So I now know why the '01 I bought last week for $1200 was priced this way. The CEL came on with a PO 0420. I suspect the O2 sensor and will further test to make sure but have a question about the HCAC. Has anyone tried rebuilding the exhaust system without the HCAC? The Gen 2's have a very similar system, I believe, but without the HCAC. Given my minimal investment in what is a very intact '01, I am game to try putting a replacement system together. I would prefer to not spoof the system and there is no way I will buy an exhaust that costs as much as the car, although I might if I have to. It seems like a noble thing to try, given the cost of the stock system. And could be some frustrating fun. I know there are much more experienced people than me with a long record of working on the technical end of things. If I can ask for some guidance, please indulge me. There is no emissions testing here in Maine, so that is a first step. I would like to try to keep the system operating properly without the HCAC if at all possible. Plenty of time to sort these issues out. Will have it on a lift to check the valve performance. It seems to be moving okay. The CEL is coming on after operating at temp for about 20 minutes. Tom in Maine
I would first replace both 02 sensors and see what happens. How many miles are on the car? I really doubt that it is a bad convertor. Sorry I have no experience with trying to use an aftermarket exhaust..Let us know what happens.. By the way,WELCOME TO THE FORUM!!!
I am pretty sure the HCAC is not in that loop. Let me suggest: photos of the part and area - some have reported using high temperature lubricants and working the valve loose (WD-40, e.t.c.) careful on first start to have an extinguisher handy and able to work the area. Technical Information Service - download the sections dealing with HCAC and/or get the maintenance manuals (Ebay). Bob Wilson
High, I own a 2002 prius with a reinvolt battery and 207000 miles. My HCAC was squeaking and operated slowly until I lubed it. Unless it is corroded, your HCAC may only need to be lubricated. Use a very high temp lube like dry slide or anti seize. The valve is vacuum actuated and spring loaded in the opposite direction. Just connect any hand operated vacuum pump to the actuator and you can operate the valve to test it. Also make sure that you have no leaks at each end of the vacuum line that connects to the actuator. Concerning p0420, cat below efficiency: I could not drive 65 mph without setting code p0420. Code p0420 means the cat is dirty, not operating at full efficiency, but hopefully, not damaged. I could not afford to throw money away on a new cat or on o2 sensors unless it was absolutely necessary. So after some research, I decided should try cleaning my cat. I read that fuel additives that claim to clean the cat can overheat the cat and destroy it so I did not try them. I did find 2 safe cleaning methods online: News - BioEd Online using citric acid to clean the cat , and all over youtube, soaking the cat in soapy water. I cleaned my cat over thanksgiving weekend, 2012. I removed the exhaust system, only 4 bolts and 1 support. The hardest part was unplugging the rear o2 sensor located under the right front floor carpet. I removed the o2 sensor from the exhaust pipe. I inspected the cat. If it has chunks missing, it is done for. Mine looked good. I tried hot soapy water first. I used an electric griddle to heat my bucket full of soapy water and stuck the exhaust, cat end first into the bucket so that the cat was completely submerged. It stayed there, just below boiling temperature for 12 hours. I had to add more water several times and I agitated the exhaust up and down several times. I rinsed out the soap, reassembled everything, test drove, Failure! p0420 came right back. So, I tried again using the second method, but, I used 13 gallons of white vinegar in place of citric acid. They are very similar and white vinegar is easier to get than citric acid and vinegar is cheap. Same routine, soaked the cat in hot smelly vinegar for 8 hours. I stopped at 8 hours only because the white vinegar steamed off so fast that I ran short of vinegar after 8 hours. I removed the cat from the bucket. The cat looked great, no rinsing needed. But, the bucket and griddle looked pretty bad from exposure to the hot vinegar. Put the car back together, test ran, and no more p0420 code since thanksgiving 2012. The hot white vinegar worked for me. The hot soapy water may have loosened things up for the vinegar. I don't know for sure. But it was a good cheap fix for my p0420 issue.
