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There is no vacuum modulator valve , this transmission is all electrical controlled . What seams to be the problem ? no shifting , shifting hard ETC....... shift solenoid inside the transmission maybe , input or out put speed sensor bad . Do you have a check engine light lit ? There probably is a DTC - diagnostic trouble code .
You may have transmission troubles. Is the fluid up where it should be? I did have trouble with shifting and my mechanic drained the fluid all out and changed the filter that's in the transmission.
I did a car myself but found it was very dirty as you have to take the transmission pan off There is no drain hole like the motor. mine had about 12 bolts that holds the pan in place as well you need to make sure the gasket is installed properly.
-Check the shift linkage cable to the shift arm at the transmission.
Is it still connect good? If so, check transmission fluid. (Must be full to indicator level when it's hot while the engine is still running.)
Automatic transmission can't run without fluid.
Before guessing at transmission problems, check the fluid level (car warmed up, engine running in Park on level ground) and have the PCM scanned for trouble codes FIRST. 1-2 / 2-3 shift is delayed and harsh, may not shift into OD: Check TPS for smooth and linear electrical response over the entire range of motion. If not, replace. Start with that and here is a link for obtaining your DTC codes to your Sonoma. http://www.troublecodes.net/GM/ Thank you for using fixy and good luck
If the transmission oil is full and the clutch master cylinder is full, feels normal and does not slip going up steep grades, likely the gears in the transmission are worn (usually synchros). All items above contribute to proper shift engagement.
Hi. the first issue may be a clogged filter on the transmission. i would check the filter to see if its dirty or needs to be changed. The next problem that may be causing the shift issues could be the speed shift solenoids. if these devices are malfunctioning, they can cause the transmission to not shift correctly. i suspect a bad or dead shift solenoid. they are located inside of the transmission pan. If you pull the transmission pan and you see a lot of dirt and metal pieces on the bottom of the pan, you may need to rebuild this transmission soon.