fish0281

I've had the P0420 CEL going for a bit now, along with a distinct loss in fuel mileage (21 MPG --> 17.5 MPG), so I decided to buy a bluetooth OBD II dongle and use the Torque app for my Android.

It is a sweet app btw - I'm able to gather a lot of real time data, but the one sensor I was primarily concerned with, the AF/upstream O2 sensor (sensor 1) is not detected by the scan tool! What gives? I can see sensor 2, fuel trim levels, af ratios, open/closed loop, etc... but no sensor 2 voltages.

I have about 170k miles on my 2001 SR5 and not sure the last time the sensor has been replaced, so I have another one ready to install. The nuts are rusted and mangled (not really sure how/why), so I'm pretty excited to get to it. pfffft.


Any way, does any one know of a logical reason why this sensor isn't showing up in the scan?

mt_goat

P0420 is generally the failing cat code. (Cat below threshold)

fish0281

I'm aware of what the P0420 code means, but the end goal of this post and my intentions that led up to it, are to ensure that my sensors are functioning properly. It's entirely possible that they may be the cause of the code flashing, and it'd be a real shame to spend as much [$] as is required to get new cats when it's actually a bad sensor...

mt_goat

Yeah I wouldn't buy new cats. A simulator fixed my 420 problems.

TheDurk

If you have an A/F sensor, a voltage scan is not going to tell you much of anything anyway. The wideband A/F sensors work completely differently than the standard o2 sensors--the voltage is set by the ECU, and what varies is the current and that is measured by the ECU and used to control trim. My BR-3 hookup just shows a flat line for the A/F voltage. This may be why Torque doesn't report it.

The mangled nuts are totally normal anywhere in the salt belt and are a pretty good sign you are due for a new sensor. However, P0420 is usually thrown by a degraded rear sensor, if it is not an exhaust leak or the cat is indeed bad. Change the rear first. I cured my P0420 that way. The rear has NO effect on mpg, the front one affects that.

I just got an Android tablet and an ELM 327 dongle for newer cars than my ancient BR-3 can handle, but I haven't tried Torque on the 4Runner yet.

fish0281

Yeah, I am not interested in solving my problems with a simulator - they're great for some situations, but not me. The engineer in me would never be satisfied until I actually know what's wrong... if I were yanking the cats, that'd be a different story.

That's good to know the AF sensor operates differently and probably a good reason it doesn't show up at all on Torque... I'm still suspecting it's the front sensor because (1) the drop in fuel mileage (the sensor is forcing a rich condition) and (2) the rear output is a steady voltage of about 0.7 at idle. IF the AF sensor is in fact forcing a rich condition, could that be the "cause" for a P0420?

Either way, they'll probably both get replaced since I suspect if one's bad, the other will go shortly there after. Odd thing about the nuts on the sensor is that they're not *too rusty (the truck lived in OR originally, no salt), but it looks like someone put them on with a vice grips. There is literally chunks of metal sticking out preventing me from getting a wrench on there... vice grips and torch, here we go!

mt_goat

Yes, the FSM lists sensor 1 as a possible cause of a P0420:

More from the FSM here:http://www.ncttora.com/fsm/2003/Repa...fe/cip0420.pdf

Since you have the scanner, is your ECU running in open loop a lot or all the time with the 420 code on? If not, what are your fuel trims showing?

fish0281

As soon as the engine is warm, it goes into closed loop and stays there. Both the long and short term fuel trims are below 5%...

Oddly enough, the light shut itself off on Friday and I've since put about 100 highway miles on without it coming back (in the Mountains too). However, I'm still getting about 16.5 mpg, where as right before the check engine light happened, I was getting 21 mpg (highway of course).

fish0281

Ok, a bit of an update...

1) I clocked about 18.5 miles per gallon for the last 100 miles (driving between Denver and Boulder for work)

2) The check engine has stayed off for over 200 miles with multiple restarts.

3) PB Blaster is simply amazing. Somehow I've never used the stuff before, but I will not be without a can as long as I'm working on my own vehicle(s)

4) I swapped out the AF sensor for a new one - Denso 234-9002 - and it took me all of 10 minutes :-D I'll report back on my fuel mileage after this tank (currently full)

5) I noticed that my front and rear cats are separated by a flange - did it come this way from the factory? For some reason I had it in my head that the factory built it as one contiguous piece (no flange between the cats)...

fish0281

Another update:

While driving up in the mountains this weekend, I gave 'er hell around a snowy corner, traction control kicked in, and so did the CEL... P0420 again. So, the new A/F sensor didn't do it and I'm still getting terrible gas mileage. On my way back to Denver, while sitting in the infamous i-70 traffic, I noticed a very distinct sulfury-eggy-stink; hard to tell if it was coming from my truck though.

