1. Home
  2. /
  3. Complete List of OBD2...
  4. /
  5. P1811 – What Does...

P1811 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


P1811 is an OBD-II Code that refers to Maximum Adaptive & Long Term Shift


A P1811 code is a manufacturer specific diagnostic trouble code that occurs with vehicles such as Buick, Chevrolet, GM, Pontiac and related makes when the ECM/PCM detects an open circuit in the evaporative emission system purge control valve circuit. The engine absorbs extra gasoline vapors from the fuel tank, which would otherwise be vented into the environment, thanks to evaporative emission control systems known as EVAP.

The PCM monitors the voltage at the purge control valve and detects any changes in it and if notices a problem with the purge valve’s circuit, it records an error code of P1811.


Common causes for this code include:

  • Malfunctioning pressure control solenoid/EPC solenoid
  • The MAF sensor is bad, causing the commanded line pressure to be incorrect
  • Clutch is worn out
  • Accumulators are worn
  • Valve body deterioration


The symptoms of a P1811 code are:


To diagnose a P1811 DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data for failure.
  2. Visually inspect the transmission, looking for leaking seals, burnt fluid and other possible causes.
  3. Check if there is any blockage in the return line from the transmission.
  4. Test the EPC solenoid with a multimeter to see if it is getting power and ground.
  5. Test the output of the MAF sensor to see if it is sending the correct signal to the ECM.

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a P1811 code:

  • Not thoroughly inspecting all the wiring and connectors for damage.
  • Not checking the return line for blockage.
  • Not testing all the possible causes of the code.
  • Failing to look at the freeze frame data and compare it to the symptoms.

How serious is this?

A P1811 code is a serious code because it can cause the transmission to slip and shift harshly. This can lead to damage to the transmission, and potentially even engine damage if the problem is not fixed in a timely manner.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Broken or faulty wirings must be repaired or replaced
  • Any blockages in the return line must be cleared
  • A faulty EPC solenoid needs to be replaced with a new one
  • A bad MAF sensor needs to be replaced with a new one
  • A clogged transmission filter will need to be replaced
  • A worn out clutch needs to be replaced
  • Worn out accumulators need to be replaced
  • A deteriorated valve body will need to be replaced

Related codes

A P1811 is related to and may be accompanied by the following codes:

P0700 – Transmission Control System Malfunction

P1810 – TCC PWM Solenoid Circuit Open or Shorted to Ground

P0740 – Torque Converter Clutch Circuit Malfunction

P1740 – Overdrive Clutch Solenoid Circuit Fault


In conclusion, the P1811 code is a diagnostic trouble code that refers to a problem with the purge control valve circuit in the evaporative emission system. This code is a serious code that can cause the transmission to slip and shift harshly, so it is important to get it fixed as soon as possible.