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2JZ-GE NAT B1S1 B2S1 merger. Confused!

276 Views 7 Replies 4 Participants Last post by  VegasIS3
Hi all,
Driver of the Angry Beamer Beating Beaver coming back at you with a interesting issues here.

been reading the crap out of the forums and am alittle confused coming to merging the upstream O2 sensors on my 03’ 5MT is300

I have the harness out right now and am wanting to splice the harness itself as when I took my exhaust off and scrapped the cats the b2s1 sensor was stripped and not coming off so I scrapped them with that.

when I went to scrap them I only got $20 as they were aftermarket cats:(

my issue is there are supposed to be 4 o2 sensors on the car. Mine only has 3. I’m thinking this has something to do with the aftermarket cats.

so anyways. I have the whole engine harness in my hand and i Have the plugs labeled but am confused.

What I thought was b2s1 is a different plug style then b1s1 and what ever my third plug would be? (I guess it would be b1s2 and b2s2 merged together) So b1s1 and b1s2 are the same plugs but b2s1 is different
Ill show pics below the give reference.

my question is what colour of the signal wire is in the harness for b1s1 and b2s1 and do I need to splice all 4 wires together or just the signals? I’ve read conflicting opinions about splicing only the signals or the heater wires as well.

I know the blue wire on the o2 sensor itself is supposed to be signal, which would make the Red and white striped wire on my harness the signal wire. But there is also a solid red wire as well as a brown(yellow looking) wire and the last one is another brown wire (pink looking)

the solid red wire and the brown/pink looking wire go into there own separate green shelled casing with a piece of bare wire in between it which tells me that one of those is probably signal because the stripped wire would be there to help fight interference.

on the second plug which I assume is b2s1 there is no hard shelling around any of the wires and the colours consist of solid brown, blue striped yellow, blue striped white, and pink striped blue.

on the last plug which I assume is the post Cat plugs or b1s2 and b2s2 splice together the plugs are solid black (with hard green shelling around it) black and red, light brown (but pink looking) and a darker brown.
for reference the signal wire on the o2 sensor itself goes to dark brown wire on the harness

I know this sounds so confusing but bare with me (wiring pun intended ;) )

And I’m saying the wire look like they are another colour because of the heat discolouration.

so which wires should I splice together?
Should I avoid this mess and just splice them together at the ECU side?
If so does someone have a pin out for that? I cannot find one anywhere. Any forum that I read on here that has one posted, the link is broken and takes me no where :(

im very confused and this is the last thing I need to do before I throw the motor in the car.

pics below for reference. If you made it this far in the post then you get a gold star!!!


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Picture 3 (FD127859-39DB-41....) is not of a connector for an O2 sensor. Rather, it appears to be TPS or APPS.

Also, the final/fourth O2 sensor is located pretty far downstream - under the rear passenger-side seat. As such, the engine harness does not have a pigtail for that sensor. Instead, it is part of the vehicle harness. You can get at it from under the back seat.
Okay that’s interesting. There is also one across on the other side of the head that I labeled as 1 and this other style of plug I have labeled as 2. Maybe that’s what’s confusing me? I just put the harness on the motor to help me understand it better and it wouldn’t make sense that the plug for the o2 would be on the other side of the motor.

I think I’m on to something here. I’ll post photos below for reference.
Thanks for the reply! Have you spliced your o2 sensors on your is300 then?


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I was running my o2 sensors merged with b2s1 actually connected to a sensor in the downpipe. What I found is that the fuel trims would start off the same for both banks, but after some driving miles, they would start to skew apart and eventually the ecu would need to be reset to clear the fuel trims as it would drive one bank very rich and one bank very lean because it was getting confused while making changes and seeing them on both banks with the merged o2 signals. I believe the most effective way to run the o2 sensors for turbo now is to install bungs on the actual turbo manifold in runner 1 and 6 and let the stock ecu see those 2 separate o2 sensors for the upstream. I've seen this work FAR better than an o2 merge with a local guy who has an NA-T setup on stock ecu as well. I plan to add these o2 bungs to my cx racing manifold when I put my built engine into the car.
Hmm okay I will keep that in mind. I’ve heard that as well but also heard that the merging can be off by alittle but still be in the safe park. How many miles of driving did you have to reset it? I’ve already wrapped all the headers and don’t have access to a welder anymore as I just quit my job 1 week ago.
Think I’m safe to run the merger until next summer when I go full stand alone?

Hello, I actually think you have asked me about this on my latest YT video. While the best way to go about tuning these cars is a stand alone hands down, I am still auto as are you I believe. Some will say don’t merge them and others have without much problems.

I have mine merged, just match wire for wire and merge them for the bank 1 & 2 UPSTREAM sensors. As far as the downstream sensors, I don’t plan on merging them but rather building sims for them. Mine are currently just plugged in and hanging which is NOT a solution but I’ve only driven the car around a handful of times. I will build sims for them and they will just stay plugged up to satisfy the heater circuit only.
is that you Knownworldwide? If so FANTASTIC VIDEO SERIES BROTHER! You have been so helpful I cant Even begin to thank you.
If not then I’m not sure if you have the right guy, but I appreciate the comment on the thread.

I have a new question for you. Any idea if you remember the size of the turbo oil feed adapter for the CX racing GT35 turbo? I had one in my kit but lost it when pulling the motor.
cx racing says on their site from what I can gather that it’s a m12 x 1.0mm thread in the turbo to a 4an for the turbo feed line, which sounds correct but on the site they only offer one with a restrictor valve in the adapter itself. Well while looking into my turbo I can see it already has one and I worry running two will ruin the turbo!!
Any idea? I don’t remember the one in the kit having a restrictor in it?
I’ll show a photo for reference, if anyone else has any clue on this please chime in!! I’m so close!
Thanks all!


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