Technical Description of OBD-II Trouble Code
Excessive Clutch Slippage
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Audi, Volkswagen, Volvo, BMW, and others. While it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
If your vehicle has stored a code P0811, it means that the powertrain control module (PCM) has received a data input signal from the input and output speed sensors indicating excessive clutch slippage.
The transmission control module (TCM) may be a separate unit, but it is commonly integrated into a single housing with the engine control module (ECM), known as the PCM.
The PCM uses input signals from various engine and transmission sensors to calculate the maximum allowable degree of transmission (clutch) slippage. Excessive clutch slippage can be caused by wear on the clutch disc and pressure plate, as well as mechanical failure. The PCM uses voltage input signals from the transmission input speed sensor and transmission output speed sensor to determine if the clutch is functioning within the parameters for maximum allowable slippage.
Similar to other transmission malfunctions, a clutch slippage code can be caused by electrical or mechanical failure. When the friction material on the clutch disc is worn down below a certain level, the clutch starts to slip. This condition is often accompanied by the distinct odor of burnt friction material.
If the PCM detects a degree of transmission (clutch) slippage that exceeds the maximum allowable parameters, a code P0811 may be stored and the malfunction indicator lamp (MIL) will illuminate. Multiple ignition cycles (with a failure) may be required for MIL illumination.
What is the severity of this DTC?
A stored code P0811 indicates that either a serious electrical issue or some type of clutch failure has occurred. In any case, it is important to rectify the conditions that led to the storage of this code as quickly as possible.
What are some of the symptoms of the code?
Symptoms of a P0811 trouble code may include:
What are some of the common causes of the code?
Causes for this code may include:
What are some P0811 troubleshooting steps?
Before attempting to diagnose a P0811, ensure that the clutch, pressure plate, and throwout bearing are functioning properly. Also, check clutch arms and bushings, as well as clutch hydraulics if applicable.
To diagnose a code P0811, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle-specific diagnostic information. An oscilloscope may also be helpful for diagnosing input and output speed sensor malfunctions.
You can use your source of vehicle information to find a technical service bulletin (TSB) that matches the vehicle year, make, and model, as well as the engine size, stored code/s, and exhibited symptoms. If you find one, it may provide helpful diagnostic information.
With the clutch functioning properly, proceed with the first step of the diagnosis.
Step 1
Use the scanner (connected to the vehicle diagnostic connector) to retrieve all stored codes and relevant freeze frame data. It is advisable to write down this information 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 more difficult to diagnose. In such cases, the conditions that led to the storage of the code may need to worsen before an accurate diagnosis can be made.
Step 2
If the code is immediately reset, the next step in your diagnosis will involve searching your vehicle information source for diagnostic flowcharts, connector pin-out charts, connector face views, and component testing procedures/specifications.
Step 3
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.
Step 4
Use the oscilloscope (connected to the signal circuit and ground) to check for spikes and glitches in the speed sensor signal pattern.
