Does anyone know what codes 12 and 21 mean? I know i need to replace the fuel pump and filter, and i'm curious what else needs to be done to get her running nice nice again. Please, any help would be appreciated. Thanks

'96 Plymouth Neon
SOHC ATX
within the last 5 months:
starter
battery
copper plugs & mopar 7.5 mm wires
head & oil pan gaskets
timing belt & tensioner
left outer tie rod end
front right hub and bearing

Code 12 is direct battery input to PCM was disconnected within the last 50 key-on cycles.
Code 21 is 02 sensor problem (oxygen sensor), upstream or downstream. You will need to get the "P" code to figure out which one it is, but more than likely it is the upstream.

Changing your PCV valve and air filter might help your car run a little better also.

Code 12 is direct battery input to PCM was disconnected within the last 50 key-on cycles.
Code 21 is 02 sensor problem (oxygen sensor), upstream or downstream. You will need to get the "P" code to figure out which one it is, but more than likely it is the upstream.

Changing your PCV valve and air filter might help your car run a little better also.

Thanks for the info, i knew there was something wrong with the O2 sensor(s), got a code a while back when my friend scanned it, but it dissappeared, and even the dealer said they couldn't find the code. The air filter's still good, but i do have a pcv valve in the trunk that i haven't had time to put in, guess i should get on that.