P0420 engine code baffles Toyota

This doesn't answer your problem but you can get away with a failed inspection in New York under certain circumstances - since you have spent over $450 in trying to repair the emissions system. You can get a waiver:

What can occur if my vehicle fails the OBDII test?
If the NYVIP requires a vehicle to receive an OBDII emissions inspection, and the vehicle does not qualify for a waiver (see below), the vehicle must pass that inspection in order to receive an inspection sticker. The failure of the vehicle to pass the inspection can prevent the renewal of the vehicle registration. See the information about registration-based enforcement of the emissions inspection requirements. You must have the vehicle repaired to meet the standards and pass a reinspection.
Inspection Waiver. A vehicle that is required to have the OBDII inspection can qualify for a waiver if:

• The vehicle fails the OBDII inspection, but passes the safety inspection, the gas cap check, and the visual inspection of the emission control devices, and
• The vehicle receives repairs that are related to the failure of the OBDII inspection and the cost of the repairs is at least $450, and
• The vehicle does not pass the OBDII inspection during a reinspection.

The waiver is valid for one year.
After the reinspection, the inspector enters the repair information that you provide into the NYVIP equipment. The NYVIP equipment then notifies the inspector if the vehicle qualifies for a waiver. If the vehicle qualifies, the inspector can use the NYVIP equipment to print a waiver form. You must sign the waiver form, and the inspector must sign the waiver form. The inspection station keeps the waiver form and other documents related to the waiver. The inspector then issues your inspection sticker, and the sticker is valid for one year.
To qualify for a waiver:

• You must have the inspection report from the original NYVIP inspection station.
• The inspection report must show that your vehicle failed the original OBDII test, but that your vehicle passed the safety inspection, the gas cap check, and the visual inspection of the emission control devices.
• The emissions control system of your vehicle must be intact. The system must not show any evidence of tampering.
• You must have work orders and receipts that prove that repairs related to the vehicle emissions system were completed at a NYS-licensed repair shop. The work orders and the receipts must prove that the cost of the repairs, parts and labor, was at least $450. If you complete the repairs yourself, the calculation of the cost of the repairs includes only the cost of the parts that were used and does not include any amount for your labor.

 

Once cleared, how long before the code reappears? If I had some time I'd reset the computer just before inspection & hope.

 

Hi Tom,

What is the part number of the engine ECU that you installed? Ideally it should be 89661-47054. If it is 89661-47030, this is the problem.

When replacing the oxygen sensors, did you use Toyota parts? This is especially critical with regard to oxygen sensor #1 which is upstream from the catalytic converter.

Have you seen TSB EG017-03? If not, it is relevant to your problem and I attached it below.

What is the odometer reading on your vehicle?

It would be interesting if you could verify the voltages coming off the two oxygen sensors to confirm your dealer's finding that the catalytic converter is working properly.

 

Hi Tom,

Note that your profile indicates that your car is a 2001, that is why I thought the TSB might be applicable.

Another question: what did the catalytic converter rebuild involve? Was the old catalytic converter cut off and a new one welded in place so that the old HCAC chamber and the exhaust tubing was retained? Or was the rebuild less involved than that?

The reason I asked about the O2 sensors is because the engine ECU is quite sensitive to monitoring the proper voltages. Consider how the ECU determines if the catalytic converter is working or not. It expects the voltage from oxygen sensor #1 to rapidly fluctuate up & down to show that the feedback loop is working and that the Prius air/fuel mixture is oscillating up & down between lean and rich mixture. It expects the voltage from oxygen sensor #2 to stay relatively constant to show that the catalytic converter is "adding value" and not just passing the exhaust gases without processing.

When I owned my 2001 I had the Ecrostech miniscanner connected to that vehicle. Two of the parameters that I monitored were the O2 sensor voltages. Sensor #1 produced voltages ranging from 0.1V to 0.9V, quickly moving up & down. Sensor #2 produced voltages around 0.5V to 0.7V.

Since you have the correct engine ECU installed, my guess is that the catalytic converter or oxygen sensor #1 is operating marginally; hence DTC P0420 is being posted.

 

did the new cat pipe come with the shutoff valve in the middle of it?
a code p0420 absent other codes is almost exclusively a cat problem- with the exception of a few ecu issues.

how long does the code take to recur once it's cleared?

ummmm... starting to reach here, but any holes in the exhaust?

 

My car: 2001 125k miles on it. Code P0420 detected last week. Was told to replace cat. Dealer said that there are different OBDII codes for the 2 O2 sensors. I have read every post in this forum and it seems to me that there are NO CODES for the sensors and that the sensors need to be tested separately. Is this correct?

 

It sounds like those techs have forgotten how to do basic catalyst
tests by watching waveforms -- it's even all spelled out in the
service manual. Take the car to another service center if
you can... or get an independent to work with you on it, partially
in exchange for their learning about how to deal with Priuses. On
a Classic, this stuff can be watched by tapping ECU leads and not
even having to get under the car at first.
.
_H*

 

Thanks Hobbit. Person who gave me a lecture was NOT the actual technician but the front desk clerk. I will go elsewhere to try to avoid the expense of replacing CAT.

 

Do you have to add oil between oil changes? If so you are burning oil which ruins the Converter. Catalytic Converter clearn and then oil additive to prevent oil burn could solve this.

 

Don't know to whom you're addressing your question, but the OP hasn't been on PC for over 9 years and this thread has been dead for nearly 10 years.

 

This is very helpful thanks