Hi

My engine light came on and it wont shift into final gear can't get a code off the engine with my scanguage rpms and everything else seems to be ok oil and transmission fluid are at the right levels.

Cheers

How many miles on the vehicle? When did you last change the transmission fluid? Are you close to an Autozone? They will scan for free. If their scanner does not pick up anything, you may have to take the car to a transmission shop, or someplace that can scan for chassis and transmission codes.

It is difficult to determine the problem without more information.

it has 74k on it the throttle position sensor was replaced on a recall in feb. the alternator was replaced last October. There are no aftermarket addons to the car.

Have you ever changed the transmission fluid/filter?

they were checked last oil change 4k ago

4000 miles is a long time and many things can happen during that time. Please verify that your trans oil is at the correct level.

And I don't understand how a scan gauge can't retrieve codes from a 2008 GM. ???

Friend of mine had a different code reader and I got 3 codes
U0100 Lost Communication With ECM/PCM "A"
U0101 Lost Communication with TCM
U0073 Control Module Communication Bus Off

so looks like I fried a computer maybe found out the first code puts it into limp mode so that should explain the not shifting guess I might ned a new computer unless it was moisture or a loose connection

Hmmm, I wouldn't go that far. If a computer is fried, well, its fried. No start, no bells, whistles, dongs, dings, no shifting etc.

Let'* try this...disconnect the POSITIVE side battery cable, and short it to the GROUND terminal on the battery. Go check your mailbox, come back, reconnect the POSITIVE cable back to the battery. Restart the car, go for a drive. See if you can duplicate the same thing again.

those are like network errors on a computer and going by the third there is a controller for the bus or cars network i would guess that would be the issue, those others would be byproducts of loss of comm.

nevermind

U0073 - Control Module Communication Bus A Off

Description: This DTC is set when the controller area network (CAN) between the powertrain control module (PCM) and data link connector (DLC) is open.

Possible Causes: • Communication error

Diagnostic Aids: Network DTC concerns occur during module-to-module communication. For additional description and operation of the vehicle communication network, refer to the Workshop Manual Section 418-00, Module Communications Network.