JoeSuff Posted February 18, 2017 Share Posted February 18, 2017 90 LS400 64k miles. Service engine (code 25) and Trac light on. Previously when I bought the car I had a small leak at the rear cat flanges to exhaust pipes. An exhaust only custom shop cut and replaced the bad metal. I was hoping having the offending pipes replaced would fix the service engine since it was right between the two sensors on both sides. I reset the lights but they came back. I purchased a set of NTK o2 Sensor (for some reason i thought the were OEM got them confused with the Denso) When I went to install the sensors I was unable to seat the replacement plug into the engine harness. I pulled them and saw the seperator difference. I can't see into the harness on the engine but it's the only thing that seems to make it so I can't seat the electrical part. Neither sensor was able to click into the harness but the both screwed in. I put the original sensor back in with no problem.I called rock and they said ALL including Denso have the same (+) like style connector and not the (-) like I pulled. I'll buy OEM if I have too But at 3x's the cost I don't wanna spend the money to have to splice harnesses.Anyone else ever have issue? Quote Link to comment Share on other sites More sharing options...
Exhaustgases Posted February 18, 2017 Share Posted February 18, 2017 Its been awhile since replacing the O2 sensor for me so I don't remember the plug. So either the tab deal broke off in your other end. Or they are using a different part or mixed things up and that is for a different year. I don't know. 1 Quote Link to comment Share on other sites More sharing options...
JoeSuff Posted February 21, 2017 Author Share Posted February 21, 2017 Well i was home for the day. Thought id try and snap a pic of the engine harness for the o2 sensor, ponder what i could do before dropping $150 for the OE part. I started with the passenger upstream since that was the easiest to see. Once i had the harness off i thought id give a go mounting the NTK sensors once again, armed with the knowledge that Rock and no sites i posted to seemed to have any knowledge of problems. ^^Mr Bob Exhaust Gasses being the only person to offer any personal input. I'm guessing that the car so old most people have abandoned following. Anyway with a lot of persistent wiggling and the help of a set of long reach bent nose pliers i was able force and finally seat the replacement sensor. Of course then i had to unclip it, pull out the threaded original and then insert the aftermarket once more. Im on my 4th restart and 35 miles. The light hasn't cycled on (yet) . If i get to 100 miles im hoping ill be okay. Incase any other First Gens should follow heres a few pics of the Upstream o2 Sensor connection Quote Link to comment Share on other sites More sharing options...
JoeSuff Posted February 26, 2017 Author Share Posted February 26, 2017 Update: All's good, Got to 111 miles on the new sensor and no eng light resurfaced. I decided to do the Downstream o2's this weekend. Read a couple threads where best practice would be to to have them all done together. I'm assuming the holes in my exhaust causes the o2 failure to being with. I used a set of Denso this time since it looks like everything from underneath the car is a Denso part. Quote Link to comment Share on other sites More sharing options...
sha4000 Posted February 26, 2017 Share Posted February 26, 2017 Downstream sensors have no effect on gas mileage. They are strictly their as a tell tale for emission purposes. 1 Quote Link to comment Share on other sites More sharing options...
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