Error codes U016400 and P068A00?

It sounds like the Main PCM relay needs to be replaced.

The error codes U0164 and P068A that you're referencing relate to communication and power management issues within your vehicle. Here's a breakdown of these codes:

U0164: This code is typically defined as "Lost Communication with HVAC Control Module." This means that the main computer of your vehicle (usually the Engine Control Module, ECM, or Powertrain Control Module, PCM) is not receiving a signal from the HVAC (Heating, Ventilation, and Air Conditioning) control module. This could be due to a fault in the control module itself, the wiring between the ECM/PCM and the control module, or even the ECM/PCM itself.

P068A: This code means "ECM/PCM Power Relay De-Energized Performance - Too Early." This indicates that the ECM/PCM has detected that the main relay was de-energized too early. This often refers to an issue with your vehicle's main computer not maintaining power as expected. It could be due to a faulty relay, an issue with the power/ground circuit, or the ECM/PCM itself. In some cases, this might be related to a weak battery or an alternation not providing adequate charging.

Please let us know what happens.