P0894 is a somewhat common DTC trouble code. This indicates that your transmission may be slipping. It doesn’t specify which part of the transmission is the problem.
Although P0894 is a general diagnostic trouble code (same definition for any vehicle), it is by far the most common on GM-made vehicles (and the 4L60E and 4L80E transmissions). You will occasionally see it on Mercedes and some Ford vehicles.
P0894 is most commonly caused by an internal transmission failure, but there are a few things you can check before sending it to the transmission shop.
P0894 Definition: Transmission component slippage
Your vehicle’s automatic transmission is controlled by a TCM (transmission control module) or a PCM/ECM (engine or powertrain control module, interchangeable).
The TCM or PCM uses data from the engine control systems (such as RPM, engine load, speed, etc.) to determine what gear the vehicle should be in, whether or not to lock the torque converter and the firmness of the changes.
There are input speed sensors and output speed sensors that measure the rotational speed of the transmission at the beginning and end of the engine’s power travel through the transmission.
When the input speed is HIGHER than it should be relative to the output speed, this indicates that the transmission is probably slipping, and the PCM will store code P0894.
There are almost always symptoms associated with P0894. Here are the most common ones:
- Transmission slip– Engine RPM increases while vehicle speed does not.
- The smell– You will smell a sulfur or rotten egg odor when the friction material in the transmission clutch packs burns off.
- Careless gear engagement– The vehicle will change gears and will have a hard time “catching” the next one, or it will change with too much force.
Here are the most likely reasons why your vehicle has P0894, as well as how to fix it.
1. Check the transmission fluid level
The first thing you should do when your vehicle has P0894 is to check the transmission fluid.
Automatic transmissions use transmission fluid (ATF) as a hydraulic fluid to activate solenoids, shift gears, lubricate, and cool. They need adequate transmission fluid pressure to be able to do all of this.
If there is not enough ATF to do this job, the pressure inside the transmission decreases, and it will begin to slip.
Make sure you check the fluid on a level surface, otherwise, you may get a false reading.
2. Check the color of the transmission fluid
Burnt or old transmission fluid loses its ability to do its job properly. The determining factor in how quickly the fluid goes bad is the conditions in which you drive.
You can use the image below as a rough guide to how your ATF is doing.
If the color of your transmission fluid is brown, you should consider changing it. The filter may have outlived its useful life and reduced pressure, which can cause slippage and P0894.
As the saying goes, “The nose knows.” If your transmission fluid smells bad, change it.
3. Wiring or sensor problem
Input and output speed sensors can and do fail. For example, if you get this code and P0715 (input speed sensor circuit malfunction), you should treat the input speed sensor first.
Wiring problems going to and from these sensors can also cause a false reading. Do a quick inspection to confirm that everything is okay.
4. Transmission failure
P0894 is usually caused by a transmission failure. It doesn’t hurt to take a look at the fluid and wiring. But you will most likely have to do an internal repair at a qualified transmission shop.