Error Code P0811 is defined as Excessive Clutch Slippage. Error Code P0811 is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made from 1996 up to present. This includes vehicles from, but not limited to, Audi, BMW, Volkswagen, Volvo, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary between make, model, and powertrain configuration.

The TCM (transmission control module) is sometimes a standalone unit. In recent years, however, it’s been commonly integrated into the single housing of the ECM (engine control module). This component is now referred to as the PCM.

To calculate the maximum allowable degree of transmission (clutch) slippage, the PCM uses input signals from multiple engine transmission. Excessive clutch slippage happens when there are a clutch disc and pressure plate wear, as well as mechanical failure. To find out if the clutch is working properly within the parameters for the maximum allowable stoppage, the PCM uses voltage input signals from different sensors, namely the transmission input speed sensor and transmission output speed sensor.

As with many transmission-related error codes, the clutch slippage code may be caused by an electrical or mechanical failure. Often, the friction material on the clutch disc becomes worn, and at a certain level, the clutch will start to slip. When this problem happens, it is usually accompanied by a distinct odor coming from the burnt friction material.

If the PCM determines a degree of transmission (clutch) slippage that goes beyond the maximum allowable parameters, then the Error Code P0811 will be set, and simultaneously illuminate the Check Engine lamp. In some cases, multiple ignition cycles may be needed (with failure) before the Check Engine light is activated.

Common Symptoms

  • Transmission slippage
  • Clutch engagement happens near the top
  • Harsh gear engagement
  • Strong burnt odor from friction material

Possible Causes

  • Faulty input or output speed sensor
  • Worn clutch disc or pressure plate
  • Short in the wiring of input speed or output speed sensors
  • Defective or programming error in the PCM

How to Check

Before starting your diagnosis for this error code, make sure the clutch, pressure plate, and the throwout bearing are working properly. If possible, you also need to inspect the clutch arms, bushings, and clutch hydraulics.

You will also need a diagnostic scanner, DVOM (digital volt/ohmmeter), and a source of vehicle diagnostic information. An oscilloscope can also help in diagnosing the malfunctions in the input and output speed sensor.

Use the vehicle’s information to find the TSB (technical service bulletin) that matches the specifics of the vehicle (make, model, engine size, symptoms, and codes stored). This could help for a more thorough diagnosis.

With clutch properly working, you can proceed with the next step of the diagnosis.

First Step

Use the scanner (connected to the vehicle diagnostic connector) to retrieve all stored codes and pertinent freeze frame data. It is a good idea to write this information down before clearing the codes then test-drive the vehicle until the PCM either enters readiness mode, or the code is reset.

If the PCM enters readiness mode at this time, the code is intermittent and may be much more difficult to diagnose. If this is the case, the conditions which contributed to the code being stored may need to worsen before an accurate diagnosis can be made.

Second step

If the code is immediately reset, the next step of your diagnosis will require that you search your vehicle information source for diagnostic flow-charts, connector pin-out charts, connector face views, and component testing procedures/specifications.

Third step

Use the DVOM to test voltage, ground, and signal at the transmission input and output speed sensors (key on and engine off). Input and output speed sensor circuits typically consist of a reference voltage, a signal wire, and a ground.

Fourth step

Use the oscilloscope (connected to the signal circuit and ground) to check for spikes and glitches in the speed sensor signal pattern.

Excessively worn clutch components cause most transmission slippage codes.

How to Fix

  • Repair corroded, disconnected, or frayed electrical connectors or wirings
  • Replacement of clutch position sensor
  • Replacement of PCM (rare)

This error code indicates a serious electrical problem or a clutch failure. This is considered a serious problem and must be addressed as soon as possible.