Nope, my scangauge indicated that both o2 sensors were operating correctly, and the graphs showed that the cat was not operating correctly. When I removed the rear o2 sensor prior to cleaning the cat, the o2 sensor was clean, so I just reinstalled it later.
Okay, I am going to check out the O2 sensors and get the car on a lift again to check the HCAC. It feels like it is operating okay, but that was on a jack and it was cold and getting ready to snow. I like the idea of cleaning the Cat. A mechanic friend cannot believe it works. I sent him some links to check out. Thanks everyone. Will update once I get through this. tom in maine
Had the car on a lift today. We checked the O2 sensors on a scanner and they seem okay. They are functioning as they should. The first cat is working properly. The HCAC could be the issue? It is moving freely. We are going to do nothing. There is no emissions testing up here and the car is running fine. I have more questions though. If I unplug the HCAC, will it stay opened so it does not cause any problem? If we unplug the HCAC, plug the vacuum line and try running with the CEL reset, wouldn't the CEL stay off? Just trying to understand how the HCAC functions and its purpose. I still think there is some merit in reworking the exhaust without the HCAC. It might warrant a different second O2 sensor, maybe not. It would seem that two catalytic converters in series as in the Gen II is a possibility. It would be good to know that there are other options. I am going to do nothing at this point since there is no need to do anything. That is easy! tom in maine
I understand your decision to do nothing. If you later decide to do something, DTC P0420 points to the catalytic converter, not the HCAC. My first suggestion would be to replace the oxygen sensor upstream from the catalytic converter. A new, more responsive O2 sensor may allow the engine ECU to decide the catalytic converter is OK. A second step, given your Maine location, would be to find a muffler shop that can cut the existing catalytic converter out and weld an aftermarket unit in.
Also, someone posted about using white vinegar, heated, to clean the catalytic converter. It would be a cheap fix if you can confirm it works. Bob Wilson
I guess I am not quite making myself clear. A couple things are of concern and a bit confusing. My first step will be to replace the O2 sensors when that time seems imperative. The front one will require removing the pipe to get to it. I am thinking that if and when we take it down, we might consider reworking the system since I am already taking things apart. The car does have 320k on it and at some point something will warrant replacement. Dipping the front Cat in vinegar is a bit cumbersome given the pipe configuration. I suspect it will work, but a high quality replacement cat makes more sense. If we are installing that, there seems to be some merit in eliminating the HCAC. Considering that the HCAC is a problem area, it seems like a fun project (remember I do not have a lot tied up in this car) to try eliminating it and making it more like a Gen II system. If we redo the system and it works, then we have contributed to the common wisdom with a safe, perhaps relatively inexpensive alternative to the $1200 pipe. I am just trying to sort out how mission critical the HCAC really is since it is missing on Gen II. I can always come up with ways of finding how things do not work. I would like to make an informed decision as to if and when we do this. A $1200 replacement will not happen. Everyone agrees the HCAC is a stupid design, so it seems logical to replace it. My 2 cents worth. I do appreciate everyone's comments and guidance. tom
The only impact of removing the HCAC is that your car will emit a bit more emissions during warmup, and your check engine light will be continuously on.
Thanks Patrick. I wonder if a lower mass second cat would heat up faster and minimize that issue. Why would the check engine light be on? Both O2 sensors are before the HCAC. Thanks, Tom
I no longer own my 2001 or its repair manuals, but I believe that the HCAC has a sensor which detects whether the valve is open or closed. If the HCAC is gone then the sensor will no longer be connected to the engine ECU. The ECU will log a DTC and turn the check engine light on.
I will check that out. It would be an option to keep the actuator in place, perhaps at a better location so it still does it thing. I think we might have a weak second O2 sensor, so this will all wait for a better day, perhaps.
Gen 1s are getting old enough that there have also been some recent "thereifixedit"-style posts about just routing the vacuum actuator hose to a dummy actuator so the ECM thinks it is moving something, and doesn't set a trouble code.
