View Full Version : Narrowband O2 sensor - testing on the VVTi

10-03-05, 18:33
Bad news all, was after some feedback on what the outcome was.

Car passed everything except the emissions :(

Took the car down to my garage and they put on the front cat ready for the MOT.

Had a ring this afternoon saying it had failed the MOT and was running REALLY rich..

Anyways, these dont make much sense to me, but here are the figures on the print out:

Fast Idle Test:

CO Limit = 0.30% VOL - ACTUAL VALUE = 9.25% VOL - FAIL
HC Limit = 200ppm VOL - ACTUAL VALUE = 189ppm VOL - PASS
"Funny symbol thing" Limit = 0.970 - 1.030 - ACTUAL VALUE = 0.748 - FAIL

Second Fast Idle Test:

CO Limit = 0.30% VOL - ACTUAL VALUE = 8.91% VOL - FAIL
HC Limit = 200ppm VOL - ACTUAL VALUE = 238ppm VOL - FAIL
"Funny symbol thing" Limit = 0.970 - 1.030 - ACTUAL VALUE = 0.755 - FAIL

Natural Idle Test:

CO Limit = 0.50% VOL - ACTUAL VALUE = 9.50% VOL - FAIL

They said CAT was hot enough etc etc...


Please, anyone got any idea on how or why this is happening? They harped on about it being too rich also..

10-03-05, 18:39
Check the labmda sensor... and change.... stick a multimeter across the OX1 pin in the disgnostic port in the engine bay and conect the neg to battery ground... should be about 0.7 volts... higher than that its reading rich and problem is elsewhere.. it its a low voltage.. then the probe is knackered...

check your vacuum hoses...

just an aside but my car ran rich cos I had an auto instrument cluster in a manual car...

search on running rich.. lods of stuff on here, as I had this happen to me...


10-03-05, 19:06
Will the car running too rich really cause these high readings, or is there something else at work here?

Going to try and check the 0X1 pin, pull ECU fuses, get tank of petrol then re-check the readings.

10-03-05, 19:08
Try putting your cats back in! :p

10-03-05, 20:35
Hmm, my 98 VVT-i I had idling and checked that 0x1 test. I had a stable reading of 0.0V Anyone know what this could mean please?

10-03-05, 22:34
thats running way too rich. i'll start with checking lamda sensor . :cry:

10-03-05, 23:13
How do I check that Lamda sensor my old mucker?

ie, where it is and how to test it?

Many Thanks,


11-03-05, 18:08
I think I have found the sensor mounted on the downpipe bit.. Does the whole mounting have to come off, or does the probe screw off or something, as its very arkward to get down there, and nuts are tight!

Ian C
11-03-05, 18:24
Ah, just spotted this after replying to your other thread. If you've got a VVTi and it's the same a others I've looked at, you got 0v at OX1 because you haven't actually got an OX1 pin in the diagnostics port so you were multimetering plastic... Why Toyota took it out I don't know... You'd have to check the signal wire off the O2 sensor by probing through the insulation, be it at the sensor or at the ECU (er, whichever bloody pin that is lol - VVTi's eh? :) )

And getting the O2 sensor out of the downpipe is one of the easiest jobs on the car :D


11-03-05, 18:26
Which wire off the sensor mate? There is more than one. And would it be the same test again? + probe on the wire, - on the neg?

Ian C
11-03-05, 18:38
Yep, same sensor. I don't know which wire it would be as the colours change across model variants. You'll have two grounds, a power supply for the heater circuit, and a sensor reading. That means two will be at 0v, one at battery voltage, and one between 0 and 1v, which is the one you want.

You can unplug the sensor from the loom (the plug is at the front of the engine, trace the wire) and multimeter the pins on the loom connector for continuity and voltage. Check continuity first with ground, you'll find two pins will have no resistance, those are your grounds. Then check the pins for voltages, one will have +12v (ignition on) or around +14v (engine running) - you may log a fault code running the engine with the O2 sensor unplugged, so don't panic if you do.

The pin that is neither positive or ground it the signal wire. That's the one to probe into. A safety pin wrapped around the multimeter probe is a good insulation probe, leaves a v small hole (in fingers too :mad: ).

And yes, negative goes on the batter ground, for voltage and continuity tests.


