2002 Trailblazer check engine light--Cruise Control

has a fuse and an actuator motor or
the set resume switch could be faulty

code p0320 refers to cam shaft position (CKP) sensor/engine speed (RPM) sensor--circuit malfunction=== causes --wiring--CKP/RPM sensor ---ECM
because the engine runs ok until it is on cruise control I would be investigating the RPM sensor for a fault
The cruise control takes its control from the RPM sensor and if that circuit is interminable the the cruise control doesn't know what rpms to maintain.

hmm seems like the connection from the cruise control box to the throttle body needs to be checked if its controlled electronicly have the system serviced

There's a recall for the cruise control deactivation switch. This could be your problem. Contact yo

check cruise control fuse and check the brake lights see if brake light working because the brake light switch will deactivate cruise control when brakes is applied.if brake lights dont work either fuse blowed or switch bad.if all is good have vechicle code scan because cruise control control by PCM and vechicle speed sensor and thottle actuator control motor.

I would check the turn signal switch. The cruise and turn signal are on the same switch. The brake lights go through the switch before going to the brake lights. And the turn signals don't work with the ignition off.

The cruise control can be disabled for several reasons, one is if the check engine light is on or if the speed sensor is inoperative.

Normally when this happens, your computer has a stored or active check engine light code. If there is a code present, your computer will disable the cruise control feature until the check engine light or code is cleared.

for parking brake and abs check for parking brake switch operation, for abs check with scan tool for any trouble code, for your cruise control unit check for any broken vacumm hoses on the engine, for the ac fan, check the fan motor, relay or fuse.

possably a vacuum leak. the check engine light comes on with an emmissions issue, ie vac leak, and it will not allow the cruise to work. once the error is fixed, your cruise should work properly again