I have a 00 3500 5spd that has been driving me crazy! The truck has OEM program with 4" exhaust & open air intake. The tach will stop working @ 2500 rpm and fall to 0, chk eng light comes on & retards power if I slow the eng down the tach will start working again & the power comes back. It has been @ Cummins, Dodge, & several independant shops & noone can find the issue. Cummins spent hours on the phone with Cummins North America & they don't have an answer & noone has ever heard of this problem. Now the laundry list of replaced parts, Inj pump, Lift pump, Crankshaft position sensor (7 times), Engine position sensor, Dodge PCM, Cummins ECM, Wiring harness has tested good, Batteries, Throttle position sensor. Dash cluster has been tested good. HELP!!!!!!!
Also current Fault codes are 1682, 1687, 1693, 1694

 

It really sounds like you have a wiring issue. All of these codes relate to loosing "bus" messages... The bus is the wire that each computer uses to talk to the other computers...

 

Well, this isn't very promising. I'm having a similar problem, however only getting the CEL P1693.
The same exact issue, the tach will drop to 0, truck will run like total crap, and once the tach. starts working again all the issues go away. This truck was really hacked up by whoever owned it before, so it wouldn't surprise me at all if it were an electrical problem.