Codes P0420, P0300, P0301, P0304, P0440

1. I doubt that an oil change would cause a misfire (the P030x DTC) problem but it is easy enough for you to check the engine oil level.

2. When was the last time you had the iridium spark plugs changed? The service interval is 60K miles for Classic.

3. DTC P0420 means a failed catalytic converter which at your odometer reading is certainly plausible.

 

What does your Prius-aware scanner show for the O{1} and O{2} values?

Bob Wilson

 

As stated in the previous post, it could be O2 sensors telling your car the cat is bad.
I faced the same dilemma recently with my old car. My research showed quite a few aftermarket cats are only good for a couple years of inspection before they don't perform well enough. Magnaflow was rated pretty well out of the bunch from what I could gather. OEM is obviously best, but big $$.

 

I'm in the same predicament with my 01 classic needing to pass emissions test. Local tech showed me on the scanner how the downstream O2 sensor is indicating weak CC. I've already replaced both O2 sensors (and cleaned the throttle body, replaced 12v battery, air filter, iridium spark plugs, MAF sensor (for other recent DTCs))

As for the CC, have you found a reasonable resolution? I mean who wants to spend a grand on exhaust for a 13 y/o car that is now prone to mechanical issues? ... other than the fact that it sips gas.

Anyway, I'm trying to decide to go with OEM or aftermarket CC. Any info would be appreciated.

 

I think you should have an exhaust system shop install an aftermarket catalytic converter but that will require some welding. The original cc will have to be cut off and the replacement welded in, so that the HCAC valve which is upstream from the cc can be retained.

The HCAC valve is one reason why the correct Toyota catalytic converter is so expensive, since both are included in the one assembly.

Don't expect the aftermarket cc to last very long, but what do you expect for ~$300.

 

Roy from canada -- here is info from my service manual:

P0420

Catalyst System Efficiency Below
Threshold (Bank 1)
_ Gas leakage on exhaust system
_ Open or short in heated oxygen sensor circuit
_ Heated oxygen sensor
_ Three–way catalytic converter
_ _
P0440

Evaporative Emission Control
System Malfunction
_ Hose or tube cracked, hole, damaged or loose seal
_ Fuel tank cap incorrectly installed
_ Fuel tank cap cracked or damaged
_Vacuum hose cracked, hole, blocked,damaged or disconnected
_ Fuel tank cracked, hole or damaged
_ Charcoal canister cracked, hole or damaged
_ Open or short in vapor pressure sensor circuit
_Vapor pressure sensor
_ Fuel tank over fill check valve cracked or damaged
_ECM
_ _
P0441

Evaporative Emission Control
System Incorrect Purge Flow
_Vacuum hose cracked, hole, blocked damaged or disconnected
_ Open or short in vapor pressure sensor circuit
_Vapor pressure sensor
_ Open or short in VSV circuit for EVAP

VSV for EVAP

 

Roy from canada -

More info on po 420

DTC P0420 Catalyst System Efficiency Below Threshold
CIRCUIT DESCRIPTION
The ECM compares the waveform of the oxygen sensor located before the catalyst with the waveform of
the oxygen sensor located behind the catalyst to determine whether or not catalyst performance has deteriorated.
Air–fuel ratio feedback compensation keeps the waveform of the oxygen sensor before the catalyst repeatedly
changing back and forth from rich to lean.
If the catalyst is functioning normally, the waveform of the oxygen sensor behind the catalyst switches back
and forth between rich and lean much more slowly than the waveform of the oxygen sensor before the catalyst.
But when both waveforms change at a similar rate, it indicates that catalyst performance has deteriorated

 

Thanks Patrick and Roy for your replies and info. It's unfortunate that I had installed a inexpensive salvage exhaust (from a guy I know, rust free, 03, low miles) to resolve the P1436 issue, but I'm still getting P0420 for the cat. 2 bad cats? Hmmm. It's possible.
This may be beating a dead horse (or dead cat), but my understanding so far is that there're many variables concerning these emissions DTCs. Considering that I've already replaced the O2 sensors with OEMs, should I assume that a waveform comparison of the O2 sensors and a heat test of the cat are sufficient to conclude that the cause of P0420 is indeed a bad cat? Can a Toyota shop conduct any other diagnostics other than those above?
Just checking before I go into installing a new aftermarket cat, which from what I understand may not keep the CEL away for long.
I'm also considering selling this classic b/c my Gen II is so much more reliable and that is where I need to head from here.

BTW, I'm posting my 01 repair record on your Classic Prius Repairs survey thread.

Tom

 

Yes, if you have newly installed oxygen sensors the only other check I can think of is to hook up an oscilloscope to see that the upstream O2 sensor shows a rapid voltage fluctuation (which corresponds to the engine ECU operating in a feedback mode, continually varying the air/fuel ratio a bit rich then a bit lean.) The downstream O2 sensor should show relatively constant voltage which indicates the cc is doing its job. If you also see rapid voltage fluctuations from the downstream sensor then that is evidence the cc has failed.

The above assumes that you've driven at freeway speeds 20 miles or so to make sure the engine and the cc are fully warmed up.

 

If you buy the mini vic techstream $30 from the internet and a old computer with 32 bit xt installed you can view the oxygen sensor readings as you drive as well as the mass air function readings. If you do that I can give you readings from one of my 2001 prius cars to compare. This may be of some help.

Roy from canada

 

I replaced both o2 sensors and the MAF (mass air flow sensor) on one of my cars and the 420 code did not come back. You can but the MAF on the internet for under $30 (chinese made). I bought 3 and replaced the MAF sensors on all 3 cars (2 were working OK) and they perform as good as the originals.

 

Will any tech actually take the time to drive 20 mins on the freeway? The local tech did this while idling after I drove only 10 mins to the shop and it sat cooling for a while. He said he saw enough fluctuation in the d/s O2 sensor to indicate the cc is not working properly. Then checked the heat coming from the cc with a... lazor(?) That is it, for $74.

 

[QUOTE="royfrontenac, post: 2013441, member: 120862
I replaced both o2 sensors and the MAF (mass air flow sensor) on one of my cars and the 420 code did not come back.[/QUOTE]

Thanks. I did replace the MAF sensor recently for the P0171 and it didn't come back, but 0420 did.

 

I am not a mechanic, just a handyman with a garage so my help is limited to my repairs on my cars. I purchased the techstream software and cable off the internet and it allows me to see o2 readings as well as many other functions on the car. It sounds like you have replaced both o2 sensors and the MAF sensor the same as I did and still have the problem. Cannot be of much more help at this time.

Roy

 

Update: With both O2 sensors already installed, and cat. converter (CC) proving inefficient, I purchased an Eastern Echo II 40544 direct fit CC and had it mounted and welded on the output pipe. After clearing the code, completing the "drive cycle", ensuring the "ready state", with no further CEL, I passed the emissions test 23 Jun 14. Praise the Lord! Thanks to all who helped me out here too - I'm grateful for all of you.

BTW, I learned in the process that the sooner one resolves emissions problems (DTC's) upstream (air/fuel/electrical issues), the better chance of preventing damage downstream (O2 sensor and CC).