TRANSMISSION ISSUES HERE WE ARE AGAIN STILL SAME ISSUES AFTER CHANGING ALL 5 SOLENOIDS,FLUID,FILTER AND EVEN THE INTERNAL WIRING HARNESS IN 4L60 TRANSMISSION IN A 97 YUKON. STILL GETTING A P0785 CODE. WHEN 1ST STARTED SHIFT PERFECT TILL IT WARMED UP AND I MAKE A COMPLETE STOP. THEN IT WON'T DOWN SHIFT AT ALL AND I HAVE NO OVERDRIVE. HAVE NEVER HAD ANY PROBLEMS WITH TRANS TILL IT STARTED DOING THIS OUT OF THE BLUE. NO SLIPPAGE NO BURNT FLUID EITHER. I'M TOTALLY LOST AND DON'T WHAT ELSE TO DO. CAN ANYONE PLEASE POINT ME IN THE RIGHT DIRECTION? PLEASE EMAIL [email protected]

Here are some possible causes and steps to consider:

Check the transmission fluid level and condition. Shifting issues might be caused by low or filthy transmission fluid. Check that the transmission fluid is at the proper level and seems clean and red. If it is low or polluted, a fluid change and filter replacement may be required.

Transmission Solenoids: Modern automatic transmissions employ solenoids to manage gear shifting. A faulty solenoid might cause the transmission to stay in one gear. If needed, a professional can diagnose and replace malfunctioning solenoids.

Transmission Control Module (TCM): The TCM is in charge of controlling the operation of the transmission. It can cause shifting problems if it malfunctions or receives inaccurate sensor data. Check the TCM for fault codes and functionality.

Wiring and Electrical Issues: Examine the transmission's wiring and electrical connections, especially those to the TCM and sensors. Damaged wires, faulty couplings, or electrical issues can all disrupt transmission operation.
Shifting problems can also be caused by internal mechanical faults within the transmission, such as worn clutches, damaged gears, or a malfunctioning valve body. These problems can be diagnosed and repaired by a competent transmission mechanic.

Transmission Fluid Pressure: Proper gear engagement is dependent on transmission fluid pressure. Shifting might be affected by a malfunction with the transmission pump or pressure regulator. A pressure test can aid in the diagnosis of these problems.

Examine your vehicle for Diagnostic Trouble Codes (DTCs): Even if the knock sensor problem has been rectified, there may be more DTCs associated with the transmission problem. Check for any stored trouble codes with a diagnostic scanner to gain more insight into the problem.

I hope this might be helpful.

Could be. Have the codes read. Could be the engine sensors, transmission sensor/solenoids wiring harness internal and external, Or the transmission clutches are worn out.

Could be the TCC solenoid stuck. It is part of the internal wiring harness for the transmission. It will keep the transmission in overdrive. Thus killing the engine. Pull the pan and check for metal floating in the fluid. No metal. Change the 1st and 2nd shift solenoids, EPC solenoid and internal harness.. If there is metal flake. I would pull the valve body and make sure it is clean. Use a pick to make sure the piston move freely. Clean them one at a time. Easy to tear down. Watch the clips, they tend to fly off.

In general you drain the transmission fluid from the pan, drop the transmission pan and filter, then the solenoids are readily visible and accessible. Disconnect the wiring harness on the solenoid and the fastener/lock on the solenoid and remove it. Worst case you may have to disconnect the solenoid wiring harness and drop the valve body. I've found audiworld a great source of information. Get a Bentley manual for your car.

HERE WE ARE AGAIN STILL SAME ISSUES AFTER CHANGING ALL 5 SOLENOIDS,FLUID,FILTER AND EVEN THE INTERNAL WIRING HARNESS IN 4L60 TRANSMISSION IN A 97 YUKON. STILL GETTING A P0785 CODE. WHEN 1ST STARTED SHIFT PERFECT TILL IT WARMED UP AND I MAKE A COMPLETE STOP. THEN IT WON'T DOWN SHIFT AT ALL AND I HAVE NO OVERDRIVE. HAVE NEVER HAD ANY PROBLEMS WITH TRANS TILL IT STARTED DOING THIS OUT OF THE BLUE. NO SLIPPAGE NO BURNT FLUID EITHER. I'M TOTALLY LOST AND DON'T WHAT ELSE TO DO. CAN ANYONE PLEASE POINT ME IN THE RIGHT DIRECTION? PLEASE EMAIL [email protected]

Hi, you can download a manual here, but it does not specify the transmission capacity:
http://www.extendedgmwarranty.com/owners-manual/chevrolet/2006-Chevrolet-Express.pdfHere is the info you need:
4L60-E transmission Service change only - 5 quarts. Total refill - 11.2 quarts.

Total refill would include a tear-down of the transmission and empty the torque converter. If you are just dropping the pan and changing the filter, 5 quarts should do it.

when changing the filter? maybe 4, at overhaul maybe 10-11?

Most transmission solenoids are located within the pan. If you replace the solenoids then it would be a good idea to change out the wiring harness that runs from the main transmission plug to the solenoids. Just lower the pan and drain it. Then, remove the one or two bolts that hold the solenoids in place. Replace the solenoids, wires, transmission filter and fluid at the same time (since you're already there). Make sure that you use a new pan gasket when you put the pan back on or it will leak fluid. Good Luck!

If the unit worked before you parked it, likely you had a varnish buildup inside that was the result of lack of service or an overheat condition previous to parking it.(while sitting the varnish can harden up and cause internal solenoids and valves to become stuck) The only real way to remove the varnish would be to remove it and have it rebuilt. You could try something like changing the fluid and using an additive such as the one made by Lucas. I would also check any electrical harness plugs going to the transmission to make sure none have become corroded, as that too can affect the shift pattern, If changing the fluid works, change it again in 2,000 miles to remove anything that could block the filter.