How to test O2 sensor
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LittleCaesar
New member
If it is throwing the code for sensor and said sensor is original, I'd assume that the sensor is bad.
Get a scanner or app that shows live data. There is a subsection that shows O2 sensor values.
Get a scanner or app that shows live data. There is a subsection that shows O2 sensor values.
JayRolla
New member
Plug into the harness. Turn on your scanner and check the code. This will tell you if its bad. Ohh wait you did that already?
jeremyc74
Banned
What code are you getting? There are two different ones for the O2s. You can get a A/F ratio code, or a heater circuit. If it's the heater circuit code just make sure the wiring isn't broke and replace the sensor. Those are really the only two things that cause it. You can test the heater circuit with a multi-meter if you really want to waste your time.
If it's the A/F ratio it could be other things, but chances are it's the sensor. You need to hook up a scanner and monitor it to figure it out. Is it the pre-cat sensor, or post cat?
Also, I notice you're in CA. Make sure you get the right sensor. CA trucks have different O2s from the federalized vehicles. More expensive of course.
If it's the A/F ratio it could be other things, but chances are it's the sensor. You need to hook up a scanner and monitor it to figure it out. Is it the pre-cat sensor, or post cat?
Also, I notice you're in CA. Make sure you get the right sensor. CA trucks have different O2s from the federalized vehicles. More expensive of course.
Road Bull
Senior Member
Hrmm.. my oem sensor from amazon ran around $53-54 via prime.
jeremyc74
Banned
Depends on whether it's the upstream sensor or downstream, and CA emissions or not. Downstream for CA is about $40 and upstream is about $85 if you get the Denso sensors. Denso is the OEM and people have had trouble with other brands on these trucks so I'd stick with those.
There are a lot of different configurations for these depending on the transmission and emissions ratings. Rock Auto is a pretty good place to start.
Here's the upstream for a CA emissions truck with an Auto
http://www.amazon.com/Denso-234-900...6369630&sr=8-3&keywords=4runner+oxygen+sensor
LittleCaesar
New member
Oh, the infamous po420. As Jeremy said it could be the A/F sensor if you have two kitties or it may be the kitties themselves.
I'll let past posts speak:
http://www.toyota-4runner.org/3rd-gen-t4rs/99732-p0420-cat-converter-vs-02-sensor.html
I'll let past posts speak:
http://www.toyota-4runner.org/3rd-gen-t4rs/99732-p0420-cat-converter-vs-02-sensor.html
4Reak Show
New member
P0420
This generally indicates a Cat problem, not an 02 problem. Issue is, you're gonna wish you only had to spend $80 on an 02.... Here's the story: the ECU monitors the REAR 02 sensor (yes 02, NOT AFR for the rear) and wants to essentially see a steady voltage of around .7 or so with little to no fluctuations. Once it sees the fluctuations, it flags the Cat (p0420) trusting the 02 entirely. I've seen it happen when 02's die, and they normally die LEAN, meaning they would be registering little to no activity around .1 volts or so. This is also unpleasant to the ECU and it could flag it for the dead sensor as well, once again fully trusting what it is seeing. If you don't have a graphing scanner or graphing multimeter, then your options are only to throw a REAR 02 at it (and yes, occasionally this may fix it) and clear the code seeing if it comes back on.
The reason you need a graphing meter to check is because a basic digitally displayed voltmeter won't give you up to date responses. Instead they take an average value and display it accordingly, resulting in inaccurate live data.
The likely cure will be a Cat, but I would rather try an 02 myself anyway before tossing a few hundred or more at a Cat depending on how you replace it.
Good luck and let us know what you find.
I can give you more in depth testing procedures if you happen to have access to a graphing meter or graphing scanner.
This generally indicates a Cat problem, not an 02 problem. Issue is, you're gonna wish you only had to spend $80 on an 02.... Here's the story: the ECU monitors the REAR 02 sensor (yes 02, NOT AFR for the rear) and wants to essentially see a steady voltage of around .7 or so with little to no fluctuations. Once it sees the fluctuations, it flags the Cat (p0420) trusting the 02 entirely. I've seen it happen when 02's die, and they normally die LEAN, meaning they would be registering little to no activity around .1 volts or so. This is also unpleasant to the ECU and it could flag it for the dead sensor as well, once again fully trusting what it is seeing. If you don't have a graphing scanner or graphing multimeter, then your options are only to throw a REAR 02 at it (and yes, occasionally this may fix it) and clear the code seeing if it comes back on.
The reason you need a graphing meter to check is because a basic digitally displayed voltmeter won't give you up to date responses. Instead they take an average value and display it accordingly, resulting in inaccurate live data.
The likely cure will be a Cat, but I would rather try an 02 myself anyway before tossing a few hundred or more at a Cat depending on how you replace it.
Good luck and let us know what you find.
I can give you more in depth testing procedures if you happen to have access to a graphing meter or graphing scanner.
