GMC 2003 hesitates to shift to 4th speed

[Normann]

Hi all,

I'm new to my 2003 GMC Yukon XL 2500 and I'm not fully sure if the tranny works as it should. On flat road, I need to exceed approximately 55 Mph before it decides to shift to 4th gear. I have a 496 (8.1Litre), 4L85E and 3:73 diff. I have changed tranny oil and filter, but that didn't change anything.

Is this what I should expect? Or should the tranny be tuned and is it only possible to tune the tranny with a Tech2?

Sven-Erik

[servantsalesmen]

you're trans is definitely not working correctly. It's probably throwing codes. Have it scanned at a shop with a tech 2.

[Normann]

Should the SES Light be on if the PCM has codes?

If I read the ODB2 port with a normal scanner, it does not have any codes stored, not even a general code from the PCM.

[txab]

The average scanner you're talking Abnout is unable to read the necessary codes

[Normann]

If there are any error codes in the TCM, shouldnt the ECM get a common code (P0700) from the TCM saying that there are trouble codes in the TCM?

[gmtech4]

If there are any error codes in the TCM, shouldnt the ECM get a common code (P0700) from the TCM saying that there are trouble codes in the TCM?

If it has a stand alone TCM like the Allison , he has a pos 4l85 , I doubt he has a TCM

[Normann]

Ok, thanks for the information. Then I guess the PCM might have error codes from the transmission and that these are not triggering the SES light. I will take it to the dealer and have it checked.