Bank1 Sensor1 Voltage 2004 V6

Can anyone tell me if my Bank1 Sensor1 voltage is correct, I have a 2004 Tacoma v6 and have gotten the dreaded p0420 engine code and have replaced the 02 sensors(both) with Denso,cleaned the MAF,replaced the PCV but the p0420 comes back on so I am figuring on new Cataylic converters are due the engine has 245K miles. But I have been monitoring my o2 sensor voltages with a OBI code reader and am getting 3.25 volts(steady no fluctuations)Bank1 Sensor1 the A/F and anything from .095-.800 volts all over the map for the rear Sensor2 which tells me bad cats? My question is my Sensor1 voltage at 3.25 volts correct? From what I am reading the Sensor1 A/F should be fluctuating where mine stays at 3.25 volts with no fluctuation. Also I found http://www.markofshame.com/fsm/01_Tacoma/Seperates/Service manual/211.pdf this searching can anyone tell me if my Sensor1 is in the true specs voltage for my ride?

 

I am trying to determine the same thing with mine. I read an article here:
http://forum.ih8mud.com/threads/narrow-band-vs-wide-band-oxygen-sensor-summary.168494/

Have a better understanding what I'm seeing now. It would SEEM that range is ideal for the front sensor. 'No' changes/fluctuations indicates its frozen up. But it should fluctuate a little. You can also test by creating a vacuum leak and watching the sensors just the same. I pulled of the big plug on the front of the intake and it jumped past 4. But yeah mines "steady" at idle around 3.28 but does fluctuate a tiny bit. The rear is the narrow band and should be that low. Mine stays fairly steady but jumps around a lot more than the front. Around .4/.5... But does jump up and down steadily too. The code you got was basically saying that your cat isn't up to par. It could be clogged. Or it could barely be out of spec. From what I understand anyways.. I've recently got a whole new exhaust system installed. Got a lean cel once. Had my o2 SIM before the new exhaust which I unplugged after new exhaust and took a long time and finally popped the cel for that too again. Cleared and hasn't came back on. Everything on mine SEEMS to be working properly. But still experiencing high fuel trims, and sluggishness. I'm going to be replacing the maf and see what that does first. Then front o2 sensor. I might even suspect the fuel pressure regulator. I really have no clue. So I'm just gonna start with the cheapest and work my way up. I'm crossing my fingers and hoping it's the maf. Or at most the front o2. As far as the rear o2 and cel you got, there's a few things it COULD be besides the cat. I would test the cat efficiency first. Either with a vacuum gauge, or with a back pressure gauge. Or even a laser thermometer is supposed to shed a clue. Look on YouTube for vids on the thermometer method. I couldn't really decipher if they were clogged from just that but it may provide a clue and easiest to start with. Otherwise it could be your sensor(s). Idk. But I'll report back after I've done some more testing. Be a while though. Good luck till then. Maybe someone else will chime in with more info.

 

Oh I didn't even see the link you posted. That helps! Well you should be able to test it with that! But it looks to be normal. But need to test and see. Hopefully it's not my ecm.. don't even know what that does. Ha. I'm gonna see if I can test the fuel pressure regulator first. And run through that diagnostic you posted! I'll let you know when I get to it. Next week on Monday probly.

 

Thanx for the reply seems as if we are having the same problem?(if it is a problem?). Im having trouble understanding that link I posted if that having a 3.30 volt reading is ok for the sensor1? Mines almost steady 3.25volt(new Denso sensor) with slight fluctuation, my scare is to buy install all new Cats and exhaust only to find out the truck is running Rich(fuel) and causing the CEL and screwing up the new cats. Most threads and YOUTUBE vids are saying that the Sensor1 should fluctuate from 0.095-.500 volts? mine is stuck at 3.25? WTF I wish someone who might know about this would chime in.

 

The A/F Sensor is designed so that at the stoichiometric set point of 14.7:1 there is absolutely no current flow and the resulting voltage signal put out by the circuit is 3.3 volts.

A rich mixture which leaves very little oxygen in the exhaust stream, produces a negative current flow and the circuit will produce a voltage signal below 3.3 volts.

