Conditions for Setting the DTC
WARNING: This page is about a different car, the 2017 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.
P18C4
Gear position sensor signal 1 duty cycle is less than 10% for 3 s.
P18C5
Gear position sensor signal 1 duty cycle is more than 90% for 3 s.