11-03-05, 19:03
Hi Ian,

Thanks for that.. You know you mentioned about testing the loom with the connector unplugged? Just wondering if the sensor is unplugged, why do I still need to do that safety pin thing, if I can put the probe into the connector..

Or am I not reading your reply right?


14-03-05, 01:13
Guys, I have removed the connection. Tested the wires with IGN on. Found the following:

4 Wires.

1 Wire is 12V feed - with NEG probe on battery.. Other 3 pins gave no readout.

2 wires gave reading of 11.4V and 1 wire gave reading of 10.4V with +POS probe on battery.

Any ideas which one is the sorsor wire, which I can tap into and test the O2 sensor reading?

14-03-05, 19:09
Anyone got any ideas on this please.. Kind of want to get it back on the road :(

14-03-05, 19:46
not sure want type of sensor is fitted to the supras or the colour code. but as a guide to a 4 wire sensor
red---power supply battery voltage+
white---negative from ecu (not ground)
black--- OUTPUT
but i'm sure someone will be round shortly to answer your question :rtfm:

Ian C
14-03-05, 19:50
Hi Ian,

Thanks for that.. You know you mentioned about testing the loom with the connector unplugged? Just wondering if the sensor is unplugged, why do I still need to do that safety pin thing, if I can put the probe into the connector..

Or am I not reading your reply right?


Because you can't unplug the sensor from it's power source and expect it to give a reading :) You can unplug the sensor to find which wire is which but to actually get the sensor reading you need it plugged in, up, and running.

OK, easiest way to do it:
With the ignition off and the cable unplugged, check for continuity (resistance), not voltage, between the pins on the loom plug and the battery negative terminal. Two will give 0 ohms and two won't. The two that do are your two grounds. Doesn't matter which way round the multimeter leads are for this test.

With the ignition on and the engine running and the O2 sensor plugged in, probe the two wires that aren't the ground with the positive lead, the negative lead again on the negative terminal of the battery. one will give battery voltage (should be about 14v with the engine running), and the other one is your O2 sensor signal. It *should* be between 0 and 1 volt.

In your case, hopefully it's sat below about 0.5v which means it's reporting a lean signal because it's buggered, and so the ECU is overfuelling to compensate.


PS additional, the signal wire is pin 3 of the O2 sensor plug. Although the wire colours are different, the pin positions are usually the same across Supra variants (unless it's the ABS ECU ffs) - so, it should be the circled one in the attached piccy...

15-03-05, 09:45
Ian, you are a diamond..

I will check this today matey..

Many Thanks,


17-03-05, 21:09
Ian, I have finally got around to doing this test.. Hope you can make a conclusion on the following results I got:

With the IGN off, I had 2 pins on the loom that outputted nothing in OMH, and 2 which outputted 56 and 0.5 I think it was..

So, I then took note of these two wires and connected the sensor back up. Proceeded to start the car up and then checked these two wires for voltage.

One provided me with a reading of 14.0V - Positive feed I am guessing
The other provided 0.0V

Any ideas on what this means now, and how to rectify?

Many Thanks,


P.s. Guessing sensor is either nacked or dirty and should be reporting 0.5V???
Only problem is damn sensor seems hard to get off, as I have no ramps etc :(

Ian C
18-03-05, 18:36
From the way it reads you found the two wires with 0 resistance to ground, i.e. the two earth wires, and then measured the voltage on them? That's not right, you need to measure the voltage on the *other* two wires, i.e. the ones that haven't got 0 ohms resistance to ground.

If that's the case, do the test again but on the other wires. If I've misread your post, then yes, you should get more than 0v but let the engine warm up a bit before coming to any conclusions, it takes a minute to get going from cold and you'll see the voltage climb as the sensor heats up and then the voltage will either fluctuate around 0.5 or settle at a different figure.


PS the sensor isn't hard to get off. You need a small ratchet with a 12mm (I think) socket on it and a weeny extension bar, and you can fit your arm down past the turbo James-Herriot-stylee and undo the two bolts holding it in place :thumbs: No other dismantlement is required, and no need to go under the car.

12-12-12, 08:14
Nice information guys.
I'll check my o2-sensor cause I'm running toooooo rich:(