What does code P0894 mean?
Code P0894 stands for Transmission Component Slipping
This code can mean either an internal transmission component is slipping, or the torque converter is slipping. The definition varies between manufacturers.
Internal transmission component slipping
A transmission manipulates torque so that power is available throughout a vehicle’s driving range. Gears are used to multiply torque. An automatic transmission uses what’s referred to as a planetary gearset. A planetary gearset consists of a sun gear, carrier and ring gear. What gear the vehicle is in depends on which part of the planetary gearset is held and which is driven.
Automatic transmission
Clutches, bands and servos are used to hold and drive the planetary gearset. When a transmission is said to be “slipping”, one or more of these devices is no longer holding. This often happens due to lack of hydraulic pressure inside the transmission.
The holding devices are applied with hydraulic pressure. Solenoids are used to control this pressure. The powertrain control module (PCM) or transmission control module (TCM) determines solenoid operation.
The PCM/TCM monitors the difference between transmission input and output speeds. Code P0894 indicates the PCM/TCM has detected a variation between these speeds, which indicates slippage.
Torque converter slipping
An automatic transmission uses what’s called a torque converter. The torque converter is a fluid coupling device used to transfer torque from the engine to the transmission. This is accomplished with the torque converter impeller, turbine and stator.
Torque converter
The impeller turns with the engine and directs fluid flow onto the turbine, which is attached to the transmission. In between the impeller and turbine, there’s a stator. The stator redirects fluid flow as it ricochets off the turbine, forcing it towards the transmission. This creates torque for the vehicle to move. When the vehicle reaches a certain speed, torque multiplication is no longer needed. At this point, the stator moves from its locked position and starts to spin freely. This is referred to as the coupling phase.
The torque converter experiences some slippage between the impeller and turbine. To overcome this, modern vehicles use a torque converter clutch (TCC). This device creates a mechanical connection between the turbine and engine. The TCC is only applied when torque multiplication is no longer needed.
Converter clutch operation is controlled by a hydraulic pressure. This is provided by the torque converter clutch solenoid.
The powertrain control module (PCM) or transmission control module (TCM) determines solenoid operation. The PCM/TCM monitors the difference between engine speed and transmission output speed. When the converter is engaged, engine speed should closely match transmission output speed. Code P0894 indicates the PCM/TCM has detected excessive TCC slippage.
P0894 symptoms
- An illuminated check engine light
- Transmission performance problems
- Poor fuel economy
- Vehicle stuck in “limp” mode
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Common causes for P0894
Code P0894 is typically caused by one of the following:
- Low transmission fluid level
- Failed control solenoid(s)
- Torque converter failure
- Internal transmission failure
- PCM/TCM problems
How to diagnose and repair P0894
The first step is to check the transmission fluid level. If the fluid is low, any leaks should be repaired and the fluid level corrected. Then, clear the code and see if it returns.
Next, perform a visual inspection. A trained eye can check for issues such as broken wires and loose connections. If a problem is found, the issue should be repaired and the code cleared. If nothing is discovered, check for technical service bulletins (TSBs). TSBs are recommended diagnostic and repair procedures put out by the vehicle manufacturer. Finding a related TSB can greatly reduce diagnostic time. TSBs are also the place to look for software updates to the PCM/TCM.
Check for other codes
If there are other codes stored, a technician will look into these first. In some cases, there may be a code stored for a specific solenoid or other serviceable component. If the part is not integral to the transmission, it can be tested and replaced if defective.
Repair or replace the transmission and torque converter
In most cases, P0894 indicates an internal transmission and/or torque converter problem. The transmission must be removed to access the converter, which attaches to the transmission oil pump. Unfortunately, when the converter fails, it usually sends debris throughout the transmission. This contaminates the transmission, making replacement or rebuilding necessary.
Likewise, the converter should be replaced when there’s an internal transmission failure. This is because metal and/or friction material from the transmission can contaminate the converter.
Other diagnostic codes related to P0894
- P0893: Code P0893 indicates the PCM has detected multiple gears engaged at the same time.
- P0895: Code P0895 indicates the PCM has detected the transmission shift time is too short.
- P0896: Code P0895 indicates the PCM has detected the transmission shift time is too long.
Code P0894 technical details
Code P0894 is often found on General Motors vehicles (Buick, Cadillac, GMC, Chevrolet) and may have accompanying technical service bulletins.
