# O2 Sensors - 2000 model year **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** toyota, 4runner\ **Created:** [January 26, 2010, 12:40am UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234 "2010-01-26T00:40:34Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![rockyt](https://avatars.discourse-cdn.com/v4/letter/r/8491ac/32.png) [@rockyt](https://community.cartalk.com/u/rockyt)\ **Post date:** [January 26, 2010, 12:40am UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234/1 "2010-01-26T00:40:34Z")
Does anyone have solution or suggestion on a bank II code coming up when I’ve already replaced three of our O2 sensors and one of the two cat converters? Seen more than one mechanic since last year and check engine light still on. Have run techtron and premium gas after light reset but it still comes on after a day or so. I don’t want to keep paying mechanics to guess and spend more money and not fix the problem. ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [January 26, 2010, 11:23am UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234/2 "2010-01-26T11:23:02Z")
What is/are the actual code(s) that you get? There are lots and lots of codes that involve bank 2 and might have someone wondering about cats and o2 sensors. Report the actual number as in P0123 ---
**Author:** ![Manolito](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/manolito/32/3070_2.png) [@Manolito](https://community.cartalk.com/u/Manolito)\ **Post date:** [January 26, 2010, 2:51pm UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234/3 "2010-01-26T14:51:16Z")
Have you noticed a pattern of when the light comes on? I had a car that would set an oxygen sensor code only occasionally and only under very light load. Turned out it had a poor connection in the circuit carrying power to the heater in the oxygen sensor. Of course, it always worked fine when it was in the shop being diagnosed (grrrrrrr). Took months to figure it out. ---
**Author:** ![rockyt](https://avatars.discourse-cdn.com/v4/letter/r/8491ac/32.png) [@rockyt](https://community.cartalk.com/u/rockyt)\ **Post date:** [January 27, 2010, 12:50am UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234/4 "2010-01-27T00:50:41Z")
Last year the check engine light would come on in cold winter when refueling. By spring time the light wouldn’t come on at all. Now with O2 sensors replaced and 1 cat it takes longer for engine check light to come on. The longest period was 2 days and it no longer ties in to refueling. We weren’t always using higher octane gas. Light is always on until a mechanic resets it but it doesn’t stay off. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [January 27, 2010, 12:53am UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234/5 "2010-01-27T00:53:57Z")
Are you running the engine while refueling? If so, this will not only trip the light but is also dangerous and in some states illegal. ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [January 27, 2010, 12:59am UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234/6 "2010-01-27T00:59:40Z")
I’m still wondering what the codes are. ---
**Author:** ![rockyt](https://avatars.discourse-cdn.com/v4/letter/r/8491ac/32.png) [@rockyt](https://community.cartalk.com/u/rockyt)\ **Post date:** [January 27, 2010, 1:00am UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234/7 "2010-01-27T01:00:34Z")
No, we never run the engine while refueling - too dangerous and no need to keep car running. Someone at work suggested I try a new gas cap since old caps can set of the check engine lights if it’s not a tight seal. ---
**Author:** ![rockyt](https://avatars.discourse-cdn.com/v4/letter/r/8491ac/32.png) [@rockyt](https://community.cartalk.com/u/rockyt)\ **Post date:** [February 9, 2010, 12:58am UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234/8 "2010-02-09T00:58:24Z")
I finally got the codes: PO420 Bank 1 cat inefficiency, EGR monitoring ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [February 9, 2010, 1:24am UTC](https://community.cartalk.com/t/o2-sensors-2000-model-year/43234/9 "2010-02-09T01:24:11Z")
I’m not sure where the EGR monitoring part comes from, but the P0420 is about the catalytic converter - although it doesn’t necessarily mean that you have a bad cat (maybe). Ironically, it is possible that you’ve been replacing O2 sensors just b/c they were working properly, although it is possible for a bad sensor to be involved. Check this out: [http://www.obd-codes.com/p0420](http://www.obd-codes.com/p0420)