joe diego

iTrader: (3)

Anyone have the California ecu pinout for a 1992 SC300 5 speed?

I’m trying to wire in a 4 wire O2 sensor but there is already a wire going into B71.

Instead of using B71 is there an alternative?

The wire going into b48 is white, which correlates to color of the wire on the O2 sensor in bank 1 (closest to the radiator).

KahnBB6

iTrader: (5)

Actually I was just looking this over the other day and have the entry from my build thread handy:

https://www.clublexus.com/forums/bui...l#post10172400

That post will include cross-reference information to the USDM Supra MKIV Turbo's under-car 4-wire (heated) O2 sensor as well but I have the 92-94 SC300 Cali Spec wiring diagrams for that circuit listed there.

Only one problem with my notes: I never figured out precisely what Pin 2 of the 4-wire under-car O2 sensor connector went to exactly. So in my case I ended up building a patch extension harness to connect from the SC300's under car O2 sensor (for all Cali SC300's that's the #3 O2 sensor that is 4-wire heated) directly to the correct wires on my Supra 2JZGTE swap harness.

What I wanted to do was find *every* correct wire to go directly through the 2JZGTE harness to the SC body plugs... since any SC300 that is Cali-Emission spec already has the under-car O2 sensor wiring from the factory (the connector is inside the car on the side of the trans tunnel just below the radio on the driver's side of that tunnel when you lift up the carpet a bit-- you have to remove the center console from the car first). But since I never figured out for certain exactly where my connector pin 2 wire should go I reluctantly went with constructing the patch harness.

If you can use my notes in that post and find out exactly where that last O2 sensor pin connects to for certain in the SC300 wiring then you can wire right into the correct SC body plug pin locations and use the stock CA-Emission body wiring to that O2 sensor plug down below the radio on the side of the trans tunnel.

I don't know where "B71" or "B48" are located. I only know the diagrams below:

joe diego

iTrader: (3)

Thanks for this.

According to the diagram B71 is used for the sub O2 sensor for Cali cars (Wire color BR-W).

Since I’m using a jdm ecu I don’t think if depin this wire it would cause issues and I’ll just run a wire from my new 4 wire 02 senor to B71.


B71 wire cali ecu

Ali SC3

iTrader: (10)

With the jdm ecu, you really only need 1 heated o2 sensor connected to the right spot for the tt ecu (so that is ox1/ht1 or ox2/ht2 from the sc300 harness).
you have 2 main o2 sensors before the cat, and one of them should be wired to the right spot already for the tt ecu mod (i forget if its the front or back one, do a test and see which one works or has continuity)

the o2 sensor under the car, the jdm ecu does not have or use. you can disconnect this at the ecu along with the extra pre cat o2 sensor not being used.

In general for o2:
The pin that says OX1, OX2 etc.. that is the signal wire. that is the most important wire to connect. that is the output from the o2 sensor.

The HT wire on the ecu, which I think is the one you circled cause I can't read it, is for the ecu to turn the heater on. ecu will ground this pin to turn the heater on.
On some cars, where there is a 3 pin o2 sensor instead of a 4 pin, this wire is just grounded via the other ground wire so that the heater is always on when the car is on.
Most of the toyota's over here will have the 4 wire o2 sensor controlled by ecu.

The other wires are power (usually black/red or similar), and the last wire will be a regular chassis ground.

So if you are keeping your original California harness and doing the tt ecu mod... make sure the one o2 sensor you are using the signal wire (OX1 etc..) and the heater wire (HT1) are going to the right places for the tt ecu (which only has 1 pre cat o2 sensor).
It should be getting power and ground from the right spots already. really I think one of the main 2 sensors is already wired correctly if you have 4 wire o2 sensors (cali models).

For the extra o2 sensors you can disconnect them at the ecu (like the post cat one) by removing the ox and ht wires or unplug them at the sensor; and you can leave them physically installed if you like or take it all out.

When I was running the tt ecu mod, I just had one 4 wire heated o2 sensor in the downpipe for the ecu, and a wideband o2 sensor next to it for my gauge.
Remember on a gte the exhaust runs together and there is just one o2 sensor, and JDM stuff had no post cat sensor, at least for the non vvti stuff anyways.