Buy Now | Log In | ALLDATA Corporate Site |
Back To Home Page
Log In To Your Subscription
Go To ALLDATA Back Home
Buy A Subscription! Back Home About ALLDATA Information View Sample Vehicles Read Testimonials Frequently Asked Questions Contact Us
Dowload Our Navigation Chart

Sign Up To Receive Alerts

Click Here to receive regular product updates, special offers, and automotive news.

2012 Subaru Now Available May 2013: More 2012 Vehicles Added including Fiat!
• View New Vehicles
2012 Subaru Now Available December 2012: More 2012 Vehicles Added including Chevy & GMC!
• View New Vehicles
View All News and Updates:
• Go To News
Tech Tips
  Read All Tech Tips

ALLDATA Tech Articles Are Updated Weekly
• View All Tech Articles

  Dodge Durango: Brake Pulsation Problems In Paul's Durango
• Read Dodge Article
Fixing A Smelly Audi Audi Tech Tip: A4 begins to Smell caused by a Faulty Hose Composition
• Read Audi Article
Why Do You Need To Change Your Timing Belt? Why Replace Your Timing Belt
• Read Belt Article
Jim Grant Tech Tips Jim Grant Tech Tips
A collection of helpful articles based on reader submissions
Home >> Featured Tech Articles >> Go Back
  Jim Grant's Tech TipsJim Grant's Tech Tips
Below is a collection of Jim Grant's Tech Tips sorted by Vehicle Make. These Tech Tips were answers to questions submitted to Jim by users over the course of many years.
If you have any questions, please feel free to email us.



Lincoln - Mercury
  Jim Grant's Tech Tips

'01 Toyota Corolla, Emission Code P0420

Q: I own a ‘01 Toyota Corolla with an emission code P0420 for catalyst system fault. Where should I start? I’ve already erased the code and it has returned.


A: Your vehicle has 2 oxygen sensors. One is mounted in front of the converter and used primarily for monitoring and fine-tuning of the fuel to the engine. The second oxygen sensor is mounted behind the converter and is used mainly to monitor the efficiency of the converter. While you’re driving your vehicle down the road at just the right speed, time and temperature the computer takes a look at the 2 oxygen sensors and compares their values. If the 2 sensors match up too closely the computer will throw a flag and turn on the check engine light. You have to remember that the oxygen sensor in front of the converter has exhaust gases that are ripe from the engine. The second sensor is after the converter and if the converter is working correctly this sensor will be reporting less information, it won’t be as active, because the converter is using the remaining oxygen to clean the exhaust. What your computer is reporting is that the 2 sensors are looking too much alike. You just may have a bad converter. But don’t jump there just yet. There are a couple of other conditions that can falsely set this code and you do not want to replace that expensive converter just to have the same code return. First there can be no exhaust leaks. If there are fix them. The heater circuit or the heating element in the sensor behind the converter has to be checked. Yes there is a heater in the oxygen sensor. The heater is used to get the oxygen sensor hot and functioning quickly to reduce exhaust emissions. If the wiring to or the heating element itself is bad you can get a false converter code. So that part of the system must be diagnosed and repaired if needed before the converter is deemed inefficient. It gets back to that just because the computer says so, doesn’t mean it’s true stuff.!

Have any Questions About Please Email Us
Buy Now | Log In | About | Sample Vehicles | Testimonials | Join Affiliate Program