Getting rid of a code 12?

[hardisk_c]

According to my manual and online, code 12 indicates a battery disconnect within the last 50 cycles. I noticed that this code is still hanging around even though this Jeep is my DD and the last time the battery was disconnected was a little under a year ago. Is that just a default code or does it need to be 50 CLEAN drive cycles. Reason I ask is because there is a code 21 that keeps cropping up when the ambient humidity jumps up and when that happens it feels like the engine might be running on the rich side. This code still hangs around even through 2 O2 sensors, a replacement pigtail, and replacing a dubious wire from the pigtail to the PCM. Could this be stopping the other code from clearing? Could my PCM be going on the fritz? Any help would be appreciated.


oh, btw, working with: '94 Laredo w/ 4.0

[bringselpup]

Are you getting a check engine light or just doing the 3X on off sequence fishing for codes?

[hardisk_c]

I'm getting a very intermittent CEL, and when I pull the codes, the resulting codes are 12, 21 & 55.

[bringselpup]

It sounds to me like that might be what's up. Do you think the frequency of the 21 issue occurs more often than 50 drive cycles to clear the code? If so it really does sound like the PCM never gets to wipe the slate clean and you're still looking at an old 12.

I guess one way to know for sure would be to pick a day that you aren't noticing the engine running a little rich and do 50 cycles and see if it clears.

[hardisk_c]

Hrmph. . . ok. 50 *clean* cycles. Which I guess brings me to part deux. How do I get there? The 21 code seems to come and go at will, mainly when the weather is humid or (like right now) raining. I seem to have inherited it with this problem since purchase, but seems to be getting worse as mileage increases. When it starts to act up, idle won't stay steady, jumps from 700-ish to dropping down to almost 300, back up to 1k, never keeping either for more than a second. CEL light comes on and idle stabilizes @ round 750.

TPS has been tested, IAC, throttle plate, and intake have been cleaned and reassembled with a new gasket along with the items mentioned above. Some things I forgot is that about a year and a half ago, the fuel pump failed on a trip, and the fuel pump and filter are new(-ish now) . Also the CCV valves have been cleaned and the grommets and hoses replaced, but before that it was getting blowby in the air filter. Makes me wonder if the MAP could be fouled with oil and the addition of some barometric (read that humidity) difference could be causing the computer to think the MAP's readings are ok when they actually aren't. Plugs, wires, cap and rotor are all less than a year old.

Right now I'm just asking for ideas; am going to be starting w/ testing the MAP w/ a voltmeter if weather holds this weekend(we're in a wet spell which means the engine will continue to act out) to see if something is funky on the intake side. Any help is appreciated.

[bringselpup]

Maybe wd-40 the snot out of some sensors and connections, just to see if you can find something wet weather is making funky.

[hardisk_c]

Good idea. I'll try to do a follow-up soon as we get rid of the fresh 5 inches of snow we just got (I've already got 1 sick car in a 1-stall garage, not very conducive to working on the DD :P).

Found a Chilton's that I had mis-placed in the process of moving, and I am feeling stupid right now because I just found the "Drivability & Emissions" portion and it looks like a multi-meter is about to become my best friend. . .

[Bob D.]

Have you tried cleaning the battery terminals?

[hardisk_c]

Belated update for those still interested *crickets chirping*

Seems the sensor (MAP) was on its way out. Cleaned it and the harness with some electronics cleaner, and blew out the vacuum line to the manifold w/ some compressed air and reassembled w/ some dielectric grease on applicable parts. . . cue adding codes 13 & 14 and a no-start/flood situation that cropped up 2 1/2 hrs from home and I'm guessing cleaning the (oil-soaked) sensor killed it.

Code 13 - No barametric difference (I'm paraphrasing from what my manual seyz :P)
Code 14 - High or Low voltage detected from the MAP sensor.

1 new MAP sensor and harness later and it even seems like the engine is a bit peppier