Your 1997 will be OBD-II, and codes for that can either be two-digit numeric or the "P-codes" (actually, there's P, B, U, as I recall. P being Powertrain, B being Body, U being Network. The second digit should be "0" or "1" - 0 being SAE standard codes, and 1 being vendor-speficic codes. The other three digits are specific system and error.) The OBD-II codes may also be listed as hexadecimal values (0-9 + A-F being digits,) but this is uncommon. You'll usually see them as a two-digit decimal value, or taking the format "Xyyyy" as given earlier.
You can check the codes I have listed on my site in the Tech archives - they're all culled from FSMs as I acculmulate them. OBD-II codes are listed in order by two-digit ChryCo code, but the two-digit code is also listed. Let's see...
12 - Direct Battery Input to PCM disconnected in the last 50 ON/OFF cycles. If you've done a service that required electrical disconnect recently, had to change your battery, or the tech pulled the battery leads (for whatever reason,) this is a normal code. DFWAI, unless you have other electrical problems
23 - Intake Air Temperature (IAT) Sensor supply voltage out of limits. This means that the +5VDC that the PCM supplies to the IAT (which then gets reduced by the IAT as the internal resistance changes to due air temperature) shows an "out of range" on the internal reference voltage comparator. This is likely to be a wiring fault, dirty connection, or something like that. Trace the wiring back from the IAT sensor as far back as possible, clean any connections, and visually inspect the wiring. Clear codes and see if it resurfaces.
55 - Completion of DTC display on CEL/MIL. This is a "closing code" to tell you it's done. If you were to check the CEL/MIL with
no faults present, Code 55 is all you'd get ("I have nothing to report.")
Since 12, 23, and 55 aren't listed as Hex values in the table, I am forced to presume that they would be invalid as hexadecimal DTCs, and therefore went to the decimal values. If you were reading codes in hex, DTC 55 does not exist (nor is there an Xyyyy SAE equivalent.) Likewise DTC 12.
ACTION PLAN:
Ignore DTC 12. Clear it, or wait for it to clear on its own. It is not a 'hard' code, and will not trip a CEL/MIL on its own.
Ignore DTC 55. It's just telling you "End of Report."
Check wiring,
et al, to evaluate possible causes of DTC 23. Also, be sure to check the source voltage to the TPS at that point - with the harness connector removed from the sensor and the key ON, you should see +5VDC at one terminal (of the harness socket) and 0VDC at the other. I can't tell you which colour of wire you should see +5VDC (nominal) at, but someone else probably has an FSM in your year to hand. If one of the wires is black, that will probably be the ground (and you should
not see +5VDC at that one. You should get it at the other one.)
Once you've gone through the wiring, clear the codes (any decent code reader should be able to do that for you - you can get a decent unit for under $100 with little to no effort. Check Sears...) and monitor.
It's not a bad idea to check for DTCs every year or so, even if you don't see the CEL/MIL lit. Why? Because there are 'hard' codes (light CEl/MIL) and 'soft' codes (no CEL/MIL) - so you won't know about a 'soft' code until something comes up. DTC 12 is a "soft" code - you only knew about it because DTC 23 tripped the CEL/MIL. DTC 55 is a "null" code - it only comes out when the system is interrogated to begin with.
Good luck!
Oh - and here's the listing of DTCs I've gathered so far -
http://www.kelleyswip.com/obd2.html. Note the green field for about 1/5 of the entries ('soft codes') and the red field for the rest ('hard codes.')
