The P1811 code is one of the most common codes for transmissions in 1997-on GM front wheel drive vehicles. Symptoms of this code include a check engine light illuminated and harsh shifting. Cycling the key on and off may cure the harsh shifting until the criteria for the code is met once more. We are going to cover what causes the code to set and repair options.
Code Criteria
If a shift into any gear other than reverse and forward engagements takes longer than 0.65 seconds to complete, code P1811 will set. The Powertrain Control Module will then command maximum line pressure inside of the transmission, resulting in harsh shifting. The PCM will also command the check engine light or service engine soon light to be illuminated when P1811 is set. Basically, the PCM is sensing a slip, and is increasing line pressure to maximum in order to prevent the transmission from hurting itself further.
Repair Options
In 2002, GM release a technical bulletin for the P1811 code. See the bulletin by clicking this link http://bit.ly/P1811_Bulletin. The bulletin states that a mechanical problem in the Pressure Control (PC) solenoid, contamination in the valve body, or incorrect fluid level can cause the P1811 to set. Those problems could definitely cause a P1811, but what they failed to mention in the bulletin is, what exactly is the PCM looking for when setting P1811. It's looking for a slip of 0.65 seconds or longer to set the code. See http://bit.ly/P1811_Diag_Tree. So it's not as cut and dry as the bulletin makes it to be. A burnt clutch pack, stripped overdrive clutch hub, worn accumulators, worn valving especially the actuator feed limit valve, and just high mileage can all cause this code to rear its ugly head. All of which would require transmission disassembly to repair. Now I'm not saying that P1811 is going to require a major transmission overhaul every time a vehicle comes into the shop with the code. I'm saying that it is not always going to be as simple as just changing out a solenoid.
How to Know if a Solenoid will Repair the Problem
It is impossible to know for sure what the internal shape of a transmission is while the transmission is still in the car. The first thing to check is the transmission fluid. If the fluid level is low, add automatic transmission fluid (ATF) until full. Remember that transmission fluid needs to be checked while the engine is warm and running with the shifter in the Park position. After the fluid level is OK, drive the vehicle to your nearest People's Transmission certified shop to have it checked. If the fluid level was low, there is a leak somewhere that has to be repaired. The shop will then test drive the vehicle while monitoring data on a scanner that is communication with your vehicle's PCM. After that, the shop will most likely recommend a pan drop to see if any contamination is being produced inside of the transmission. If contamination in the form of clutch material or metal is present, then a solenoid replacement will be a waste of money. If the pan is clean, fluid is in decent shape, and the mileage is below 80,000 miles or so, then maybe a solenoid will fix the problem. The thing to remember is, if the shop recommends a solenoid, then they are looking out for your best interests. It still may not fix the problem, but from what they have seen during their checkout, a solenoid replacement is worth the gamble. If the shop recommends a transmission overhaul, ask them what they found that makes them think that is the only option. Don't like what they tell you? Then call The Transmission Guy at Peoples Transmission. 1-888-415-2098
