I had a diagnostic code P0141 (bank 1 sensor 2 heater circuit). I verified the heater circuit was bad with an ohm meter (heater was open circuit). I could not get the sensor out of the catalytic converter and was worried I was going to break something so I took it to a shop. When they took it out the threads came out with it. They didn't do exhaust work so they drove it to an exhaust shop they work with. They were able to weld a new bung on for $75. Life was good until the next day driving to work my check engine light came on again. This time it is a P0420 (catalyst efficiency below threshold). Can I only assume they screwed up something welding the new bung on?

I called another shop today. The guy said he could put a universal cat on for about $250 including labor but in 60% of the cases it will still throw a code because the flow is different. A "direct factory equivalent" would run $700+ installed and he still wouldn't guarantee the check engine light wouldn't come on. Any thoughts on what I should do?

 

If you had a bad upstream o2 sensor then that could cause a lean or rich condition that would damage your cat converter over a long period of time. Welding shouldn't damage it since they're meant to take high temps. Up to 800˚F. But it could have been dropped.

However, it may not be the sensor. I would check your downstream sensor. There are a few things you can do:

• Knock on the cat converter with something hard (preferably after a drive). If you hear rattling then the honeycomb has broken. Its gone bad.

• If you have a scanner (or you can go to autozone or advance auto) and set it so that you can see both o2 sensor voltages. Rev the engine up to 2500 rpm and watch to see if the two sensors' voltages are roughly the same. If they are consistently the same then you most like have a bad cat. It means there's no change in oxygen before and after the cat converter. If just the downstream sensor is bad then you would see it behaving erratically.

• Another technique is to take an IR thermometer and rev the engine to 2500 (when its up to temp). Read the temps of the pipe just before and just after the cat converter. If its clogged then it will be significantly hotter before the cat converter. You can also verify a clogged converter by using a vacuum gauge on the intake. Rev the engine and hold it. If the needle slowly drops towards 0 in/hg then you have a clogged exhaust.

If you do need a new cat converter I would recommend eBay. Mechanic prices are insanely stupid. If your cat converter is a bolt on, buy the same one and replace it yourself. Then sell your old cat online. I sold mine for $115 and bought a high flow one for $120. Don't pay a mechanic a few hundred to do an hour's worth of work. They also gain the profit of the old cat converter.

Honda Accord 2003 2007 V4 2 4L Direct Fit Catalytic Converter | eBay

Magnaflow 27405 Direct Fit Bolt on High Flow Catalytic Converter 49 State | eBay

These are both bolt ons. I'm assuming your stock one is too. The first is OEM, the second is a magnaflow high flow. I have one and it works great. Just a slightly louder exhaust.

If you do need a new one then most likely you will need a new downstream sensor. I've found it good measure to replace the sensors if you ever need to replace the converter.

Heres a Denso downstream sensor if you need one.
Denso 234 4797 Oxygen Sensor | eBay

And finally, quick tip with getting things out is heating and cooling. I love my propane torch and breaker bar combo. I once had a stuck o2 sensor to remove from a car. Took me and another person pulling on the ratchet to get it out. I find the hex side of a wrench and a mallet work much like an impact gun too. Great for loosening stuck bolts as it tends not to strip them easily.

Hope that made sense. I kinda hop around the place and say a lot.

 

RockAuto too: 49-state Walker for $135 + shipping. X2 for selling the old one online for $75+. An exhaust shop probably wouldn't charge more than $50 to swap it out if you brought your own parts.

 

Thanks for the Ebay link. That's quite a price on the direct fit! The downstream sensor is what started it all. Heater element was bad and no other codes. What's in there now is new, they just had to weld a new bung on and after that I had the P0420. I have the "Torque" app for my smartphone and cleared the P0420 code. One day of driving and so far so good. With Torque, it seems I can only watch the voltage of the downstream O2 sensor, not the upstream one unless I'm missing something. It would be nice to overlay them. Thanks!

