Hybrid ABS Issues

Hi everyone, we’ve been getting a lot of Prius models coming into the shop lately with brake actuator failure. The brake actuator is one of the “Big 3” costly replacements in the Prius and I’d argue that it’s the most dangerous repair to ignore. 

The most common scenario we hear from our customers experiencing brake actuator failure is that some or all of the dash warning lights will appear, but no noticeable symptoms occur right away. If the warnings are ignored, a long persistent buzzer sound may come and go. (Eventually it will stay on.) The buzzer is letting you know that you need to stop driving immediately. 

What is a brake actuator and why is it failing?
The brake actuator/accumulator assembly consists of a high pressure motor, a pressure tank and valves that open and close to direct brake fluid to the wheels as needed. As time progresses small leaks in the system will cause the pressure in the tank to drop which results in the motor having to run more often to maintain the pressure. Most of our customers say they’ve had no indication that there was a problem with the brakes until the warning lights came on, but in our experience when the pump can be heard about every 15 seconds or so, it may be close to failing. You can actually hear the pump trying to pressurize while the car is in ready mode (foot off the brake). If you already have warning lights on the dash its important to stop driving the car until a complete diagnostic is performed. The most common diagnostic codes for brake actuator failure is C1256 and C1391. 

When C1256 code is logged the car will enter a fail-safe mode which will disable antilock brakes, electronic braking force distribution and regenerative braking. (The first two are obvious safety concerns) but another area of issue is how this condition affects the hybrid battery. 
Normally, the engine and regenerative braking work together to charge the battery while driving, but when an ABS code is logged, the regen braking is disabled which can lead to an overly discharged hybrid battery. This is such a common problem that we often see actuator codes accompanied by battery failure codes. If you have both brake and battery codes, it is in your best interest to address the brakes first. 

If you have this code, your brake actuator will need to be replaced. Unfortunately, this is not an easy DIY repair and it can be quite costly. We do not recommend using used or remanufactured parts for the replacement due to reliability concerns. This is one area where safety overrides savings. Sites like eBay and craigslist are flooded with used actuators of varying conditions, but you’re honestly not going to know if those used parts work until after you’ve completed the lengthy installation. We only recommend purchasing a new OEM part directly from Toyota.