Conditions for Running the DTC

WARNING: This page is about a different car, the 2002 GMC Safari and 2002 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.

The battery voltage must be between 9 and 16 volts.
Ignition switch in the RUN position.
The park lamp switch, which is part of the headlamp and panel dimmer switch, must be in the OFF or AUTO position and the ambient light sensor must be in the DARK state.
The park brake released.