Weird, weird lights

[Belchos]

2004 California. Original batteries. 80K miles.

Yesterday truck sat out in RAIN (5 inches in 24 hours! All time record for this date here).

I was working on my VW and heard the hazard lights clicking on my Dodge. I started fooling with it and the hazard lights went out, but the headlights were on with the headlight switch off and the key on START. The instrument panel was completely dark. Everything else on the truck worked normally. If I turned the key off, the lights went out. When I switch the key to on, the lights come on about one second after I turn the key/switch.

On two occasions that were not unique in any way that I could determine, the instrument panel went on and the door ajar chime was activated. I hit the code in the odometer and it gave a code of J1652 (Communication Bus). Then the panel went out again and the lights came on. Dimmer doesn't change to high beam. Signal lights don't work.

When you disconnect a battery, is it just one battery, or both?

Does anyone know where the "Communication Bus" is?

Help!

__________________

 

[rbattelle]

The batteries are in parallel. In other words, the system still has power with one battery disconnected.

The symptoms you describe immediately made me think of a bad TIPM, but there was no TIPM until 2005, so that can't be it.

The next logical place to look is the Front Control Module (FCM). This is located directly beneath the integrated power module (the fuse block). It's not uncommon for this to go bad on pre-2005 trucks, and when it does it has many very strange symptoms.

The computer actually gave you code J1652? I can find no record of such a code in any of my documentation. Are you sure you read it right?

-Ryan

 

[Belchos]

Final, final

All problems slowly disappeared over two-day period, so it was probably the moisture.

I got the code result for 1652 from an old post of 2003 codes as, "COMMUNICATION BUS. " Is that a name/description/term for the component you mentioned?

New questions arise if it was the moisture:

What got wet?

How did it get wet?

If I can't figure out the first two, will it happen again, and how can I protect against it?

 

[Belchos]

More on code

The P1652 code apparently refers to the PCI (Programmable Communications Interface) which is the J1850 multiplex system that communicates from the FCM. I've never seen it. I think most or all of this is hidden by the "fuse box" (IPM), but I am going to take a look, to see if the moisture mystery may be solved.

 

[rbattelle]

Ah ha! P1652 - way different from J1652.

I suspect you're right, and the moisture caused an issue. The Front Control Module remains my top suspect. It's located directly beneath the fuseblock.

-Ryan

 

[WhiteSheep]

How is your battery voltage? With 6 year old batteries I would highly suspect them.

 

[AH64ID]

If you had a moisture issue from rain (albiet a LOT of rain) I think you should reseal your connections. Try to get some dielectric around the mating surface of the plugs, and make sure they are all tight. It was probably one of the big plugs under hood, or under the fuse box.