P0776 is a generic OBD2 code that can occur in GMC Sierra’s equipped with an automatic transmission. This code indicates that the pressure control solenoid “B” inside your Sierra’s transmission is having a performance issue, or is stuck in the off position.
P0776 Definition: Pressure Control Solenoid “B” – Performance/Stuck
Here’s the definition of P0776, divided into its two parts:
Pressure Control Solenoid “B”
Your Sierra’s automatic transmission shifts gears by changing the pressure of the transmission fluid. Transmission solenoids are responsible for facilitating this change in pressure.
Performance or Stuck
P0776 indicates that the pressure control solenoid is not doing its job the way it is supposed to or may be stuck. The code is most likely caused by a bad pressure control solenoid “b,” but there are A LOT of potential causes.
P0776 Symptoms: GMC Sierra
With this code, there will be some serious transmission performance issues. Here are the most common symptoms associated with P0776 in the GMC Sierra:
GMC Sierra: P0776 Causes + Diagnosis
Diagnosing P0776 can be a challenge at home, as pressure control solenoids are located inside the transmission. But there are a few things that you can check before you take it in to be diagnosed.
Here are the most common causes of P0776, and a solid order to check them in:
Check the Transmission Fluid
Start by checking your Sierra’s transmission fluid. Low transmission fluid can cause a drop in line pressure and can cause the pressure control solenoids not to function correctly.
The transmission fluid needs to be full AND CLEAN. If the fluid is black or shows signs that it is burnt, changing it might be enough to clear P0776.
A clogged transmission filter can cause pressure inside the transmission to drop too.
Automatic transmission fluid has a very tough job. It has to cool, lubricate, and transfer energy. It can go a long time without being changed, but if it overheats, that can be enough for it to cause P0776 in your Sierra.
Check The Wiring Harness for Damage
Check your Sierra’s wiring harness for damage. Ensure that the harness hasn’t been damaged by debris from the road. If it has, repair it, clear the code, and see if it returns.
Check for Other Codes
Check for other codes. With transmission-related codes, they will often cascade. If you have a good scanner, try and address them in the order that they were stored in the PCM’s memory.
Other codes can also give you valuable insight into the root cause of your transmission problems.
Here are some of the other causes of P0776:
- A mechanical failure inside the transmission
- Clogged passaged inside the transmission
- Pressure Control Solenoid
- Bad TCM/PCM
Bad Pressure Regulator
Clearing P0776 often involves replacing the pressure control solenoid “b”, which is outside of the abilities of most Shadetree mechanics.
Several potential issues can cause P0776 in the GMC Sierra. Before taking the car in to a professional, check the fluid level and clarity. If it’s low or bad, you might get “lucky,” and that’ll be enough to clear the code.
A good transmission shop should be able to run down the cause of this code quickly. Good luck!