My scanner shows reasonable output from my O2 sensor (constant 0.7 volts), so I think my next step should be to replace the cat(s)...

Anyone know if replacing the front cat only could fix the problem or is it likely that it'd be both? Also, anyone know the difference between the front/rear catalysts (i.e., which catalyzes what)?

SnoViking

bump... Im in need of similar info...

fish0281

I came across some additional information yesterday/today when I noticed my truck tends to idle pretty low, which could be related to the throttle body, or the O2 sensor (or maybe something else...). Also, the light shut itself off again.

So, I'll be putting in the O2 sensor tomorrow or Thursday. My theory is that the sensor is getting sluggish and doesn't respond as quick as the AF sensor, thereby popping a (P0420) code.

I'm planning to take the throttle body off tonight and give it a proper cleaning, including the IAC, to see if that cleans up the low idle and *maybe the fuel mileage issue...

Lastly, I honestly don't remember if I've replaced the plugs since I bought this thing (<30k miles ago), but does this plug look like it needs replacing?

TheDurk

Cats are two different pieces joined by a flange. I just got my first P0420 since I replaced my rear sensor two years ago so I am now using my Torque for the first time. Mt_Goat posted correct FSM for P0420, but test routine for A/F sensor is here (p. DI-55): http://www.ncttora.com/fsm/1996/SIL/...e/cip0171p.pdf

Hope this helps.

fish0281

I cleaned the throttle body and it was pretty dirty. However, it wasn't until I had the TB off the truck until I realized that 2001 and 2002 4Runners have the IAC integrated into the TB... i.e., it is not possible to clean/replace the IAC w/o replacing the TB.

All that being said, the idle was periodically as low as 600 rpm (once it is fully warm and well-driven it would be more like 700 rpm); after cleaning it went directly to 700 once warm.

I also noticed the O2 sensor voltage bouncing around a bit more today - the values ranged from about 0.2 to about 0.8 volts. My CEL is still off and I haven't been able to estimate my mpg yet; but we'll see what affect a new O2 sensor does (tomorrow hopefully)!

fish0281

Last night I found a plug wire out of spec (resistance was greater than 25k ohms), so I put in a new set of NGK wires. Also replaced the O2 sensor and put in a new PCV valve since the old one had quite a bit of gunk in it...

I also did some diagnostics on the throttle body sensors, thanks to the super sweet FSM link that's floating around the interwebs; it looks like everything is up to snuff on the TB.
Summary of what I've done in an attempt to solve my P0420 and low idle issues: new AF sensor, new O2 sensor, TB cleaning, new plug wires, and new PCV valve

So far, it seems a bit more snappy and the idle rpm's are right where they should be.
Hopefully the problem is solved and I can get back to my +20mpg highway rates! My weekend trip to Summit Co. ought to be a good test...

fish0281

About 1k miles later, the P0420 light popped back on today. Still getting lower than usual mileage. I think the only thing left to do is replace the cat(s). For the record, I'm not interested in using an O2 simulator.

Does anyone have any experience with the Magnaflow cats (49505 and 49579)?

Would it make any sense to try replacing the front one first to see if that clears it up?

The best price I've found is on Amazon @ $290 and $330 respectively...

fish0281

Does anyone have experience with Bosal or Eastern converters? There are some cheap prices out there for Eastern, but I don't want to throw money at something that'll just $h** the bed in a year. On the other hand, I have a family-connection to a shop here that said they can do diagnosis and replace them (if needed) with Bosal for about $650...

Is there an advantage to using Bosal converters (for more $$) over Eastern converters? or is anything less than OEM a roll of the dice all the same?


Also, has anyone know if an ECU flash is required after replacing the cats? I assume clearing the code would be enough, but the shop owner mentioned it was a necessary step.

FogRunner

Fish you made mention the "engineer side of you", well as any engineer you will understand that battle between good engineering vs. cost which is the situation your in. You MUST either go with OEM (over $1000 cats) OR use a aftermarket can WITH a 02 sensor simulator.

The reason being is the 01-02 4runners are ALL California emissions and the computer is calibrated to see a VERY high efficiency catalytic converter (OEM Calif spec converter).

