# 2000 Lexus Diagnostic Code #P0420 (Chk Engine Light is on) **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** lexus, 300\ **Created:** [May 28, 2010, 3:02pm UTC](https://community.cartalk.com/t/2000-lexus-diagnostic-code-p0420-chk-engine-light-is-on/49502 "2010-05-28T15:02:14Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![STP007](https://avatars.discourse-cdn.com/v4/letter/s/e0b2c6/32.png) [@STP007](https://community.cartalk.com/u/STP007)\ **Post date:** [May 28, 2010, 3:02pm UTC](https://community.cartalk.com/t/2000-lexus-diagnostic-code-p0420-chk-engine-light-is-on/49502/1 "2010-05-28T15:02:14Z")
Auto scan reads code P0420 - "Catalyst Efficiency Below Threshold, Bank 1. Is this an oxygen sensor? I’m told there are three in the exhaust. Can I further isolate this or should I take the car to the dealer? ---
**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\ **Post date:** [May 28, 2010, 3:39pm UTC](https://community.cartalk.com/t/2000-lexus-diagnostic-code-p0420-chk-engine-light-is-on/49502/2 "2010-05-28T15:39:33Z")
The code is refering to the catalytic converter efficiency. Here is a link to some info on the code. > **[P0420 Catalyst System Efficiency Below Threshold](https://www.obd-codes.com/p0420)** > > How to diagnose, repair, and info on symptoms and causes of a P0420 engine code which means the catalytic converter is no longer performing at a normal level. ---
**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\ **Post date:** [May 28, 2010, 5:17pm UTC](https://community.cartalk.com/t/2000-lexus-diagnostic-code-p0420-chk-engine-light-is-on/49502/3 "2010-05-28T17:17:13Z")
It is the rearward oxygen sensor that generated the signal that caused the CEL to come on and threw the P0420 code…Oxygen sensors have a design life of 100K miles. My Crown Vic threw this code at 160K miles. I replaced both the rear sensors (left and right bank), reset the light and it has remained off… I suspect the DEALER will try to sell you both CATS, and all the oxygen sensors generating a repair bill approaching $3000… The mileage on your car would be helpful ---
**Author:** ![STP007](https://avatars.discourse-cdn.com/v4/letter/s/e0b2c6/32.png) [@STP007](https://community.cartalk.com/u/STP007)\ **Post date:** [May 28, 2010, 8:37pm UTC](https://community.cartalk.com/t/2000-lexus-diagnostic-code-p0420-chk-engine-light-is-on/49502/4 "2010-05-28T20:37:46Z")
Thx for the good feedback. My car has 120k miles. To date I have replaced the bank 1 sensor and the MAP sensor.