Pressure regulator is hanging up, common issue. Flush & fill with the correct ATF

 

Is the Pressure regulator the same as the pressure control solenoid? I was told by many not to flush the transmission fluid since it has never been changed. Just change the filter and re-use the old transmission fluid. Any thoughts?

 

Yes it's also the control solenoid and what happens is the PCM actually measures the shift overlap time and if it's not to spec it will ramp the pressure to full as a protection system. I had issues with the shift patterns and did a flush & fill with 200k on the clock using the correct Dexron VI. To just replace the filter and dump the old oil back in makes absolutely no sense, seriously? I have to really question this advice and the person giving it.

My fluid change consisted of dumping the old oil & filter without starting the engine, the torque converter will leak down to the 1/2 way point in about 24 hrs. I then dropped in the first gallon of Dex-VI, started the motor then topped it up over a 10 minute period. Warm and full I put on a few hundred miles of mixed highway and in town driving then sucked the oil out with a vacuum pump thru the dipstick pipe and refilled with fresh Dex-VI again. This was to dilute and circulate out the trapped oil in the valve body and servos, a lot of work but not a problem since. Shifts are good and the converter apply is much better, positive but not harsh.
I had very little crap in the trans pan or filter, no broken metal parts or shavings on the magnet despite the 200k miles so I suspect it may have been replaced at some point.

There are cases of post flush failure with these, I don't know the reasons why but it's a proven procedure with a good track record. Just make sure the correct Dex-VI is used, Dex-III was discontinued in 2011 and GM supports only Dex-VI for the older transmissions. (https://en.m.wikipedia.org/wiki/DEXRON) This is a good article about the history of the fluid.

 

It is absolutely the pressure control solenoid. It's not hard to change, but it does require work and experience... I just fixed this last week. Took me 4 hours. There are several guides on how to take the side cover off the transmission. The part is about $40 online. 7 quarts of dexron 6, and a filter is $12. Both gaskets are reusable, as long as they're not damaged.
Don't use the same/old fluid unless you KNOW this transmission has never been serviced and actually slips from wear. Don't flush it either. Just drain it, change the filter, then the PCS, put it back together, put about 4 quarts in and start it. Slowly add fluid until it's full. Check the level again after a few drive cycles. Even with no check engine light, you'll have code P1811 (max adapt/long shift).

 

This is a very common problem on the 4T65E. After thousands of miles things will wearthy down and break. These transmissions are a weak point on this platform. A fluid/filter change without a flush is your best defense against more harsh shifting and or slipping. NEVER ever flush these because it can accelerate the already worn parts like the clutch packs, bands etc etc. That P1811 DTC is also common as it's due to the transmission control module going into a "safety" mode thus causing it to increase line pressures to "MAX" and the prolonged shifts will be harsh due to that. You can also tell by hearing a buzzing/whining sound coming from the left front area of the car by the wheel. There will be no CEL for this problem as its on the TCM to detect a fault in the transmission and when the transmission is cold you will have "soft" shifts for up to 20 minutes of driving until the fluid is warmed up. The long shifting is due to the PCM seeing a longer than 0.065 seconds shift time and it will default line pressure to "max adapt" to avoid driveline damage to the transmission and you will also see much harder shifts than normal. The temporary fix is to shut the car off for approximately 1-2 minutes. After that the car will shift normal until the PCM detects longer than normal shifts thus throwing it in that safety mode again. The best fix to this problem is to change out the pressure control solenoid and that may fix the issue entirely. If that is not the case a rebuild could fix that as well as other transmission-related issues. Hope this info was helpful!