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Why would I get trouble code 12?

ABN146

NAXJA Forum User
Location
USA
I have never disconnected the battery but I am getting MIL code 12 or battery disconnect.

97 XJ 4.0
 
ABN146 said:
I have never disconnected the battery but I am getting MIL code 12 or battery disconnect.

97 XJ 4.0
It could low voltage. I had that code pop up the other day and I also haven't disconnected the battery lately. It went away after a day and hasn't popped back up yet. I don't have my book handy right now, but a code 12 (IIRC) also has to do with the PCM not getting enough power.
 
Thank you!!! I have noticed that the battery is having problems and seems to be leaking. I have not tested it yet but I think it is on its way out and I guess this could cause a code 12.

I'm very new to these computerized vehicles and problem codes... My other vehicle is an 83 and it is very easy to figure out what is going on with out a computer giving me codes.

Now I've got 3 more codes to figure out

66 11 42

I also got a P0107 or 14, that one is easy to figure out.
 
Why you got the 12 in the first place is hard to know, perhaps a corroded terminal or something, but you should know that once it is set it will persist for the next 50 starts, so seeing it does not necessarily mean the problem continues.

Code 55 is always present. It is the "no-code" that tells you the system is working.

11 is a bad crank position sensor.

66 is not listed in my 95 FSM and I haven't gotten a newer one yet.

42 is Automatic shutdown relay fault.

I would go through things and clean connectors and battery terminals and try resetting the whole system before getting too worried, especially if the engine runs all right. If you get a lot of codes at once it could be something that was triggered by a battery problem while running, rather than the components the codes refer to. Chrysler systems seem to be sensitive to a bad battery, and will often run poorly if the battery is bad enough that it doesn't properly filter the alternator output, which causes overvoltage. It's a common problem if you start a dead one with a boost.
 
After reading Starscream918's post last night I wondered if a battery that is gettting old and not performing well could cause all of my problem codes. I plan to have it checked first before replacing sensors.

Would a battery or connection problem cause my fuel gauge to act up? As I drive it moves from full to empty once in awhile sometimes it stops on half when I know the tank is full.

Thanks for all the help!
 
ABN146 said:
After reading Starscream918's post last night I wondered if a battery that is gettting old and not performing well could cause all of my problem codes. I plan to have it checked first before replacing sensors.
It could be causing the code 12, but I don't think it would cause the others. Since you are replacing it anyway, it never hurts just to see if it really could be.

Would a battery or connection problem cause my fuel gauge to act up? As I drive it moves from full to empty once in awhile sometimes it stops on half when I know the tank is full.
Not that I've ever heard of. That just sounds like a faulty guage or maybe a failing part within the gas tank.
 
Well I checked the battery and it is good but the postive cable is rotten. About 1/4th of the individual wires have broken from the terminal clamp. The 4 inches of exposed wire from the clamp was covered with green corrosion crap. I am guessing this is why I got a code 12.

Better to buy a new cable than have to buy a new battery:)
 
Last edited:
You will ALWAYS get a code 12. It signifies the beginning of the code sequence. And a code 55 signifies the end of the sequence.
 
xjohnnyc said:
You will ALWAYS get a code 12. It signifies the beginning of the code sequence. And a code 55 signifies the end of the sequence.

Sorry, but this is not so, at least for OBDI and OBDII systems that still do the flashing-light codes. 55 is the only code you should get normally. Code 12 is battery disconnect within the last 50 starts. If you have not had a disconnect, you should not get a 12.

If ABN146 had a battery connection bad enough to set code 12 while he was running, all sorts of other signals will be interrupted as well, and it can easily explain the others.
 
Well... I checked on pos battery cables and I was told I would have to go to the dealer for one.
The dealer price is just above $100.00!!!:wow:

I hope to find one at the junk yard.

Anyone know if I have to get a cable from another 97 XJ or can I use cables from other years? If so, what years will work with my 97?

Now I wish the battery was bad:(
 
Matthew Currie said:
Sorry, but this is not so, at least for OBDI and OBDII systems that still do the flashing-light codes. 55 is the only code you should get normally. Code 12 is battery disconnect within the last 50 starts. If you have not had a disconnect, you should not get a 12.

If ABN146 had a battery connection bad enough to set code 12 while he was running, all sorts of other signals will be interrupted as well, and it can easily explain the others.

OK, I should have said that I always get a code 12 at the beginning of the sequence, even though I hadn't disconnected the battery.

And I have read on someone's site that this is sometimes the case.. But for the life of me, I can't find that site now. :)
 
xjohnnyc said:
OK, I should have said that I always get a code 12 at the beginning of the sequence, even though I hadn't disconnected the battery.

And I have read on someone's site that this is sometimes the case.. But for the life of me, I can't find that site now. :)

My 95 and my daughter's 93 do not give a 12 normally. As far as I can see from the 95 FSM, if you're getting that code there's a problem somewhere, and if the battery has not been disconnected, then your PCM is losing standby power when it shouldn't. That is, unless they changed the codes at some point. But I don't see why they would have, since there is no point in adding a second code to indicate a no-code condition. A single no-code (55) is all that's needed.
 
xjohnnyc said:
OK, I should have said that I always get a code 12 at the beginning of the sequence, even though I hadn't disconnected the battery.

And I have read on someone's site that this is sometimes the case.. But for the life of me, I can't find that site now. :)
My 97 has shown a 12 and 55 since the day I got it. Using the key cycling method or using a snap on scanner. I consider it to be the "beginning" and "end", but never bothered to check any farther.
 
JohnX said:
My 97 has shown a 12 and 55 since the day I got it. Using the key cycling method or using a snap on scanner. I consider it to be the "beginning" and "end", but never bothered to check any farther.

It wouldn't surprise me if they changed it in 97 or even 96 when it was a hybrid of OBD I and II. My 99 doesn't return any codes at all with an OBDII scanner, and neither does my son's 96 as far as I can remember.
 
JohnX said:
My 97 has shown a 12 and 55 since the day I got it. Using the key cycling method or using a snap on scanner. I consider it to be the "beginning" and "end", but never bothered to check any farther.

Thanks John. I knew I wasn't nuts. But it's sometimes hard to convince others of that. :)
 
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