oxygen sensor wiring

[blakeg]

just about to go wire up my four wire oxygen sensor, (as my car is only a single wire)

reason being, my sensor has been moved to the s2 postion, and needs a heater to work effectivly now,


Stock Toyota 4 wire
can anyone confirm if this is correct
Black -Heat (+12vdc)
Black-Heat (-12vdc)
Blue-Signal (ie connect to my original wire)
White-earth (connect to chassis)
__________________

so i dont blow it up

[blakeg]

anyone.... so despreate.

[cambelt]

Yes thats it except the white goes to E2 of engine wiring sensor earth
Dave

[timbosaurus]

Yeah, and technically there isn't a -12V... it's just ground.

Black - O2 heater circuit ground
Black - O2 heater circuit 12V
White - Sensor circuit ground wire
Blue - Sensor circuit signal wire

[blakeg]

so with white i can just ground out
to the body, or it has to go to a specific negative

remembering the car is just a one wire from the factory

[timbosaurus]

Yeah, there's no harm in doing that.

The 1-wire sensor just grounds through the O2 sensor body anyway, but they changed to a 2-wire (with an isolated sensor housing) to avoid relying on grounding through a potentially dirty/corroded thread on the sensor.

[oldcorollas]

it is better to ground it to the earth that is used for the ECU, because the signal is small (0-1V) and any difference in voltage between your choice of ground and the ECU's ground, will result in an incorrect reading.

you want the ECU to have the best reference possible, and 0.1 or 0.2V out is far too big for it to work properly

yes chassis could work, but you may as well as least extend the wire to go to the point of chassis where the ECU grounds..

[timbosaurus]

Then the 4-wire adds a heater element. There was also a 3-wire that didn't have an isolated case and grounded through the case.

[timbosaurus]

it is better to ground it to the earth that is used for the ECU, because the signal is small (0-1V) and any difference in voltage between your choice of ground and the ECU's ground, will result in an incorrect reading.

you want the ECU to have the best reference possible, and 0.1 or 0.2V out is far too big for it to work properly

yes chassis could work, but you may as well as least extend the wire to go to the point of chassis where the ECU grounds..

Yeah, it would be worth the effort.

[blakeg]

ok
i got plenty of grounding cables going back to the battery, it would be best to come off one of those, as frankly i have nfi where the ecu grounds

[blakeg]

ok finished now, turned out the signal wire had an integrated earth sheath, so i used that as my sensor ground,

for the power i was under the impression that i could just tap into the alternators on wires with a fuse would be fine, however the battery check light is now on still charging correctly

but overall good as the engine is now not running uber rich now, but only time will tell if my economy will return

anyone suggest a better place to tap in ?

[TERRA Operative]

Does the heater stay on all the time normally, or is it only on long enough for the o2 sensor to heat up?

If it's on all the time, couldn't you just wire the heater to the ignition, via a relay?

[blakeg]

all the time as far as i am aware,

yes i could do that, looks like the path i will be taking, but it is such a small load (12w) i did not think there would be an issue

[timbosaurus]

That's about 1 amp, which isn't insignificant, but shouldn't need a relay.

Obviously if you run it direct from the alternator or battery, then you will want to run a fuse.

To keep it neat, I probably would have run 4 new dedicated wires to the ECU rather than one to the old connector, one to the chassis, one to the ignition, and another to the chassis. You could just tap all the wires into the loom at the same spot.

The heater power to the Ignition input of the ECU, and the heater ground to the the ECU gnd.

The signal to the signal wire, and the signal ground to the ECU signal ground.

But, there are many ways to skin a cat and the important thing is that your is working now

[blakeg]

well i will have to resolve the battery light being on, but i am sure il will sort it out,

does anyone know where the s2 gets the oxy sensors power from \

[oldcorollas]

as far as i am aware, the sensors draw betwee 2 and 4 amps during heating, and then 1 amp continouous when hot.
I ran mine off a relay triggered by Fuel pump power, which was controlled by ECU.

is it 3 wire, or 4 wire? if it had 3 wires plus sheath, then it is just a 3wire....

the integrated sheath is usually just a noise shield, similar to what is used for CAS and other sensors, to protect them from noise. does the sheath earth to the sensor body?

i would advise running the heater ground direct to battery or body, and keeping away from the ECU earth (or is there differet "earth" and "signal earth" ont he ECU?. kinda defeats the purpose of having signal wires grounded there, and then pumping 1 or 4 amps there with a heater..
I would advise using power from fuel pump to flick a relay... cos then the ECU can be energised for a long time and not burn out the heater.. it will onyl be on when the fuel pump is on.. ie, running.
i ran heater power to a good chassis ground, and the signal earth to the (megasuirts) ground..
i also had sheilded wire, grounded at one end (for all sensors)