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2004 Cadillac P0420 Code

Tiny
PMASPKS
  • MEMBER
  • 2004 CADILLAC DEVILLE
  • V8
"Catalyst System Efficiency Below Threshold (Bank 1)". Is this something I can repair myself? I have already changed out all sensors, replaced the catalytic converter, and had the torque converter replaced, now this pops up after about 250 miles.
Sunday, December 12th, 2010 AT 1:12 AM

2 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Go to this link: https://www.2carpros.com/trouble_codes/obd2/P0400
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Sunday, December 12th, 2010 AT 1:20 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
It's pretty rare that this is caused by anything but a bad converter. The criteria for setting it is that the front and rear 0/2 sensors have to pretty much mirror each other among other things and that won't happen if the cats are working. I did see it happen once from a crack at the front of the converter letting 0/2 in.
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Sunday, December 12th, 2010 AT 1:31 AM

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