catalytic converter and oxygen sensor replacement?

interesting how the sensors on the Pathfinder are. I found 2 sensors right by the engine. so those would be the two sensor #1. the two sensor #2 were each before the CAT.

I bought a hayned manual and it even said that the sensors were before and after the CAT. I did not find any sensors after the CAT. lo and behold, the two other sensors were right by the engine.

You don't need an oscilloscope. A volt/ohm meter is all that you need. An old fashioned dial-type is very easy to read - just watch the swings of the needle, stick your left index finger at end of the needle's movement to the left, your right index finger at the end of the needle's movement to the right and you have your min/max reading. A Fluke with a max/min freeze also works, or if you're cheap like me, read the display on your $19 Radio Shack meter fast. I've been wanting a nice Fluke meter for a long time but have yet to come across a situation where my 20 year old cheapo Radio shack meter hasn't sufficed.

In fact, I have to break out the meter soon because our 4-tube, 2-ballast fluorescent kitchen light only works intermittently. I've changed all 4 tubes and both ballasts with no effect. A friend suggested that I actually measure at the neutral and switched leg so I guess that is my next step. The kitchen previously had 2 light fixtures, I'm covering the unused box with the fixture and feeding the fixture from the other box. Any hints from Gord?

Ray: Dealer indicated in disgnose receipt that "Diagnose catalytic oncverter internally worn", I am not sure what exactly it means? Since my car just passed state inspection 2 weeks ago done by the same dealer, do you think such "CAT internally worn" should fail the inspection at that time instead fails now? The other interesting thing is that currently the check light is off now after dealer's technician's diagnose, I am not sure how long it comes back. Thanks.

How to reset check light? I don't have tool to check the DTC. The code was checked/given by the dealer. I may need a tool, and what is it called for checking DTC?

Thanks

No. If the convertor is dead, then the stuff coming out of the convertor is no worse than the stuff going in. Your pre-convertor O2 sensor has already been exposed to that "stuff" (and always is). The 02 sensor after the convertor is not more fragile or easily damaed than the one before.

Regards,

Ed White

If the light is off, just keep driving until it comes back on. Do nothing! Don't panic!

Ed

Your car is compliant to On Board Diagnostics, Level 2 (OBD II), and you can do a search on the Web to learn more.

AutoZone (an auto parts store) will let you use the coed reader for free. The reader will reset the codes. There are readers on eBay that cost in the range of about $60 to about $150. There are four models from the same maker that have varying features and abilities, my suggestion is that the tool costing in the mid range is the one tha tmost of us ShadeTree mechanics will need. If you have an AutoZone store nearby, and don't want to buy another tool that won't get much use, then go to the corner and use theirs for free.

When you search the 'net for "OBD II" yo will find more than you ever wanted to know. Do the same search on eBay, and you'll uncover lots of sources for the tool. AutoZone has them for sale, or you can use theirs for free. If you want to use it in the parking lot, then you just leave your driver license as a security device. If you want to take the tool home, then they will ring it up on a credit card, then give a Full Refund when you bring the tool back. I've used the tool both ways, in the parking lot and at home.

Good point about the emissions warranty. The OP should check his Emissions Warranty since it will be different than the so called bumper to bumper warranty.

Checking the after converter O2 sensor is not as easy as the pre converter O2 sensor. For the pre-converter sensor you can just make sure it is switching voltage around 0.5 volts are something similar. In the case of the rear sensor, the voltage output should be almost steady when the converter is working. About the only thing you can do is check the output with the car (and converter dead cold) and then watch what happens as the car warms up.

Here is a description of the relationship for the two O2 sensors from a GM service guide (Toyota will be somewhat different depending on which type of O2 sensor is used):

"P0420

"Three-way catalytic converter (TWC) efficiency is measured by how well it can store oxygen. The ECM monitors converter efficiency by comparing the voltage values of the heated oxygen sensor 1 (HO2S-1) and heated oxygen sensor 2 (HO2S-2). Under normal operating conditions, the HO2S-1 should vary between 10 mV and 1065 mV and the HO2S-2 should remain relatively steady between 500 mV and 800 mV . This steady reading of the HO2S-2 indicates a correctly functioning catalytic converter. When all parameters have been met, the ECM will run a 5 second DTC P0420 diagnostic at idle. The ECM will command rich and monitor the time it takes the HO2S-2 to go rich. It will then command lean and monitor the time it takes the HO2S-2 to go lean. The longer it takes the HO2S-2 to change rich/lean means the converter is storing oxygen and is functioning properly. If the five second test fails, the ECM may take several tests during several ignition cycles to set the DTC. DTC P0420 sets when the ECM has determined that the catalytic converter is no longer efficient."

Ed

Jesus H. Christ! You have way more tools than I have! ;-)

I have several DVMs, one is even a Fluke. But none lock on the high or low reading. My Fluke is auto-ranging, but that won't help much here.

According to Bosch USA's web site, all OBD II vehicles are required to have an O2 sensor after the cat.

I don't understand the reason for a setup with an O2 sensor right by the engine and another before the cat because they're measuring the same thing - exhaust gas before being reated by the converter.

Some vehicles have converters attached to the exhaust manifolds under the hood and not under the vehicle, and they have a resonator that looks like a muffler or catalytic converter under the vehicle. It's possible that you were looking at a sensor in front of a resonator and not in front of the cat.

that's probably what it is then. I will check my hayens manual and see where exactly the CATs are.

what's the purpose of the resonator?

Your CAT is fine. Replace the sensor then see what happens next.

That's even better than replacing the sensor now.

Do nothing until the light comes on again, then pull the codes and go from there.

Remember, the CAT is a High Profit Item that dealers love to sell if they can.

I have more tools? I don't think so. I'd like more but I get by with what I have. Most of my tools fit in a 3' wide by 6' high tool box, other than drills, saws, long crowbars and pry bars. I try to get quality tools when I can justify them - I prefer Snap-On for automotive tools and Klein or Greenlee for electrical, Craftsman for tools that I use occasionally. I try not to do plumbing because I suck at it. A Harbor Freight store opened up fairly close to where I live, they are a good source for cheap tools that you'll use once and probably never use again.

You can go to most auto parts stores and borrow one for free. The scan tool is an OBD-2 scan tool. Just read the instructions with the tool.

In the U.S., the federal emissions warranty is 5 years, 50,000 miles.

Good point!

Basically, a resonator is a fancy name for a muffler - it changes the exhaust sound.

Autozone here in MI will do the reading for you. I never bothered to ask if I can use it.

Talk about Harbor Freight. I'll be buying some tools there soon once I do my own repairs!