P0894 is a somewhat common DTC trouble code. It indicates that your GMC Sierra’s transmission may be slipping. It does not specify what part of the transmission is the problem.
While P0894 is a general diagnostic trouble code (same definition for the Sierra as any other vehicle), it is far and away most common on vehicles made by General Motors (this includes GMC).
P0894 is most commonly caused by an internal transmission failure, but there are some things you can check before sending it to the transmission shop.
P0894 Definition: Transmission Component Slipping
Your Sierra’s automatic transmission is controlled by either a TCM (transmission control module), or a PCM/ECM (Powertrain or Engine Control Module, interchangeable).
The TCM/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 how firm the shifts should be.
Input speed sensors and output speed sensors measure how fast the transmission is spinning at the beginning and end of the engine power’s trip through the transmission.
When the input speed is GREATER than what it should be in relation to the output speed, this indicates that the transmission is likely slipping, and your Sierra’s PCM will store code P0894.
P0894 Symptoms: GMC Sierra
There are almost always symptoms associated with P0894. Here are the most common ones:
- Transmission slipping– Engine RPM increases while your Sierra doesn’t speed up. Or, it speeds up less than it should.
- The smell– You will smell the smell of sulfur or rotten eggs as the friction material in the transmission’s clutch packs burn up.
- Sloppy gear engagement– The vehicle will shift and have a hard “grabbing” the next gear, or it’ll shift way too hard.
GMC Sierra P0894 Causes
Here are the most likely reasons why your GMC Sierra has P0894, as well as how to address it.
1. Check the Transmission Fluid Level
The first thing that you want to 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, switch gears, lubricate, and cool themselves. They need adequate transmission fluid pressure in order to do all of this.
If there isn’t enough fluid to do this work, the pressure inside the transmission drops, and it will start to slip.
Make sure to check the fluid on a level surface, otherwise, you may get a false reading.
2. Check the Transmission Fluid Color
Burnt or old transmission fluid loses the ability to do its job properly. The number one determinant in how fast the fluid goes bad is the conditions that you drive in.
You can use the image directly below as a rough guide to how your ATF is doing.
If your Sierra’s transmission fluid color is brown, you should consider changing it. The filter may be past its functional life and lowering pressure, which can cause slipping and P0894.
As the saying goes, “the nose knows.” If your transmission fluid smells bad, change it.
3. Wiring or Sensor Issue
The input and output speed sensors can and do fail. For instance, if you get this code and P0715 (input speed sensor circuit malfunction), you would want to address the input speed sensor first.
Wiring problems going to and from these sensors can cause a false reading as well. Do a quick inspection to confirm that everything is OK.
4. Transmission Failure
P0894 is more often than not caused by a transmission failure. It doesn’t hurt to take a quick look at the fluid and wiring. But, you’ll more than likely need to have an internal repair done by a qualified transmission shop.
Conclusion
P0894 without any other codes associated with it almost always ends up being caused by an internal transmission problem. Good luck repairing your GMC Sierra!