[RobertB]

There are quite a few threads dedicated to these codes. Seek(search) and ye shall find. But here is a short summary...

P0442 and P0446 are Evap system codes. Many people get these from leaks in the Evap system. On my Sienna it was a leaky canister. Have your system smoke tested for leaks. Did you use an OEM Toyota gas cap? An aftermarket cap may not properly seal. If you have a high mileage Sienna or drive in salty ice roads, it is likely that your canister has a leak by now.

P0420 is set when the catalyst system is deemed (by the ECU) to be below threshold. ECUs on 2001-03 were defective and set the code when the catalyst was often still good. P0420 can be caused by a number of other issues. To eliminate the code, some have replaced the pre-cat O2(actually AF) sensors. Others have replaced the rear O2 sensor. Exhaust leaks around the pre-cats/cats can also cause this problem. The main rear cat or one of the pre-cats could be below threshold too. Toyota will want to sell you either an updated ECU for $1500, a pre-cat y-pipe, and/or a main cat for about $1500. If you try a shotgun approach and replace O2 sensors, only use OEM Denso. If you buy cats, only buy OEM Toyota cats unless you have upgraded your ECU(on 2001-03). If you get the corrected ECU, you can then use cheaper aftermarket cats.

 

[RobertB]

I posted more info about the ECUs on the Toyota Nation forum earlier today.... but since you asked about ECUs from a salvage yard, I'll address that here. Yes, you can get one from a salvage yard, you would need part number 89661–08081 or 89661–08082. 89661–08082 is the very latest version of it, but 89661–08081 should have the cat update too. The biggest problem in getting a used ECU is finding one first! The next issue, is making it work in your Sienna. If your Sienna does not have an immobilizer, and the salvaged Sienna also does not have an immobilizer, then you just plug it in and go. If the salvaged ECU came out of a Sienna without an immobilizer, yet your Sienna has one, you have to program the keys in when you install it. There is a procedure to do this. I didn't have to do it on mine as I do not have an immobilizer. A locksmith might help with that if needed. It gets really tricky if the salvaged ECU came out of a Sienna with an immobilizer. In that case you have to reprogram the 93C56 chip in the ECU back to a "virgin" state. This is not rocket science, but you have to have a method to reprogram that chip. You usually have to remove it from the motherboard first to program it. This requires a soldering iron with a fine point and a desoldering tool. Then you attach an SOIC8 clip to it and download the new data to it. It is a tiny surface mount chip with 8 pins. It only holds 256 bytes of transponder codes from the keys of the salvaged Sienna. I have published the values for what it took for my 2001 Sienna somewhere on the forum. But if you want to go that route, I can find and post them again.

To tell if you have an immobilizer, look at your keys. If a fully metal key will start the car, it does not have an immobilizer. If the key has a plastic cover with an embedded transponder then you do have the immobilizer. I think there might be a red dot on it where the transponder slides into the plastic. I don't have one to look at however.

The A/F sensors have a code for the heater circuit failure which is separate from the other Cat system codes. However, they can get "lazy" with age. There is a resistance check that can be performed. But it probably would have thrown the code if that had already failed.

 

[RobertB]

It can take a while to trigger a P0420 if you are driving short distances. Ours was being driven only about 15 minutes at a time. This wasn't usually enough to trigger the Cat test in the ECU. But if you can get the Evap problem fixed, that would give you time to fix the catalyst issue. I think I paid somewhere around $500 to 600 to have the canister replaced 6 or 7 years ago. I would do it myself now.

Oh, I also have a Bosch O2 sensor, and Denso AF sensors. The Bosch works fine. If I had to do it again, I would have bought a Denso for more perfect OEM compatibility.

 

[RobertB]

Excellent! That takes the pressure off... and allows you to try some simple fixes first.