Conditions for Setting the DTC

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0621 is not set.
Ignition ON, engine OFF (Prior to Ignition ON, the ignition must have been OFF for at least 5 seconds), the ECM detects a PWM signal that is greater than 65% for 5 seconds.
Engine running at less than 3, 000 RPM - The ECM detects a PWM signal that is less than 5% for 30 seconds.