sub oxygen sensor

[alunwill]

having removed the cat and sub oxygen sensors from my 1uz (it's fitted in a cobra) can anyone tell me what voltage the ECU needs to get for it to think that the cat is working properly and the error coe can be canceled. I've read 0.45 volts but not sure if this is correct.

thanks

al

 

[Bushwhacker]

Link them to the main O2 sensors.

 

[alunwill]

that's an interesting one. I can see the logic but doesn't the rear sensors basically run steady state and indicate the cat is OK.

 

[poorsupra]

intrigued to see this solution, going to turbo my 1uz, and would like to have them plugged in, and still have no CEL's.

 

[alunwill]

Just got hold of some info about lambda sensors.

Apparently the rear sub oxygen sensor is a check on the performance of the cat. It should have some oscillation between 0.4volts and 0.5 volts which is around the steady lambda state of 1 which is what the front sensors are trying to achieve but don't accurately do so, hence the need for the cat.

So, all I need to do is make a volts reference to give me around 0.45 volts and check the principle!

al

 

[George_R]

in vvti 1UZ's , if there's heater circuit error ECU won't check for the sub o2s signal
if you emulate heater, it assumes the cat is ok if sub o2s voltage don't exactly copy that of 1st sensor (per each bank), and at the same time crosses 0.4v towards 0 and 0.5v towards +inf . Threshold crossing take place upon shift from cruising to WOT or fuel cut (zero throttle, deceleration)

 

[lux project]

Interesting as I'm trying to clear the same fault code. So is there an easy fix, as it looks like throwing a resistor in the circuit wont be the answer?

 

[George_R]

throwing resistors will clear heater circuit codes, but wrong sensor signal error would pop up after a while. You should make some sort of emulator then. ECU checks for very basic things, if the voltage at sub 02 sensor input sometimes crosses 0.4 / 0.5 V threshold, and at the same time it does NOT copy main 02 sensor signal, ecu thinks everything's fine

 

[GhostRunner]

Depends on what year it is.
Mine which is a 1992 sc400/Celsiour
the subs are pyro sensors, not "02" sensors.
I have not measured them yet but will be...

 

[George_R]

I think it's ok then just to throw resistors of appropriate value. I doubt 1992 ECU is that smart to monitor the rate of change of cat's "temperature"

I would double check however that yours are not old fashioned 02 sensors that just lack the heater

 

[GhostRunner]

Hi George, I owe you one mate 4 your help before with wiring probs so only happy to help.
I could not believe it my self but the two sub sensors on mine are in fact thermo resistors.
When I removed them I seen that they are just a solid cylinder so I heated them in water and checked them with a multimeter.
Yep, resistance went down when they got hot.
Sorry, I do not know what range they are at about 500deg C.
I do know what a non heated sensor is like.
I have heard that on my setup, single wire primary sensors, they are usually "on" range or "off". The ecu does not care where they are. either high or low.
I will test this further but too much is getting in my way to finish my conversion atm.

 

[GhostRunner]

I salvaged them of a complete vehicle.
If I remember they were a grey and green wire opposite each other.
With the wiring diagram they were shown as heated. Mine did not have the heated circuit pinned.
The sensors have an earth return from the sensors body back to the e1 earth circuit.
I seem to remember that the range they were in is a "y" type thermo resistor.

 

[George_R]

testing may be as easy as putting one of your pyro sensors in place of a main 02 sensor then running the engine for a while keeping an ohm meter handy. Anyway you'll complete your conversion faster if you figure out the essensials and leave minor things for some future work.

 

[GhostRunner]

THX George,
Motor is in and running with a set of custom headers. No error codes as yet.
Main point is I do not have the front of the exhaust installed to the cat
It is the only thing apart from a few clearance issues with the headers and IFS.
These motors sure do sound so good when running. LOL
Photo's are coming of the post cat sensors.
Just waiting for the phone to sort itself out.

 

[GhostRunner]

Just got hold of some info about lambda sensors.

Apparently the rear sub oxygen sensor is a check on the performance of the cat. It should have some oscillation between 0.4volts and 0.5 volts which is around the steady lambda state of 1 which is what the front sensors are trying to achieve but don't accurately do so, hence the need for the cat.

So, all I need to do is make a volts reference to give me around 0.45 volts and check the principle!

al

I wonder if an in4001 1/4 watt diode facing from the primary 02 sensor would do?
It has around 1/2v drop.

ie; wire from ecu to secondary -------|<-------- onto primary 02 sensor output.

 

[alunwill]

Does anyone know if a 10K resistor to ground is an acceptable mod for not installing the secondary-oxygen sensors. Currently don't have them installed and revs are running around 1200rpm.

Regards



al

 

[George_R]

short answer is no
however the lack of sub o2 's can't cause high idle

 

[alunwill]

Hi,


many thanks for that. Any idea what will simulate the sub-0x sensor.

It's a 2 wire and the circuit looks as though it's acting as a variable resistor - current coming from the ECU to ground, which probably trims an op-amp or something inside the ECU to trigger that the cats working.

Sure I read somewhere on here that the sub-ox has an influence on revs and also could tip you into limp mode if not fitted.

Al

 

[George_R]

ah ok, I just have no experience with that old 1UZ's.
The ones I worked with were 4-wires only, and vast majority of them were JDM versions
non-vvti 1UZ ECU's seemed to be fine without anything: they didn't do anything really except throwing error codes