Chrysler Repair: Service Engine code 12, 21, steam radiator, obd ii

Question
QUESTION: Hi, I too have a 97 JXI Chrysler Convertible (with the Mitsu 6 cyc) service engine light on it runs fine...the key on key off method gives me : 1-2-2-1-2-1 then the 5-5.  I cant figure out how to get this down to a 2 position code.
Thankx
Mike

ANSWER: Hi Mike,
The 12 code says the battery power to the pcm was disconncted sometime in the past 50-100 key cycles. If you knowingly disconnected the battery then that code can be ignored.
Unless by reading it again you come up with something other than two 21 codes in a row we just have to assume the same problem was detected twice. That 21 code means the the oxygen sensor on the the exhaust manifold is not getting a signal to the pcm, either because it failed or because the wires (which are fragile) have been compromised. So inspect the sensor and its wires and consider replacing it. The engine may run well but the economy and the pollution level will be affected. The 55 of course means 'end of readout'. So take another look and see if there might be a different pattern than 2-1-2-1.

Roland

---------- FOLLOW-UP ----------

QUESTION: Thanx Roland I will check out the o2 sensor...can you tell me where it's located? I see a sensor sticking out of the side of the intake manifold (looks like an old fashioned accordion steam radiator) on this thing...Is that it?  ALso, do I clear the codes by disoconnecting the battery? wouldnt that give me the 1-2 error again?

Answer
Hi Mike,
There are two possible sensors: an upstream mounted on the side of the front exhaust manifold, and the downstream that is mounted on the output of the catalytic converter. The 21 code doesn't tell you which one is bad, so you would do well to get an OBD-II readout with a plug-in reader that attaches to the plug under the dash next to the steering column. The upstream code would be in the 0130's range and the downstream in the 0150's range. An Autozone parts store will often do the readout for free.
Once you decide which one to replace I would then soak the threads of with penetrating oil overnight, and then warm up the engine the next day before trying to remove it. It will look just like a spark plug but have 4 delicate wires connected to the top of it and a disconnect plug nearby.
Yes, if you erase the codes by disconnecting the battery you will still get a 12 code which will last until 50-100 key on-off cycles then self-erase.
Roland