But if you use a Borsal/eastern or any other non-California spec catalytic converter the efficiency of it brand new freshly installed will still be well below the threshold of what is the acceptable lower efficiency of a California spec converter.

To fix this issue your going to need to run a O2 sensor simulator and for more than just keeping the P0420 code away.

Most vehicles use the rear O2 sensor to monitor catalytic converter efficiency and that's it but Toyota has it do more but I will get to that in a second.

So with a normal running engine the computer is constantly making the engine rich then lean several times per second so as to have oxygen rich then oxygen void exhaust for the oxidation and reduction sections of the converter to function.

If you put a O2 sensor just before the cat you would see a almost perfect sine wave of the engine going rich (low voltage low O2) then lean (high voltage high 02).

Now if you monitor the O2 sensor behind the cat converter (that's working properly) you will see pretty much a voltage that is the average of the sin wave we saw pre-cat converter.

BUT if your cat is totally gone it will give you the same sin wave signal on the rear O2 sensor as seen on a scan tool as the voltage going very low then very high.

So on most vehicles you can just cut out the O2 sensor, throw on a simulator and the computer will be happy but as said above Toyota uses that rear sensor for more than just cat convert monitoring.

What Toyota does that is special is to deal with the aging of the front Air/Fuel sensor the computer will periodically run the more lean for several seconds then more rich for several seconds and look at the change in the average signal from the back sensor to re-calibrate the front sensor.

However if you have a BAD cat converter the rear sensor will be producing a sine wave signal rather than a steady voltage that will slighlty increase and decrease with the calibration lean/rich attempts of the computer.

So what will happen is the computer will see its unable to calibrate the A/F sensor and go to a fail safe that runs the engine rich which kills the mileage.

So despite what people say the rear sensor can and does affect gas mileage. Here is a link to Toyota's patent on the very system. http://www.google.com/patents?id=e1Q...54&output=text

Now on the issue of a O2 sensor simulator. There are really two types of "O2 simulators" but only one is really a simulator and you want to avoid that. The true simulators remove that rear sensor and do nothing but take the voltage in from the computer and give a average voltage back that the computer would expect from a good working cat converter.

The proper kind of "O2 simulator" isn't a simulator at all but actually a signal conditioner. What it does it sit inline with the O2 sensor and take the sine wave that the sensor is producing and "averages" to give a constant voltage that the computer expects to see for a properly functioning cat.

But with using a signal conditioning type of sensor simulator, the computer is able to re-calibrate the Air/Fuel sensor as it normally does. When it increases the amount of time the engine is lean or rich it changes duty cycle of the sine wave and then the sensor simulator "averages" the sin wave in the same way cat converter would.

And no there is no "flash" required after replacing the cats or replacing them and adding a simulator. But you need to disconnect the battery for a couple of minutes. This will clear all codes but most importantly the computer will want to check the condition of the air/fuel sensor and will attempt to re-calibrate it against the rear sensor once the engine is hot and running at constant speed IE highway driving for about 20-30 miles.


FOG

fish0281

Thanks for the great input Fog. I understand the signal conditioner and the cost vs. quality points you brought up, but a few things still don't quite make sense to me...


I know that the '01 model year (and other years) runners all came equipped with the same emissions control components, but does the ecu and/or O2 sensor operate with the same threshold of CARB standards regardless of the vehicle tag?

For example, my truck has a EPA tag and as I understand it, the EPA requirements are less stringent than CARB... so is the EPA tag just a label that serves no functional purpose to identify this truck separate from the CA ones (as it pertains to the emissions controls)?

That being said, wouldn't that also mean that when cc manufacturers advertise their products as "EPA compliant" it is basically a misnomer (as it applies to these 4Runners anyway)?

What about CARB approved aftermarket cats? If I remember correctly, Catco and Walker have some on that CARB list of approved mfg's...
Does the URD simulator properly condition the signal?

If the truck were a bit younger, I would probably just go the OEM route, but it's not and the 170k miles it has seen is probably what killed the cat... no pun intended. I could buy about 5 sets of Eastern cats for the price of OEM though.

fish0281

Here's an aftermarket CARB compliant cc (Magnaflow is the only one I could find): http://www.summitracing.com/parts/MPE-45006/


Its universal, so obviously it'd have to be welded in, but it is a fraction of the OEM price... same story as any aftermarket cat though?