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Error Code P1811 is defined as Maximum Adaptive & Long Term Shift.
This error code is a manufacturer-specific trouble code, meaning it does not apply to all vehicles makes. Rather, it applies only to specific vehicle makes, such as Buick, Chevrolet, GM, Pontiac, etc. Specification of the definition, troubleshooting, and repairs still vary from one make and model to another.
As the engine run with the adaptable shit occurred, the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) identifies throughout the following conditions happened twice per trip: Condition 1: 1-2 Shift over 0.65 seconds, and 1-2 Shift adaptive reaches its limit. Case 2: 2-3 Shift over 0.65 seconds and 2-3 Shift adaptive reaches its limit. Case 3: 3-4 Shift over 0.65 seconds and 3-4 Shift adaptive reaches its limit.
If the shift from one gear into another other than reverse and forward engagement takes more than 0.65 seconds to complete, then the Error Code P1811 will be set. The PCM will command the maximum line pressure inside the transmission, which results in harsh shifting. The PCM will also activate the Check Engine light and set the code simultaneously.
In many cases, the PCM will sense a slip and will increase the line pressure to maximum to prevent the transmission from further damage.
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other symptoms include:
- Harsh shifting
- Harsh upshift or garage shifts
- Erratic shifts
Cycling the key on and off may remedy the harsh shifting until the criteria for the code is met at once.
Many problems result in the activations of this code, namely:
- Defective Pressure Control Solenoid (PCS), this is also called EPC or Force Motor in other makes
- Open or shorted PCS harness
- Poor electrical connection in PCS circuit
- Low transmission fluid
- Excessive clutch entrances
- Defective accumulator system
- Excessive wear on the valve body
- Worn internal seals and sealing rings
- Dirty MAF sensor which results to lower commanded line pressure
How to Check
Many makes such as GM, has released a technical bulletin to diagnose this code properly.
Note that, due to the transmission’s orientation, and how it sits in a vehicle, diagnosing this code will require a little bit of work to access the pressure control solenoid and the valve body.
A mechanical problem in PCS is usually caused by contamination in the valve body or wrong fluid level. Thus, these are the first ones you need to check.
Also, note that this code means a slip of 6.5 seconds or longer. Thus, there may be other reasons for this that you need to check, such as:
- Burnt clutch pack
- Worn accumulators
- Stripped overdrive clutch hub
- Worn valve, especially the actuator feed limit valve
How to Fix
If you have a mileage less of than 100K, then you may replace the pressure control solenoid and valve body.
For other causes, such as burnt clutch pack, worn accumulators, or a tripped overdrive clutch hub, then that would need disassembly and repair of the transmission. Repair for the transmission doesn’t always mean overhauling it though. In many cases, it simply means replacing the solenoid.
A popular quick remedy you can use before driving into extensive labor and expensive repair is to install a shift improver kit. These kits come with new set of accumulator spring and spacers to limit the travel of accumulator piston, which would speed up the time it takes to apply the clutch.