2008 Chevy Uplander not locking

Looking at the service info for your Uplander, it has Remote Control Door Lock Receiver technology, so keyless entry should work if you have a capable key fob.

Your Uplander will need the key fob programmed by a service center or dealer with the technology to program those GM vehicles that can't be done manually (i.e. Tech 2 scan tool).

Try pressing the unlock button twice

Keyless Entry
The keyless entry system consists of the following:

• smart entry control(SEC)/timer module
• keyless entry remote transmitters
• power door lock actuators
• body side door power door lock actuator
• liftgate actuator
• power door lock switches
• door ajar switches
• Principles of Operation
  All doors can be locked at once by turning the door key lock switch to the locked position. An individual door can be unlocked by moving the door key lock switch to the unlocked position and turning it again within five seconds; all the doors (including the liftgate) will unlock.
  The smart lock system is designed to keep the driver from locking his keys in the car. It will lock and then unlock all the doors if the smart entry control(SEC)/timer module detects the following conditions:
  
  • The ignition key still in the ignition.
  • A front door is open.
  • A door lock switch has been pushed to the lock position.
  The panic feature has a duration of 30 seconds from the last time the PANIC button is pressed. When locking the doors from the remote transmitter, the horn chirp/lamp flash feature can be disabled or enabled by holding the LOCK and UNLOCK buttons for two seconds. The hazards will flash three times to confirm that the feature has be enabled or disabled.

The control module probably see's an input that shouldn't be there . lock Switch , door ajar etc... Don't think it has anything to do with the remote . Some part stores have a tester to see if signal from the remote is working . Or the dealer ! Take it an see if your remote is sending a signal without you pressing any buttons .
If it is you need a new one .

The problem is with the remote key FOB then. Replace it.

there should be a relay and a fuse for the locks and the windows

There are no keyless entry remote self-programming instructions for the 2008 Chevy Uplander. You must get an Automotive Locksmith to program the remote to your vehicle for you.

It could be the power lock motor. You could have a short or bad wiring harness. Might just be a fuse that connects to both. But since you said it's only the driver side. When the power lock motor is bad it can trigger your alarm because they're wired together.

Hope that helps. Good luck.

You must take it to the Chevy dealer.

I have a 2006 Chevy Uplander and I also drive a 2008 Chevy HHR for my company vehicle. this may not be your problem but in my personal vehicle and also our company fleet vehicles i have experiened Key fob failures. the first symptom was that the fob would stop working intermittently, then stop working all together. if you open it you may see that the clip that holds the battery and makes the circuit connection has come un-soldered from the board. if you are careful you can re-solder this and you are back in business. be careful not to damage the case. if it shows signs of opening, the dealer will not troubleshoot your problem and they will make you purchase a new fob.