Code P1811 is hands down the most common trouble code and commonly asked about problem. This code can set for numorous reasons and often by a failing pressure control, BUT on higher mileage transmissions this is often not the case or at least is not the only cause to the problem. With that said it is important to understand that replacing the pressure control solenoid is NOT a guaranteed fix!
This code will set when the pcm/tcm detects excessively long shift times. For every shift the pcm/tcm watches how long the shift takes to complete in milliseconds. If the shift times are over roughly the 0.6 second timeframe and the pcm/tcm tries to compensate for this by raising line pressure and still does not see acceptable shift times after a few shift cycle it will trigger code P1811. When this happens it puts the transmission in a max line pressure condition to help protect the transmission against excessive slippage and burnt clutches. While this condition is present you will feel harsh shifts, some vehicles more agressive than others, and you will also hear a whine noise similar to what a power steering pump that is low on fluid will sound like. You can shut the engine off for a brief moment and restart the vehicle and it will feel normal again until a few shift cycles of excessive shift times and the cycle will repeat itself. This typically only happens after you have driven for a short while and the transmission and its fluid warms up.
Some common causes to this problem are-
-Poor working PCS (Pressure Control Solenoid), also called EPC or Force Motor
-Excessive clutch clearances
-Poor functioning accumulator system
-Worn internal seals and sealing rings
-Excessive valve body wear
-Dirty MAF sensor resulting in lower commanded line pressure
Due to the list of potential problems it is difficult to suggest just one or two items to cure code P1811 as everything above and many other parts and variables all play a role in the effect. Unfortunately because of the orientation of this transmission and how it sits in a vehicle it requires quite a bit of labor to access the pressure control solenoid as well as the valve body. One thing popular to try before diving into an expensive and labor enduring repair is to install a shift improver kit such as the Transgo SK4T65E shift kit that we offer. This kit includes a new set of accumulator springs and spacers to limit accumulator piston travel which greatly speeds up the time it takes to apply a clutch, which hand in hand will shorten the shift time. These kits are not made to create firm or harsh feeling shifts but to help speed up shift timing and keep what the pcm/tcm wants to see in check to prevent code P1811 from triggering. As mentioned above higher mileage plays a big role in how this transmission works and also means you should replace parts with caution and have the understanding that there is no 100% guaranteed fix to this problem without tearing into the entire transmission to address and upgrade the problem areas.