 

Ok. I was under the impression that you had your upstream sensor changed.

Sometimes I've seen the repair process is to change the downstream after seeing an 0420 and then if that doesn't work then change the cat converter. Keep in mind that if your downstream went bad and then your cat converter went bad then there may be an underlying issue. But thats not definite right now.

If its a narrowband sensor then on torque you want "o2 volts bank 1 sensor 1". But you may have a wideband sensor. thats under "O2 Sensor1 wide-range Voltage".

You will see the sensor in green taking readings and in blue when selecting them with the engine running. That will tell you which one should work.

Unfortunately you can't really compare wideband sensors with the downstream just like you can with narrowband. But if you choose the graph setting for both you can compare them.

On torque you can see the widget "Emission monitors since DTC clear". Take a look at "catalyst" and see if its complete or incomplete. Thats your cat converter. If its incomplete then you may have a CEL coming (or the ECU hasn't checked yet). For my car at least, the ECU checks the cat converter after driving on the highway for 20 minutes at 55mph and then coming to a stop.

 

Sorry for the delay in posting. On Torque, the only thing available on O2 Sensor 1 is the "Equivalence Ratio(alternate)". "No data received" is whats reported on anything else to do with the upstream sensor which I guess is technically called an AF sensor? On the Emission Monitors page, it reports catalyst and evaporative system tests as incomplete. I have driven a few hundred miles since clearing the fault (40 miles round trip to and from work mostly interstate driving). With the car at operating temperature and cruise control set at 75mph on interstate, the downstream voltage is pretty consistent at .6V. When accelerating or decelerating the voltage varies quite a bit.

Even though there is no CEL, I ran a code scan and it came up with nothing. Is it supposed to report "pending codes"? I really don't even know the criteria for a pending code. Thanks.

 

I once gota cat Red Hot for a different reason--it died two weeks later

 

A pending code shows up on Torque if the ECU flags an issue during the first readiness code scan. The ECU has to go through the list two times in order to display a CEL.

AF sensor is any o2 sensor- upstream more specifically I believe.

Choose the widget called "Fuel Status". It is in the middle if you scroll down on the first menu. That will tell you if the car is in open or closed loop. After a few minutes of driving if it's in closed loop then its using the o2 sensor.

On torque there are several options for o2 sensors. I recently checked a Golf and the upstream was sensor 2 and downstream was sensor 3. For my car it's 1 and 2 respectively.

With the program connected to the running car, start at the first o2 sensor option and scroll down. Look for those options that are highlighted in green.

You may not have seen the "O2 Volts Bank 1 Sensor 1", starting from there down is your best bet to find what monitor it's picking the sensor up from. If you have a narrowband o2 sensor and not a wideband one.


However, if your readiness codes have all gone through except the cat converter and evap then your o2 sensors are most likely fine. You may get a p0420 then. If thats the case, follow the procedure for diagnosing a bad cat converter or go ahead and replace it anyways.

Sold my old cat converter to these guys. As easy as throwing a prepaid ups label on the box and sending it in. A week later I get $115 in my paypal. Just about paid for the magnaflow.
http://www.sellyourcatsdirect.com/

 

I found the "Fuel Status" widget and reports closed loop after just a few seconds after starting the vehicle. "O2 Volts Bank 1 Sensor 1" is always reported as "no data received". I looked through the dozens of O2 sensor options and like I said the only one that was showing a status was "O2 sensor 1 Equivalence ratio (alternate)". This value is nearly always .99 which seems nonsensical. I guess all I can do is play the waiting game and see if the Emissions Readiness ever finishes or if it eventually throws a CEL. Here is a screen shot from my downstream O2 sensor and other info going down the highway:

 

Now I see. You have a wideband sensor from the looks of it. I see the AFR widget is reading. Did you see anything under the wide range voltage sensor options?

Although it does look like everything is doing ok right now.