Chrysler Repair: 92 grand caravan:bus failure, bias level, drb ii

Question
QUESTION: lost all my dash guages then befor i got home tranny went in first gear and will not shift up fluid is full and not burnt had codes read said  bus failure . enging is running fine it is a 3.3 had the dash checked out no shorts or opens even changed body module and relays no differance checked dash with a good known dask no differance any ideas all fuses and links are good did replace engine 6 months ago broke cam  van has 160,00 k,s on it  also new alternator and starter

ANSWER: Hi Peter,
The bus failure could be due to a variety of specific causes which can best be differentiated by use of a Chrysler Diagnostic Readout Box II (DRB II). Is there a chance you can find some shop with that tool? If not, I have one, but I'm in California.
The trans symptom is synonymous with a bus failure of some type, too. The DRB will tell you which of these reasons is the cause: short to battery, short to 5 volts, short to ground, bus + and bus - shorted together, no termination, bus bias level too low, bus bias level too high, no bus bias, bus + open, bus - open, bus+ and bus - open, not receiving bus messages correctly. Then I have the fault tree type manual that shows how to correct whichever one of these specific faults is displayed.
So let me know what resources you have there. The bus wires are a twisted pair so that would help in tracing them. The wires connect between the powertrain module, transmission module, instrument cluster, air bag module, overhead module (if equipped), and body computer. So somewhere in that data network we have an issue that needs to be found and corrected.
Roland

---------- FOLLOW-UP ----------

QUESTION: are they colour coded or just twisted  I have a otc scope but due to a injury i receaved in kuwait in 91 i have some trouble with recall.

Answer
Hi Peter,
The colors are white/black (-) and violet/brown (+). The blue plug at the body computer should have 12V on pin 12 when the ignition is in the run position, pin 13 should be grounded, and pin 14 and 15 should each have 2.5V bias, + and -, respectively, which are the twisted pair. You should find that bias voltage at all the modules I described previously on the same color twisted pairs. If not, you could try pulling all the plugs and determining if the body computer is putting out that bias voltage, then check whether the 14 & 15 pins of the blue connector seem to be grounded by accident so as to check the distributed wiring harness for faults, and also check for opens. Let me know what you find, if anything, interesting.

Roland