C1391: Abnormal Leak in Accumulator [Quick Fix]

The C1391 error code appears when there is a leak in the brake actuator or the brake booster pump. It causes brake fluid to leak out, making the brakes less effective. It could be something as simple as a faulty seal or more serious. In any case, it’s critical to have it checked out by a professional mechanic as soon as possible to keep your vehicle running safely.

I had the same problem with the c1391 “Abnormal Leak in Accumulator Code” in my 2009 Prius for about seven years. It was so annoying, making this grinding sound whenever I drove over bumps.

I thought there must be an easier way to make my car run typically again, and when I finally fixed it, it was straightforward! So I decided to help other Prius drivers avoid the pain of this leak.

Read on to learn how to fix and troubleshoot the c1391 abnormal leak in the accumulator in my Prius and make your car run great again!

What does the code C1391 mean?

C1391 is the DTC (diagnostic trouble code) for accumulator leaks in the Prius. This code is stored if a brake fluid, internal, or other leak is detected in the actuator due to improper sealing. The term “leakage” refers to the loss of fluid from one area of the vehicle to another.

The C1391 code is a diagnostic trouble code (DTC) set when the ECM detects an abnormal leak in the accumulator of the vehicle’s hybrid system.

The C1391 code indicates the presence of abnormal air in the accumulator pressure control system. If a brake fluid, internal, or other leak is detected due to improper actuator sealing, this information is saved in the diagnostic trouble code. Internal leakage is suspected if the pump motor runs continuously without stopping.

Most Common Cause for The Code C1391 to Display?

The C1391 display code is commonly caused by the following:

• Brake Actuator Assembly: A common cause of code C1391 Toyota is a leak in the brake actuator assembly. If this occurs, a leak will be evident on the brake pedal. An electrical fault usually causes this problem with the circuit board that controls the operation of the pump motor.

• Fluid Leakage: C1391 is the diagnostic trouble code. Toyota may also alert you to faulty brake fluid level sensors, which can result in excessive fluid levels in your vehicle’s reservoirs. The brake fluid level sensor is located on each rear wheel well and measures the amount of hydraulic pressure at each wheel.
  When a tire is inflated with air pressure, it measures how much air is trapped between its two chambers. Excess fluid will flow into these chambers if too much air is trapped, reducing their ability to hold pressure. If you have a leak in your brake fluid and have had it checked by a mechanic, it is most likely a brake actuator failure.

• Brake Actuator Assembly Circuit: Faulty wiring or connections within the system that controls the C1391 Toyota Prius are another cause. It’s not uncommon for wires in this system to become loose or disconnected over time, resulting in intermittent electrical problems with your vehicle’s braking system and other systems like cruise control.
  This usually means a problem with the wiring between the brake actuator assembly and the central computer system (ECM).

• Faulty Seal: A bad seal is another cause of the C1391 abnormal leak in the accumulator. Between the accumulator and the valve body is where the seal is located. If this seal leaks, air will enter, causing your car to overheat and run hot. When you drive your car, you may notice a small amount of oil leaking out, leaving a stain on your driveway or garage floor.

• Brake Actuator Assembly Harness is Open or Shorted: Another possibility is that the brake actuator assembly harness is open or shorted. Overheating or corrosion on the wires and connectors in this area can also cause this fault, which is uncommon.

C1391 Code Troubleshooting Tips 

Here are a few troubleshooting tips to help diagnose the issue with the brake system on your vehicle:

1. Inspect the brake fluid level; ensure it is at the appropriate level; if it is low, it could indicate a leak.
2. Check the brake hoses and lines; look for any signs of wear or damage, such as cracking, fraying, or leaking.
3. Take a look at the brake pads. Worn or damaged brake pads can lead to a decrease in braking performance.
4. Check the brake calipers. Ensure that the brake calipers are functioning properly; they can sometimes get stuck, which can also decrease braking performance.
5. Have the brake booster, brake actuator, or brake booster pump inspected; if the problem seems to be with any of these components, you should bring the vehicle to a professional mechanic, as those require more specific tools and experience.

It’s important to keep in mind that diagnosing the cause of an issue like this can be difficult, and it might require the help of a professional mechanic to identify the problem correctly. Always exercise caution when working on your vehicle’s braking system; if unsure, always seek professional assistance.

CONCLUSION

The C1391 code displays when there are leaks from internal components other than the actuator pump (like a heater hose), excessive wear on seals and/or hoses, or leaks inside the actuator itself.

If you experience any of these symptoms, then you must have your vehicle inspected immediately and, if necessary, repaired.