So I’ve had a tac 20 go out on me every 2- 3 weeks. It shows viscosity on the car status but is not running the pump. There is an 1155 fault logged which is not in the book for tac 20s but it gives a short description of INIT SD MCE/MCD in remote fast. Will not start working with a reset or pulling the hook but will start working if you put it on inspection and then back to auto. On the 1155 fault the Dvel is showing 149 fpm while the Cvel is showing 0. Hours after the 1155 is logged it has a 1042, and 1103. Car status shows viscosity and group shows normal. Aribiter shows

motion 20: viscosity
Calls 20: viscosity
F door. 20: viscosity
R door. 20: viscosity
Speed. 0: automatic
Lockouts 0: automatic

Automatic 2: no calls
Viscosity. 3: shutdown

It’s alway found in the basement
Any insight would be appreciated

So this is kind of confusing but what the car means to say is that it’s on “Viscosity Overtemp Shutdown” not heat up the oil “Viscosity.” I think it was a certain version of software that started showing an overtemp like this. Usually this is either an overtemp (OLTO) input or the starter has faulted (MCF) input.
I have no idea what an 1155 fault is though.

1155 fault is MCD active and MCE active after MCC outputs fire:possible failures: (1) old generic software, resolution: update generic software to v4r5p, where possible. (2) loose connection in MCD circuit, resolution: check all wiring. (3) Bad input, resolution: replace IOA for tac20-03 or 188e tac22/tac20 (4) up run stall timer, Z35, set to low, resolution: increase Z35 adjustment.

If this helps, it's the info I had.on your fault at least.

I’m putting all new relays in for the valve and replacing the logic board on the soft start because I was able to get it into the same viscosity status by injecting MCE or MCD when it shouldn’t be on, it won’t produce an 1155 but I figured it’s somewhere to start.

I’m going to try updating the software too, I believe I have that latest version

I had the same problem on a tac-20 and the solution was to adjust the oil thermostat underneath the tank.