pendrag

I was over at Autozone the other day asking about their lend a tool program. I wanted something to read my O2 sensors output. The guy said that it would take a static picture of their readout, but that it was inaccurate and he didn't recommend it.

Is that right? I'd like to see if my sensors need to be replaced.

James Woods

iTrader: (1)

If the sensors need replaced, they will usually have a code, if not, you need a scanner that has live data and you watch the voltage coming from the sensor as you drive the car and go from WOT to off throttle. If you have no experience reading live data of O2 sensors, you might not know how to tell if they are bad, it can be confusing of what they are supposed to do, they will usually always have output if they are bad or good. If there is no output you will for sure have a code.

BigBallsMcFalls

you need a toyota techstream to read the bank 1 sensor 1 air/fuel sensor levels
if you are looking for the mixture (methinks)
(99 is likely to have one)

obd=II can tell you if a/f or o2 is bad
obd=II can tell you the level readings from the bank 1 sensor 2 o2 sensor
obd=II could tell you level readings from bank 1 sensor 1 if it is an o2 sensor
obd=II cannot tell you level readings from bank 1 sensor 1 if it is an a/f.
you'll need a more advanced techstream or equivalent that can read the toyota ecu for an a/f.

xxxtreme22r

an o2 sensor can be bad and not throw a code, only time a bad o2 sensor will throw a code is if the ECU is not reading any output from the sensor itself. Now a bad o2 sensor can cause a cat efficiency check engine light though. If bank 1 sensor 1 is reading lean and ECU sends more fuel to richen and it richens enough it may throw a Bank 1 sensor 2 fault in the way of a cat efficiency because the cat cannot not process enough unburnt fuel through it. Same goes if the bank 1 sensor two is reading rich and is really not. That will also throw the cat code even though the cat is good.

All the ECU see's is voltage readings from the 02 sensors. A simple volt meter inline with one or two of the o2 sensor wires will tell you if it's reading lean, stoich or rich. Off-hand I don't know how to do it on the yotas, but I can tell you how to do it on a 92 BWM. Yes OBD 1 vs OBD2 but it's really all the same.

vital22re

iTrader: (2)

Find a Scanner that is capable of "live data"

BigBallsMcFalls

yes BUT

on a 99, the b1 sensor 1 is likely an a/f sensor. volt readings are useless, you
cannot accurately test it directly like you can with an o2 sensor (unless it is dead or dying).
you need to decode the amperage change waveform not the voltage change...that requires the ECU or an advanced
OBD=II tool

this doc is all about a/f and o2 and how toyota uses them

http://www.autoshop101.com/forms/h37.pdf

xxxtreme22r

read page 7 again, yes it's different from a regular o2 sensor, but it's still based on voltage. only your reference voltages change and are actually opposite of a regular narrow band 02 sensor. Taking voltages att the A/F sensor still works you just read the voltages different.

A/F is designed to give 0 current @ 3.3V. If rich then voltage will be below 3.3V, if lean the voltage will be above 3.3V.

Tricky thing with that though is the fact the current changes directions.

Edit oops wrote that wrong.

Anything below 3.3V will show on the volt meter as being negative voltage and anything above 3.3V will show as positive voltage.

BigBallsMcFalls

Ummm NO

sure you can read volts, but that doesn't tell you anything truly useful

you have to get the reading from an OBD=II that can convert it
or get it from the ECU. the volts will NOT tell you anything other than
lean or rich or 0...you need to read the -amps- and the waveform with
a special tool with an anolog to digital converter to obtain any real accuracy
with an a/f. read the whole thing

volts only do not work on an a/f. a/f is highly accurate but requires volts + amps reading,
and the amperage waveform passed to an anolog to digital converter, and calculations to convert it to a number.

xxxtreme22r

page 6 gives a diagram on voltage versus A/F ratio. And also page 7 goes on to say it's the current that cannot be measured accurately not the voltage.

Also says A/F sensor voltage is directly proportional to the to the 02 content.

4V will be an 18.5 A/F ratio
3V will be slightly less than 14 A/F ratio and again the volt meter will read that 3.0 as - 3.0v because of the direction of the current flow.

James Woods

iTrader: (1)

Im going to have to agree with XXXtreme, when using a scantool that does live data, I will choose to watch both the AF sensor (O2 sensor 1) and the second O2 sensor and put the data into graph form and from there when you go from WOT to off throttle you can watch the two O2 sensors mirror each other only opposites. A slow sensor will mirror the second O2 sensor only later and some will never dip into lean or never go to rich. This of course is all in voltage, a bad sensor can cause a false PO420 code for a cat and this is the reason why when I worked for Subaru, they required a 20 minute drive down the freeway while watching the live data because they had a problem with warrenty cat repairs, some people would replace the cat and the code would come right back from a bad O2 sensor.

xxxtreme22r

which brings me back to one of my original posts about getting a false cat efficiency CEL.

maui454

I have a program that does live scanning. It is call Proscan 5.0 and I bought a elm 327 usb scanner off of ebay. It works great. It is cool because it shows stuff like coolant temp oxygen sensor voltage and pretty much any sensor that is on your truck.