A lean mixture which has more oxygen in the exhaust stream, produces a positive current flow and the circuit will produce a voltage signal above 3.3 volts. < Quoted from your article

 

Yes that voltage reading is normal for the front sensor. It's the wide range voltage. So it seems that our sensors are working at the proper range. And if your rear sensor is working as well, then I would suspect the cats. Again I would test the cats. For back pressure. You could also test them for serious clogging with a vacuum gauge. If you hook up to a vacuum line with gauge and rev at (iirc) 2500 rpm steady, the vacuum should stay steady in the 'good' range. Can't remember what the number should be. If it gradually drops, then it suggests your cats are probly clogged.. When mine did this, I suspected the cats but never got around to testing them properly. I assumed for sure it was them and was planning on doing new exhaust system anyways in the future. So in the meantime I had bought the urd o2 simulator for the rear sensor. Which you could do as well. But it's really only meant to get rid of the cel. Not fix any problems. Kind of a waste of money now thatI think of it.. But now that I got my new system installed (magnaflow high flow cat/resonator/borla muffler) from y pipe back, I didn't notice a huge increase. None at first but now I can feel she's opened up a bit more. First code I got after a day was p0170/p0171( can't remember) too lean, but cleared and it hasn't came back.I had unplugged the simulator as well and it took quite a while for it to pop the p0420 code again. Cleared and it hasn't came back on either, yet. If it does I'm putting the SIM back in. It might pop the cel just because of the higher flow now regardless.

So... I would test your cats first.
Are you experiencing any performance issues?
Decreased mileage?
Sluggishness at highway speeds?
Hard starts?
Rough idle?
Done regular tuneups?

Anything like that? I'm starting to lean towards a fuel problem myself. I was gonna test the fuel pressure (fuel pump) but don't have the right fittings. I believe I can test the pressure regulator. I think that's vacuum. I might even suspect injectors. Again I'm gonna be trying a few things. I gotta take my whole intake off too pretty soon for an internal coolant leak so I'll be looking into getting the injectors cleaned while I'm at it.

But the p0420 could be a number of things. If you don't already know or looked it up yet, check this link for causes/symptoms/ and ways to diagnose.
http://www.obd-codes.com/p0420

 

no I have none

So... I would test your cats first.
Are you experiencing any performance issues?
Decreased mileage?
Sluggishness at highway speeds?
Hard starts?
Rough idle?
Done regular tuneups?
I would hate to invest in cats or aftermarket parts only to have the code light come back on(waste of time and money?) Maybe best to get OEM cats and aftermarket catback exhaust(Gibson). I feel confident that the 3.30volts is normal for sensor1,my last check mines 3.285volts close enough. I changed out my fuel pump at 244,837miles was still going good,but I fixed a leak at the top of my tank figured might as well change the pump while im in there,runs a lot smoother now.

 

Again, you need to test your cats. Get a back pressure tester. Only way to tel for sure. They could simply be BARELY out of spec throwing a code, and still be flowing properly. Then you could get the simulator and not replace anything. Unless of course it doesn't pass emissions if you require that, which I don't..

 

jep we have Cali emissions here so I get the sniffer in the pipe,so simulator not going to work

 

I would still test them. And maybe run through emissions and see. 2nd emissions test should be free right? At least it was when I used to go.. before you dump a bunch of money into new cats. I don't really know anything about how strict cali is. Maybe you'll get lucky. Clear the code run through and pass. Idk.. Could even be the rear sensor but it seems to be working. Have you replaced that one or just the front?

 

Both Sensors 1&2 have been replaced(DENSO).
I am thinking the same,if it does go through then I get another 2 years till next time,I got a new OBD reader that monitors real time so if I can sneak it thru then im good. But I noticed there is a IM function on the Reader that tells you when all the systems on the truck have been checked and ready and gives a Green light to tell you alls been checked by the system and alls good(green light),but as soon as the Cat portion of the testing is confirmed and ready>that's when I get the check engine light P0420. Also I want to throw out there as far as the Sensor1 A/F voltage goes is that voltage supposed tp be a SOLID 3.30 volts? or is a slight fluctuation OK? Mine has a slight fluctuation at idle full operating Temp. on the low end say 3.265v-3.29v and sometimes hits 3.30v-3.31v. I wish a Toyota tech or someone can really verify that its OK,cause that might be my issue flashing the P0420(maybe) cause its might be running rich and throwing the Check light? Wheres Bama Toy when you need him

 

Is there any chance you got the answer to this question? I recently got the manuals and have similar issue. Will be posting my solutions and findings as they come.