P0868 is a generic DTC code, which means it has the same definition for the Buick Rainier as it would any other vehicle. This particular code indicates that the transmission fluid pressure is below the minimum operating specs.
If your Rainier has P0868 the first thing you should do is check the transmission fluid. If it’s really low, there won’t be enough pressure in the transmission for it to function properly. Other issues can cause P0868, but making sure that the transmission fluid level is full will minimize any potential damage if that ends up being the problem.
Don’t Ignore Low Transmission Fluid
Your Buick Rainier’s transmission is a mechanical device that transfers rotational motion to another location. Automatic transmissions use complex mechanisms to perform this task more efficiently, but they are still fundamentally doing the same job as a manual transmission.
But, an automatic transmission is a lot more complex than a manual. It uses transmission fluid as a hydraulic fluid to activate solenoids, switch gears, lubricate, and cool itself. An automatic needs adequate transmission fluid pressure in order to do all of this. If there isn’t enough, it’ll burn up and you’ll need a new one, or you’ll have to have it rebuilt.
P0868 Symptoms: Buick Rainier
Usually, there will be noticeable symptoms related to P0868 in the Rainier. Here are the most common ones.
- Slippage– The most noticeable symptom of low transmission fluid pressure is slippage (rpm goes up, but not speed). If it starts slipping, whether on acceleration or when coming to a stop, this means that there is not enough transmission fluid pressure to move the vehicle properly.
- Leaking Transmission Fluid– Look under where you park your Rainier regularly. Check to see if there are any puddles or fresh drops of transmission fluid. It should be anywhere between a red and brown color, depending on how many miles it has seen and how harsh the conditions you drive in are.
There very well may be no noticeable symptoms at all. This may indicate that the transmission fluid needs to be changed or that the transmission fluid pressure sensor is bad (we’ll cover more on that below).
Buick Rainier: P0868 Causes + Diagnosis
Here are the most common causes of P0868 in a (somewhat) logical order to approach them in.
Check Transmission Fluid
You’ll need to check your Rainier’s transmission fluid to make sure that it is full. Make sure to do it on a level surface.
Even if it is full, it may not be able to do its job properly if it has been burnt and overheated. Or, maybe there’s just too much mileage on the fluid.
Fluid issues are the most common cause of P0868.
If your Buick Rainier has gone too long without having the transmission fluid and filter changed, a clogged filter can cause the transmission fluid pressure to drop. The transmission fluid pressure sensor will pick up on this, and P0868 will be thrown.
Inspect the wiring harness going to the transmission fluid pressure sensor. If it looks like it has been damaged, it’ll need to be replaced.
The location of the transmission fluid pressure sensor and the distance it must travel makes it more prone to damage than most other wiring in the vehicle.
Other Potential Causes of P0868
- Bad transmission pump
- Bad transmission fluid pressure sensor
- Bad transmission temp sensor
- Internal transmission parts failure
As you can see, quite a few issues can cause P0868 in the Buick Rainier. Most of the time, it’ll be fluid related though. Good luck!