pin 70 (rear O2 sense) and pin 51 (rear O2 heat). But there is a bung welded to the rear of the catalyst and what looks like the remains of an O2 sensor in it... that confused me a bunch. I guess a replacement down pipe was installed at some point with the extra bung.

Anyway, I think to pass inspection it’s going to need catalyst diagnostics, so how difficult is it to add a contact to the wiring harness connector? Thanks
 

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Is your Check Engine light on?


If you are somewhere (like USA) where auto parts stores will read ODB codes for free, have them attach the reader to your car.


If it's an ODB-II car, it will connect. It should also give code(s) for rear O2 sensor (no signal, no preheat, etc.) If it's an ODB-I car, then it won't connect.


Check with your emissions testing place. Given your VIN, they should be able to tell you if they use and ODB reader, or actually put the car on a treadmill or do some other kind of actual exhaust gas test.


Last my my 1997 was tested, even though it's an ODB-II car for sure, the regs said tailpipe test for that model/year. It passed with flying colours. That of course was before the ignition-related misfire damaged the catalyst, after which it gave P0455 (I think) every week or two.
 

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Anyway, I think to pass inspection it’s going to need catalyst diagnostics, so how difficult is it to add a contact to the wiring harness connector? Thanks
If the car didn't have a rear O2 sensor from the factory, I don't see how they could require one to pass an emissions test. They should be able to look up what a given car was equipped with from the factory.
 

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A cheap OBD2 scanner will show "readiness monitors". If yours is not set up for a catalyst monitor the OBD2 scanner will show "Not Available or NA" instead of "Incomplete". Engine doesn't matter, it all comes down to the ECU the vehicle is mated with. In CT a car your age can have 2 monitors not set in order to pass emissions anyways, so no CEL and you should be good.
 

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Putting your location in your profile (along with your vehicle info while you are there) would be a big help.



1995 is pre OBDII. Few states would test such a car via the OBD connector. More likely it would be tailpipe output. But, as others have said, read your local regulations to see what/how they test and how many monitors you can have "not ready".
 
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