How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Jan Andersson Your Own Question

Jan Andersson
Jan Andersson, ASE Master Tech
Category: Toyota
Satisfied Customers: 815
Experience:  20 years of auto repair and racing both in Europe and USA. Have had Toyotas before and love them!
18975528
Type Your Toyota Question Here...
Jan Andersson is online now
A new question is answered every 9 seconds

2002 Toyota Prius: The check engine light came..stalling

Resolved Question:

The check engine light came on on my 2002 Toyota Prius. When I hooked up my diagnostic tool I got the code P0420 which is something about the Catalytic Converter system not performing at peak efficiency. (I know this is not the exact wording for the problem but you get the general idea I think) The car seems to be running just fine, starts fine, no stalling or any other mechanical issues that I can detect. Unless this is a super serious issue I am not planning on doing much with this at this time but I would like to know what effect if any this could have on my cars engine. I should tell you that the car currently has about 325,000 miles on it.
Submitted: 4 years ago.
Category: Toyota
Expert:  Jan Andersson replied 4 years ago.

Hi,

 

here's the description for the code

 

 

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

 

 

There are two O2 sensors in your exhaust system. One measures exhaust gases before the catalytic converter, and the data is used by the engine management system to adjust the fuel feed. The second, "downstream" O2 sensor is locates in the exhaust pipe after the catalytic converter, and it is used only to monitor the efficiency of the converter, by comparing the values between the two sensors. Because the converter is between the two, the later sensor should detect much cleaner exhaust gases if the converter is working right.

 

With time, two things inevitably happen: the converter efficiency goes down, and the sensor accuracy is reduced or it stops working.

 

So... your computer is telling you that the second sensor is reporting insufficient operation of the catalytic converter. The real cause is either just that, a failing converter, OR a failing sensor reporting wrong values.

 

I would first replace the O2 sensor, because they have a shorter lifespan than the converters. If the problem repeats, then you need a new converter. Usually when you replace a converter, you should replace the O2 sensor(s) too. But this way you already have a new one in there. With luck, the O2 sensor is all you need. With bad luck, you also need the converter. This is a logical way to approach it and it starts with the lowest cost repair first.

 

This code cannot be a result of a loose gas cap. Other codes can, and Double checking the gas cap was a good move though, a first step when the light comes on. Most people don't think about it or know about it.

 

The problem is not critical. The catalytic converter is just getting worn, and not cleaning the exhaust gases as good as it should. In somewhat rare cases they can start crumbling and clogging up internally, and then they can cause driveability problems due to restricted exhaust flow. You are not there yet. Your only problem now is increased emissions. The car won't pass emissions testing.

 

 

Jan Andersson, ASE Master Tech
Category: Toyota
Satisfied Customers: 815
Experience: 20 years of auto repair and racing both in Europe and USA. Have had Toyotas before and love them!
Jan Andersson and 8 other Toyota Specialists are ready to help you

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • THANK YOU, THANK YOU, THANK YOU!! I've got my baby back. Tomorrow I will get a tank of high octane, remove the top, go for a long long ride and enjoy my car. THANK YOU! Jughead USA
< Last | Next >
  • THANK YOU, THANK YOU, THANK YOU!! I've got my baby back. Tomorrow I will get a tank of high octane, remove the top, go for a long long ride and enjoy my car. THANK YOU! Jughead USA
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
  • Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
  • Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland
 
 
 

Meet The Experts:

 
 
 
  • Chris (aka-Moose)

    Auto Technician

    Satisfied Customers:

    278
    16 years of experience
< Last | Next >
  • http://ww2.justanswer.com/uploads/MU/muddyford/2012-6-13_1204_1.64x64.png Chris (aka-Moose)'s Avatar

    Chris (aka-Moose)

    Auto Technician

    Satisfied Customers:

    278
    16 years of experience
  • http://ww2.justanswer.com/uploads/EU/eurotec/2012-6-11_13153_mpjaphoto.64x64.JPG Marty's Avatar

    Marty

    ASE Certified Technician

    Satisfied Customers:

    167
    ASE & Bosch Master Tech. 30 years experience.
  • http://ww2.justanswer.com/uploads/AM/amedee/2013-10-24_23656_Amedee1.64x64.jpg Amedee's Avatar

    Amedee

    Toyota Technician

    Satisfied Customers:

    1132
    ASE Master Technician advanced level specialist. Wisconsin certified emissions state inspector
  • http://ww2.justanswer.com/uploads/CA/caprio23/2014-4-30_201741_20121205122939.64x64.jpg Anthony's Avatar

    Anthony

    ASE Certified Technician

    Satisfied Customers:

    373
    ASE Master Automobile Technician with over 20 years exp. in this field.
  • http://ww2.justanswer.com/uploads/CR/crzydrvr00/2013-11-3_12123_246347.64x64.jpg Richard's Avatar

    Richard

    ASE Certified Technician

    Satisfied Customers:

    9
    Toyota tech. ASE Certified Technician
  • http://ww2.justanswer.com/uploads/SK/skyvisions/2012-6-9_23736_JACropped3.64x64.jpg Skyvisions's Avatar

    Skyvisions

    ASE Certified Technician

    Satisfied Customers:

    11403
    Toyota Master Diagnostic
  • http://ww2.justanswer.com/uploads/genchigenbutsu/2009-05-09_003043_cimg16431.jpg Genchi Genbutsu's Avatar

    Genchi Genbutsu

    Toyota Master Technician

    Satisfied Customers:

    3425
    Toyota Certified Master Diagnostic Technician, ASE Master Technician with L1 Advanced Engine
 
 
 
Chat Now With A Toyota Mechanic
Jan Andersson
Jan Andersson
Master Tech
89 Satisfied Customers
20 years of auto repair and racing both in Europe and USA. Have had Toyotas before and love them!