maybe o2 sensor?

[lax24]

i have a 97 3.8L town and country. code comes up for o2 sensor. sometimes i have some hesitation on highway but recently it has been a more violent jerking. plugs and wires only about a year old. i know i have an o2 sensor problem but do i have another problem with the jerking on the highway? in other words, is this jerking symptomatic with a bad o2 sensor?

[RIP]

Since you have a known O2 sensor issue, I would start there. There can be many possibilities. Jerking depends on the fail mode. What code are you seeing?

[lax24]

i'm getting a 21 code which is o2 sensor but actually i'm getting 2 21's...i was under the impression that the code system would'nt repeat any codes??? the codes are seperated by a 35 (cooling fan relay) which has already been replaced.

[RIP]

Ya that's a new one for me but, it may be happening because MIL code 21 can be generated by several different failures on either the upstream or downstream sensor (you have two sensors). MIL codes are good for a quick look to get an idea of the faulty system. "P" or scanner codes give you the whole story. MIL code 21 has 11 scanner codes associated with it. At the very least, a scanner code will tell you which sensor circuit is at fault. Autozone will connect a scanner and tell you what codes you have for free. Some other parts shops do the same.

[lax24]

well, i replaced the downstream o2 sensor and have not had any trouble for about a week. honestly, i can't believe the downstream sensor would cause that kind of problem. but so far so good...i'll keep my fingers crossed. thanks.