I'll even throw in another little "tidbit" to muddy the waters further....
If you are an O/O and only have one truck and trailer, you don't have to complete the DVIR at all.
Quote:
Question 21: Is a DVIR required by a motor carrier operating only one tractor trailer combination?
Guidance: No. One tractor semitrailer/full trailer combination is considered one motor vehicle. However, a carrier operating a single truck tractor and multiple semitrailers, which are not capable of being operated as one combination unit, would be required to prepare DVIRs.
Note this is ONLY the DVIR. You still have to ensure that the vehicle is safe to operate.