What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). This 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 the year, make, model, and powertrain configuration.
If your vehicle has stored a P0894 code, it means that the powertrain control module (PCM) has received a data input signal from the input and output speed sensors indicating that an internal transmission component is slipping.
The transmission control module (TCM) may be a standalone unit but is most often integrated into a single housing with the engine control module (ECM). This is referred to as the PCM.
The PCM uses input signals from multiple engine and transmission sensors to calculate the automatic shift strategy. Electronic shift solenoids are used to interrupt the flow of high-pressure fluid so the transmission can shift gears. The PCM uses voltage input signals from the transmission input speed sensor and the transmission output speed sensor to determine if the transmission is operating efficiently and without slipping.
As with many other automatic transmission malfunctions, a transmission slip code can be triggered by an electrical or mechanical failure. Often, when the friction material on one or more clutch discs is compromised, the transmission is unable to achieve the desired gear ratio due to slipping. This condition is usually accompanied by the distinctive smell of burnt friction material in the fluid.
If the PCM detects a degree of transmission slip that exceeds the maximum allowable parameters, a P0894 code may be stored and a malfunction indicator lamp (MIL) illuminated.
How severe is this DTC?
A stored P0894 code indicates that a serious electrical issue or a catastrophic mechanical transmission failure has occurred. The conditions that contributed to the storage of a code of this nature should be rectified as soon as possible.
What are some of the symptoms of the code?
Symptoms of a P0894 trouble code may include:
- Transmission slipping
- Delayed and/or harsh equipment engagement
- Irregular transmission shifting patterns
- Strong smell of burnt friction material in the transmission fluid
What are some common causes of the code?
Causes
of this code may include:
- Catastrophic internal (mechanical) transmission failure
- Faulty input or output speed sensor
- Shorted wiring for the input/output speed sensors
- Faulty PCM or programming error
What are the troubleshooting steps for P0894?
When diagnosing automatic transmission codes, you should start by ensuring the transmission fluid is clean and the transmission is 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.
If the fluid is excessively dark and has a strong smell of burnt friction material, it will need to be replaced. To do this, remove the transmission pan (and drain the torque converter) or flush the transmission (recommended). In either case, you will also want to replace the filter at this time. When removing the transmission pan, be sure to save any debris that may have landed in it. If the pan is relatively free of debris, you can assume 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 rebuilding by a qualified technician.
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle-specific diagnostic information will be required to diagnose a P0894 code. An oscilloscope may also be helpful when attempting to diagnose input and output speed sensor malfunctions.
You can use your vehicle information source to locate a technical service bulletin (TSB) that matches the vehicle’s year, make, and model; as well as engine size, stored codes, and presented symptoms. If you find one, it may provide useful diagnostic information.
With the transmission filled to the appropriate level with the recommended fluid, proceed to the first step of diagnosis.
Step 1
Use the scanner (connected to the vehicle’s diagnostic connector) to retrieve all stored codes and relevant freeze frame data. It is a good idea to record this information before clearing the codes, then test drive the vehicle until the PCM enters readiness mode or the code resets.
If the PCM enters readiness mode at this point, the code is intermittent and may be much more difficult to diagnose. If this is the case, the conditions that contributed to the code being stored may need to worsen before an accurate diagnosis can be made.
Step 2
If the code immediately resets, the next step in your diagnosis will require you to look up diagnostic flowcharts, connector pinout diagrams, connector face views, and component testing procedures/specifications in your vehicle information source.
Step 3
Use the DVOM to test the voltage, ground, and signal at the transmission input and output speed sensors (key on, engine off). The 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 dips in the speed sensor signal pattern.
Most transmission slip codes are caused by catastrophic mechanical transmission failure