Re: Strange electrical problem

From: David Gersic (info@zaccaria-pinball.com)
Date: Sat Apr 11 2009 - 12:24:19 EDT


On Sunday 05 April 2009 10:12 am, David Gersic wrote:
> Further digging and research on this one. I found the problem with my 4WD
> not working. The Transfer Case Control Module (TCCM) is dead.

4WD works again. I picked up a TCCM (the "G" suffix version) from an '03
Durango in a junkyard in Joliet yesterday, right next to the famous Joliet
state prison ("Blues Brothers"). Plugged in the power connector, tested it
with my meter, and confirmed 5V on the A8 and B8 output pins. Installed it
last night, and the transfer case now works fine again. So *that's* fixed.

I'm still researching the CTM. I found an '01 base model Dakota in a junkyard
in Lockport and snagged the CTM out of it.

And I learned something new. The PCM talks to the TCCM over the PCI bus. The
PCM also talks to the CTM and the instrument cluster. The FSM (warning,
acronym overload!) says that on 2WD vehicles that the "Service 4WD" light on
the instrument cluster is "electronically disabled". I had noticed in testing
the TCCM that my "Service 4WD" light wasn't working, but had figured that it
was just a bad bulb or something. It wasn't.

The "service 4wd" light is supposed to come on during the dash lamps test at
startup, if the TCCM detects a fault, or if the PCM doesn't receive
communications over the PCI bus from the TCCM. In testing the TCCM, I had
disconnected the battery and removed the TCCM, then reconnected the battery.
That is when the "service 4wd" light stopped working.

When I connected the replacement TCCM to power, that also connected it to the
PCI bus (same connector). The PCM noticed this, and when I then removed the
TCCM for the drive home, the PCM noticed that it wasn't getting messages from
the TCCM any more and turned on the "service 4wd" lamp to complain about it.

Having now reinstalled the TCCM, the "service 4wd" lamp is again being
illuminated at engine startup along with the rest of the dash lamps.



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