Tri-City Diagnosis: We could not duplicate the customer’s concern on road test, since it is intermittent. However, there was a diagnostic trouble code P1811 stored in the computer, the definition of which is maximum adapt & long shift. This particular code matches with the customer’s described symptoms… a hard shift one day and normal the next. We installed a pressure gauge on the transmission and compared it to reading from the computer data stream on road test. This information concluded a bad electronic pressure control solenoid (aka EPC solenoid) as the cause of the problem.
Tri-City Recommendation and Final Resolution: Remove transmission pan, inspect transmission filter to verify the condition of the transmission. If transmission is sound, then replace the EPC solenoid, update the valve body, replace transmission filter and service the transmission. Total cost: $850.00 .
Tri-City Transmission of Tempe Comments: This is a repair that we consistently perform at least once a month. Customers are frustrated because most of the time the vehicle drives just fine. They don’t believe the first repair shop they go to that tells them they need a new transmission, and they are right not to. Most shops will be quick to either overhaul or replace this transmission for this code. They simply don’t have the knowledge or experience to accurately diagnose the problem and only fix what is necessary. General repair shops performing transmission work are typically the first to make these mistakes.
Why does this happen intermittently? When the circumstances are right, the computer picks up a slight slip of the transmission. The driver will not necessarily notice this but the computer is more sensitive to the slippage than the driver. In turn, this sets the P1811 code – because the computer knows there is a slip, it will electrically open and intensify the pressure in the transmission in order to compensate for the slip. This is when the driver feels the hard shifting or as it’s sometimes described, jumping or bucking. The thought sets in, oh no; I have a transmission problem. However, when they get in the car first thing the next morning, the problem has seemingly resolved itself, and it may not happen again for another week, month, or even months. So it mostly goes ignored and untreated. The P1811 code, while stored in the computer, is not active in the running programming until the conditions are right.
This problem can be fixed as described above, if it has not been neglected to long. Getting it fixed sooner rather than later is imperative to avoid an overhaul or replacement the of the transmission.
There are technical service bulletins from the General Motors (GM) specifically referring to this problem. This transmission problem is found in many front wheel drive GM products such as: the 2001 – 2005 GM Passenger Cars with 4T65E Automatic Transmission (A/T). Some people refer to this transmission as the 4T65E, 4T65, 4T60E, 4T60, TH440-T4. This would apply to Buick Rendezvous, Buick Terraza, Chevrolet Venture, Chevrolet Uplander, Oldsmobile Silhouette, Pontiac Aztek, Pontiac Montana & Saturn Relay.
