P0420 downstream is fluctuating?

Tiny
AKORD
  • MEMBER
  • 1999 HONDA ACCORD
  • 2.3L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 150 MILES
The upstream sensor is steady, and the downstream is fluctuating. Is that considered a bad catalytic converter?
Image (Click to make bigger)
Thumb
Sunday, March 15th, 2026 AT 11:19 AM

1 Reply

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 55,141 POSTS
Yep, you nailed it, the catalytic converter is probably bad. You can help confirm this issue by checking out this video.

https://www.youtube.com/watch?v=kNXh1Lphzr4&pp=0gcJCcUKAYcqIYzv

Please go over this guide and get back to us.
Was this
answer
helpful?
Yes
No
+1
Monday, March 16th, 2026 AT 10:10 AM

Please login or register to post a reply.

Related P0420 Content

VIEW MORE