SnoViking

ok.... i got a PO420 code.. which i know... its either an O2 sensor, or the cat.... but thats where i run into a problem.... heres what i got so far.... i went to this site which i was referred to... http://www.obd-codes.com/trouble_cod...old-bank-1.php .... now at the bottom.. it goes as follows -
"Next step is to measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). The voltage should be low and steady (~200mV, depends on the vehicle). If the voltage varies (e.g. 100mV to 600mV) then it's time to replace the catalytic converter. In fact, it would be a good idea to test each oxygen O2 sensor while you're at it."

now the part i highlighted is where i think im missing something.... if it doesnt vary, does that mean that the O2 sensor is bad? or just that the cat is not bad... and which wires do I test... now im a motorcycle mechanic and if i got a book that told me to test the wires without tellign me which one.. id throw the book out the window... theres a black, blue and white wires... now do toyotas use a black ground or white? and if so, do I then test the blue wire? and no where does it tell me how to test the O2 sensor? can someone read the service manual and see if theres a test for the O2 sensor? it woudl be great... im going nuts here and I dont want to buy a $115 O2 sensor or a $90 cat if i dont know which one i need!!!


pat

Fink

Try a search, I think there was a thread started recently that dealt with this.

Fink

SnoViking

lol.. i think it was mine before too... the one where i got the website from....

JamesD

I think 420 is an EVAP code. I think it means it has a leak.

James

SnoViking

what has a leak? now heres the other thing.... the code first popped up right after... i mean within 5 miles of replacing the PCV valve... is this just a wierd thing or could the PCV valve be causing this...?????

SnoViking

if it was the O2 sensor bad... wouldnt i throw a PO133 code? not the PO420? Im going nuts here!

JamesD

Actaully you were right. Code stands for Catalyst System Efficiency below Threshold. Two things it can be. It can be a convertor or the O2 sensor AFTER the cat. How many miles on your rig? The PCV shouldn't cause that code unless the hose came off of the PCV. Usually from what I have come across is the rear O2 getting worn out.

James

JamesD

P420 is the code for the rear O2 sensor. P400 series codes on all OBD2 vehicles mean emissions related. The rear O2 sensor will not effect driveability. The rear O2 sensor is just a monitor to see if the catalytic convertor is doing its job and how well. It does not control any fuel mixtures at all. It is just an emission device. Your front O2 sensors are the ones that effect the a/f ratio and can cause drivabilty problems.

James

SnoViking

132,000 miles.... but i have NO idea of previous history....

JamesD

I would recommend changing all of them for better gas mileage and driveabilty. If you dont want to change all of them but you want the check engine light to go out, then I would put in a rear O2 since you have high mileage I would start there. No guarantee that will turn the light off. If you are knowledgable you can do what you said but you have to have a decent multimeter that is fast enough to read the mV of the O2 sensor.

Also since you live in PA, doesn't the annual inspection have something for the check engine light being on? NY does and the car will not pass with it on. So basically if you state has this law and your inspection is do soon you may want to get it fixed.

James

SnoViking

yeah in PA if the check engine light is on.... you instantly fail the emissions inspection... and once you fix the problem a whole new inspection is completed... so you get nailed with 2 emission inspection fees plus the cost of the repair... luckily i dont go for inspection till june.... so i have alittle time to fix the problem... you said to "replace all of them"? this being? both O2 sensors and both cats? or what?

ok guys... im placing my trust in you guys and your experience.... im going to replace the rear O2 sensor.... im going to look online for the toyota part... so i hear the go only with a toyota OEM.... so theyre worth the money??? im hoping you guys dont let me down here... but i dont think you will... my faith is in yotatech


pat

JamesD

I used aftermarket many times and no problems. Advance Auto has lifetime on the O2's I think. Just to let you know they aren't cheap. Some dude here works for Toyota parts and says he can get them sweat shop cheap I dont remember the guys screen name.

James

SnoViking

are there 3 wires or 4 wires on the oxygen sensor? i thought there were only 3 .. but all the new oxygen sensors say they have 4 wires? and what brand is good? bosch, denso? it says the denso is the OEM? im so confused :cry:

JamesD

Denso is OEM. I would recommend that. All the O2's on your truck are 4 wire. They shouldn't ask you how many wires it has.

James

SnoViking

thanks james.... you rock