2001 Toyota 4Runner (P0770 and P0420

you have a catalytic converter efficency code and I think the code the po770 code is tranmission related! Get it checked by a better mechanic! The emissions code po420 is cause for failure for the emissions test and the tranny code if ignored could lead to more problems then just a failled test! Ignoring lights is never good practice because at some point they have to be fixed and leaving it till the last minute leaves no budgetting, or time to properly diag it

I picked up the 4Runner tonight (From Toyota Dealership) and mechanic told be to drive around some more to see if the incomplete monitors fill in the information required in order to complete the emission inspection then mechanical inspection. I already drove 750 miles since the original reset. How long do I have to go till it becomes complete? The incomplete monitor that I'm talking about is the one for Catalytic (something). I wonder if this relates to the P0420 code that was originally there before the reset. Again anyone please advise.... Thanks[/code]

yes it does, if it doesn't go to complete then you have a problem with the converter, the 02's or an exhaust leak near the 02's

Check the troubleshooting procedures for code P0420. It could be a bad Cat. coverter, bad O2 sensors, a bad coolant temp. sensor, or bad exhaust pipes/components. What the code is saying is that the O2 sensors before and after the Cat. are sensing an inefficient Cat. This could be from several things, like the ones stated above. On my 2001 Nissan Altima, I have two O2 sensors. You might have more. The first one is in the exhaust manifold, and the other about 6 ft. downstream in the exhaust pipe. The Cat. is bolted right to the exhaust manifold. So it is between the O2 sensors. With 197000 mi. on the truck, I wouldn't be surprised if the Cat. has seen better days and some of the posts attest to that, but I would check out everything else before buying that. The first O2 sensor, when it's hot, will be reading a certain amount of millavolts. Mine is supposed to read between 100mv-900mv. The second O2 sensor I'm told is supposed to read a constant 200mv. You will need to have the truck up to operating temp. and possibly running to check these by back probing the connectors. Be careful and chock the wheels if you do this. Both of my O2 sensors are heated which I'm sure yours are too. There is a heating element in it. My back sensor has 4 wires on it, two for the heater and two for the sensing. If the heater element is out of range for resistance, then the O2 sensor will not work properly and set the P0420 code. My front O2 sensor has only 3 wires and a little different design but still has a heater. You should get the resistance values for your truck, they might be different than mine. The front and back O2 sensors do different jobs (although they are still measuring O2) and are physically different. The coolant temp. sensor is telling the ECM (electronic control module) what the temp of the coolant is (makes sense) and then the ECM is adjusting the fuel injector pulse as needed. Basically if the coolant is cold, then it gives the engine more fuel. If it's up to temp, then less fuel. If the sensor is bad, then you could be getting too much fuel all the time and that will screw up the Cat. and set the P0420 code. It will also ruin the Cat. if it runs that way for too long. Exhaust leaks change the exhaust air mixture, so to speak. Just like an intake leak changes the fuel mixture. Check out the exhaust system for any leaks, etc.

mackin212 wrote: Check the troubleshooting procedures for code P0420. It could be a bad Cat. coverter, bad O2 sensors, a bad coolant temp. sensor, or bad exhaust pipes/components. What the code is saying is that the O2 sensors before and after the Cat. are sensing an inefficient Cat. This could be from several things, like the ones stated above. On my 2001 Nissan Altima, I have two O2 sensors. You might have more. The first one is in the exhaust manifold, and the other about 6 ft. downstream in the exhaust pipe. The Cat. is bolted right to the exhaust manifold. So it is between the O2 sensors. With 197000 mi. on the truck, I wouldn't be surprised if the Cat. has seen better days and some of the posts attest to that, but I would check out everything else before buying that. The first O2 sensor, when it's hot, will be reading a certain amount of millavolts. Mine is supposed to read between 100mv-900mv. The second O2 sensor I'm told is supposed to read a constant 200mv. You will need to have the truck up to operating temp. and possibly running to check these by back probing the connectors. Be careful and chock the wheels if you do this. Both of my O2 sensors are heated which I'm sure yours are too. There is a heating element in it. My back sensor has 4 wires on it, two for the heater and two for the sensing. If the heater element is out of range for resistance, then the O2 sensor will not work properly and set the P0420 code. My front O2 sensor has only 3 wires and a little different design but still has a heater. You should get the resistance values for your truck, they might be different than mine. The front and back O2 sensors do different jobs (although they are still measuring O2) and are physically different. The coolant temp. sensor is telling the ECM (electronic control module) what the temp of the coolant is (makes sense) and then the ECM is adjusting the fuel injector pulse as needed. Basically if the coolant is cold, then it gives the engine more fuel. If it's up to temp, then less fuel. If the sensor is bad, then you could be getting too much fuel all the time and that will screw up the Cat. and set the P0420 code. It will also ruin the Cat. if it runs that way for too long. Exhaust leaks change the exhaust air mixture, so to speak. Just like an intake leak changes the fuel mixture. Check out the exhaust system for any leaks, etc. I'm in the same boat with the P0420 code. Right now I'm torn about what step to take next. Option #1 Buy a cheap OBDII reader ($50 range, as I don't have one at all), replace the after CAT 02 sensor and see if that helps. If that doesn't help replace the Air/Fuel sensor before the CAT and see if that helps. If neither work, then I'd take it in to get OEM CATS Option #2 (and really my question) Buy a nice OBDII reader ( http://www.canobd2.com/tool/3130.asp <---can get for $160 shipped or http://www.auterraweb.com/dyforwiusb.html <----about $190 shipped), both of which offer "Oxygen sensor monitoring and on-board test results" in hopes of determining if the 02 sensor/Air-Fuel sensor is the problem, instead of just replacing them (they cost about $300 combined). If they are bad, I would obviously replace them. If they show good, then I would have spent the money on a nicer OBD reader, but saved money I didn't need to spend on the sensors. I would then head straight to attacking the CAT problem. Suggestions on choosing option 1, 2 or other? Can those OBDII readers reliably report a bad 02 sensor (and do they scan the A/F sensor, or is it different than the 02 sensor)? I am wanting to attack this problem in the smartest way....and if I can get a tool that I'll get to keep for a long time and prevent replacing parts unecessarily, I'd love to do that. Apprciate the help!!

