1997 Mazda MX-5 Miata Long-Term Road Test

  • Full Review
  • Pricing & Specs
  • Road Tests
  • Comparison
  • Long-Term (10)

1997 Mazda MX-5 Miata: Pulling the Codes

April 30, 2013

1997 Mazda MX-5 Miata

Project Miata's check engine light is on. This is the code that came up: P0420.

P0420 is a catalyst efficiency code. This could mean that our cat's not functioning properly, or an oxygen sensor is on the fritz or even something else.

But I suspect the cat. Project Miata has gradually been feeling slower lately and running sorta grumpily. All of those things point to a toasted cat. I'll check that first.

Jason Kavanagh, Engineering Editor

Comments

  • ampim ampim Posts:

    It's most likely the cat. O2 sensors have their own diagnostic algorithms. If it was the sensor, then you'd get a sensor code. Most ECU's will intentionally change up the A/F and watch for the post-cat O2 sensor to see how much the cat cleans up the exhaust. If it's too dirty, then it'll set a code, or it might set it after a number of failed tests. If you haven't taken it on a long (30+ min) sustained drive at highway speeds in a while, try that. The extra heat in the cat will sometime clean up the matrix of material in there and allow it to do it's job. I've had similar problems with my RX-8.

  • ampim ampim Posts:

    It's most likely the cat. O2 sensors have their own diagnostic algorithms. If it was the sensor, then you'd get a sensor code. Most ECU's will intentionally change up the A/F and watch for the post-cat O2 sensor to see how much the cat cleans up the exhaust. If it's too dirty, then it'll set a code, or it might set it after a number of failed tests. If you haven't taken it on a long (30+ min) sustained drive at highway speeds in a while, try that. The extra heat in the cat will sometime clean up the matrix of material in there and allow it to do it's job. I've had similar problems with my RX-8.

  • I thought 420 meant smoking in progress? Wait, sorry, wrong topic.

Leave a Comment

Research Models

ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT
Have a question? We're here to help!
Chat*
Chat online with us
Email
Email us at help@edmunds.com
*Available daily 8AM-5PM Pacific