2000 Chevy Cavalier O2 sensor code

2000 CHEVROLET CAVALIER
138,000 MILES • 4 CYL • FWD • AUTOMATIC
Avatar
MULLIGANSTEIN
  • MEMBER
  • 21 POSTS
OBDII code was: PO420 MOD$10
catalyst system efficiency below threshold
Bank 1
I replaced the downstream sensor but the code came back. Can you give me a lesson on O2 sensors and the Cat so I can try to pinpoint the problem without throwing too many parts at it.
My next step would be to replace the upstream sensor, but it is reading a steady 900 mv.
Also, what is Bank 1 and what does that mean?
What is Mod$10?
Perhaps the first 3 or 4 places to look with regards to this model number, engine size, age, mileage etc....
Thanks very much for your help.
Oct 5, 2010 at 7:55 PM
Advertisement
Avatar
BLACKOP555
  • CERTIFIED EXPERT
  • 10,386 POSTS
bank one sensor one is referred to as the sensor before the catalytic converter on the side of the engine that the #1 cylinder is on. it is used for fuel corrections

it should be CONSTANTLY switching between .1v and .9v. if the o2 sensor is getting bad it will stick at a random voltage and barely switch. sounds like that is whats happening with your vehicle. if the sensor reads improper the bank 1 sensor 2 will read faulty as it compares its readings with #1. if the #1 isnt switching and the #2 is even slightly switching the computer interprets this as a failing catalytic convertor
Oct 5, 2010 at 9:54 PM