you're in the same boat with the same type of vehicle?

Sorry, I was a bit vague. I might not be in the same boat as ewiciak, but our boats are at least right next too each other I have the same vehicle (2001 Toyota 4Runner-V6 3.4L 4WD). I am pulling the same code=P0420, but not the P0770 (I have no transmission problems). My check engine light has been on for about a week (in that time I've driven about 500 miles). I am not needing a smog, I just want my car to be functioning properly and to ditch the check engine light. I have about 140,000 miles on my car and it has never had the 02 sensor, A/F sensor, or CATs replaced (that I know of, I'm the second owner). So my option #1 & #2 and the subsequent questions are based on that information.....sorry for being overly vague the first time.

The whole thing with catalyst failure codes is that you can replace the conveter and maybe delete the code that way but it's important to know what caused the converter to fail. Prolonged misfires, lazy 02's , burning oil or coolant, exhaust leaks near the conveter etc! So yes replacing the conveter is likely to fix that code but if the truck is in sad state of tune or has some of the other issues that I listted then how long the conveter lasts is questionable. Poor quality gas can burn conveters out as well!

My truck runs good. I bought it about 30,000 miles ago. Timing belt/water pump replaced (preventative), but other than that it hasn't needed anything or given me any problems I suppose I could do a tune up to be safe, but like I said the the rig runs good. Every few oil changes they mark that it is a half quart low (so most of the time they check "full"), I don't know if that would constitute it burning oil or not. As far as coolant goes, I don't think I'm burning it, but I'll keep an eye on it. As for the gas issue, I put in whatever I'm close to, and 87 octane. Is there a chance my CATs are just old?? This lengthy article: http://www.aa1car.com/library/p0420_dtc.htm about the P0420 code indicates (at the bottom) that the life expectancy of a CAT is about 150,000 miles. I'm a little under that, but not by too much. I really do want to get to the base of the problem, not just cover it up with new CATs (unless they are simply "worn out"). I am either going to just buy and replace the o2 sensors as a starting point or buy a nice OBDII machine in hopes of ruling out the o2 sensors. From what I've gathered here on this forum and here: http://www.4x4wire.com/toyota/4Runner/tech/OBDII_ECU/ it appears that the OBDII machine reads the signal of the o2 sensor and relays the information in volts: http://www.4x4wire.com/toyota/4Runner/t ... utput1.jpg This can then be checked to see if it's in the proper parameters. Is that correct? Is that a reliable way of determining if the o2 and AF sensor are working? Would you suggest a different starting point?

As far as preventative I'd start with a complete tune-up using the proper plugs and good quality ignition components, replace all the 02's as well becuase it may repair the po420 dtcs and if not you're mileage should improve if nothing else. Then should you still remain with the po42o dtc then replace the converter(s)

I still am amazed at how people who "replaced something or another" on their car one time, post innacurate data for a poster when they're dead wrong. FOR THE LAST TIME: A catalyst inefficiency code sets when: The PCM sees that the post cat. o2 sensor is switching at the same, or close to the same frequency as the front sensor. This tells the PCM that the cat. isn't working properly and it'smaking our air dirtier. So it sets a code. An O2 sensor that has failed NEVER, I repeat, NEVER switches too fast. They always switch slower or not at all. So, a cat. efficiency code popping up is never caused by a failed post cat. o2 sensor. OKay? Good grief!

Okay!

......uhh.....okay.

That's too bad....I just bought the new o2 sensor and A/F sensor To throw a wrench in things, my check engine light has gone off and stayed off for the last 150 miles or so. I have done nothing yet (no tune up, replaced nothing, etc.) Would this lead to the belief that it was possibly a bad tank of gas? Should I wait it out and see if it comes back on?

sure why not !