Usually I get cars towed in on a flat bed...but this tow truck showed up EMPTY! Why?

Customer said that after a recent "Exhaust System Upgrade", the PTO system became very unhappy: it engages and then shuts off after 20 SECONDS...He can't use the flat bed without pressing the PTO button every 20 seconds!! Not good...

The code set is a P1123PTO System Performance.

Let's do some research and figure out WHY is this code setting.
The diagnosis is complicated by incomplete information on the "Upfitter Equipment"...
Which Module is unhappy...ECM? TCM? VSIM?

Will we be able to get the PTO system functioning with NO PARTS REQUIRED?

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Ivan