DTC P1633: Ignition 0 Circuit Performance: Description

WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) receives the following ignition inputs from the ignition switch:

Ignition 0 signal.
Ignition 1 signal.
Crank signal

The PCM uses a Class II Ignition mode message and the voltage input from 2 separate systems to test the ignition 0 circuit. If PCM detects an improper ignition 0 signal, DTC P1633 will set.