P0894 Transmission Component Slipping
OBD-II Trouble Code Technical Description
ASE Certified Technician
总裁俱乐部appTransmission Component Slipping
What does that mean?
总裁俱乐部appThis diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Chevrolet, GMC, Mazda, Mercedes Benz, Toyota, Lexus, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
If your vehicle has stored a code P0894, it means that the powertrain control module (PCM) has received a data input signal from the input and output speed sensors which indicates that an internal transmission component is slipping.
总裁俱乐部appThe transmission control module (TCM) may be a stand alone unit but is most commonly integrated into a single housing with the engine control module (ECM). This is called the PCM.
The PCM utilizes input signals from multiple engine and transmission sensors to calculate automatic transmission shift strategy. Electronic shift solenoids are used to interrupt the flow of high pressure fluid so that the transmission may shift gears. The PCM uses voltage input signals from the transmission input speed sensor and transmission output speed sensor to determine if the transmission is functioning efficiently and without slippage.
As with many other automatic transmission malfunctions, a transmission slippage code may be caused by electrical or mechanical failure. Often when the friction material on one or more clutch discs is compromised, the transmission is not able to realize the desired gear ratio due to slippage. This condition is usually accompanied by the distinctive odor of burnt friction material in the fluid.
If the PCM detects a degree of transmission slippage that exceeds maximum allowable parameters, a code P0894 may be stored and a malfunction indicator lamp (MIL) illuminated.
What is the severity of this DTC?
总裁俱乐部appA stored code P0894 indicates that either a serious electrical issue or a catastrophic mechanical transmission failure has occurred. Conditions which contributed to a code of this nature being stored should be rectified as quickly as possible.
What are some of the symptoms of the code?
Symptoms of a P0894 trouble code may include:
- Transmission slippage
- Delayed and/or harsh gear engagement
- Erratic transmission shift patterns
- Strong odor of burnt friction material in transmission fluid
What are some of the common causes of the code?
Causes for this code may include:
- Catastrophic internal (mechanical) transmission failure
- Defective input or output speed sensor
- Shorted wiring for input speed/output speed sensors
- Faulty PCM or a programming error
What are some P0894 troubleshooting steps?
总裁俱乐部appWhen diagnosing automatic transmission codes, you should begin by making sure that the transmission fluid is clean and that the transmission if filled to the appropriate level. If the fluid level is low, locate the source of the leak and repair the condition. Refill the transmission with the recommended fluid and proceed.
总裁俱乐部appIf the fluid is excessively dark and smells strongly of burnt friction material, it will need to be replaced. This can be accomplished by removing the transmission pan (and draining the torque converter) or flushing the transmission (recommended). Either way, you will want to replace the filter at this time too. When removing the pan from the transmission, take care to preserve whatever debris may have landed therein. If the pan is relatively clear of debris you can assume that the clutches are mechanically intact. If there is an excessive amount of friction material in the pan (and stuck to the magnet), the transmission will require a rebuild from a qualified technician.
总裁俱乐部appA diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P0894. An oscilloscope may also be helpful when attempting to diagnose input and output speed sensor malfunctions.
You may use your source of vehicle information to locate a technical service bulletin (TSB) that matches the vehicle year, make, and model; as well as the engine size, code/s stored, and symptoms exhibited. If you find one, it could yield helpful diagnostic information.
With the transmission filled to the appropriate level with the recommended fluid, proceed with the first step of the diagnosis.
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.
总裁俱乐部appIf 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.
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.
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.
Use the oscilloscope (connected to the signal circuit and ground) to check for spikes and glitches in the speed sensor signal pattern.
- Most transmission slippage codes are caused by catastrophic mechanical transmission failure
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