2015 Toyota Prius Driver assistance Problems

Code DTC C1391 - Abnormal leak of accumulator pressure. Internal failure of the brake booster pump assembly, preventing the system from maintaining proper hydraulic pressure. This means the brakes don't work, putting the driver's and passengers' lives at risk. This DTC C1391 code and problem were reproduced and confirmed by an independent service center who specializes in 3rd generation priuses. There were warning lights that lit up when the brakes failed - the ABS, traction control, and brake light all lit up but only after the brakes had stopped working. This is a known manufacturer defect but toyota won't pay to fix it because they put a 10 year limit on first driven date or 150,000 miles. This prius only has 100k miles but toyota still won't stand behind their product even though they have admitted it was a manufacturing defect and they sold a defective product.

NHTSA ID

11756229

Incident

Aug 6, 2026

Code C1391 200k miles All the warning signs for brake booster issue came up. The cost is too high and I just missed the Customer Support Program timelines because the code came up late. This needs to be a RECALL, based on how many people experience this issue consistently.

NHTSA ID

11740166

Incident

May 6, 2026

In June 2025, while driving on the highway, the vehicle suddenly displayed multiple brake warning lights and warning messages, including the red brake warning light, ABS light, brake system warning light, and traction/slip indicator. At the same time, the brake pedal became stiff and braking effort increased suddenly, creating a near-crash situation because the vehicle did not slow normally. Before that incident, the vehicle had already been making abnormal brake-related noises, including a humming/pumping noise when the brake pedal was applied, and there were intermittent episodes where braking felt abnormal. In June 2025, the vehicle was taken to a Toyota dealership during Toyota’s brake booster support program period. The dealership documented customer complaints of “humming noise in cabin when holding foot on the brakes,” a request to “scan for codes for ZJB enhancement,” and that the “vehicle hard to accelerate and brakes got stiff,” but stated that no qualifying ABS codes were present at that time. In March 2026, the same condition returned and worsened. The vehicle again displayed the red brake warning light, ABS light, brake system warning light, and traction/slip light, and braking performance was reduced. An OBD scan of the ABS control unit showed code C1391, which is associated with brake booster / ABS actuator failure. The Toyota dealership has now diagnosed the vehicle with ABS actuator and brake booster failure and quoted repair. This is a serious safety issue because braking became more difficult while driving, including on the highway, with sudden warning lights and degraded stopping ability. The failed components are available for inspection. The problem has now been confirmed by a Toyota dealership. The issue was reported to a Toyota dealership during the prior support-program period but was not confirmed then.

NHTSA ID

11725874

Incident

Jun 15, 2025

While driving, my brakes became mushy and ineffective. Brake warning lights came on, also. It was very scary driving in rush hour traffic with little to no brakes. There was no reliability. Just keeping as much as possible space between cars, using Hazard lights &prayer.

NHTSA ID

11710539

Incident

Dec 16, 2025

The ABS failed while driving on the highway. There was no accident, but it was substantially harder to brake when needed.

NHTSA ID

11706188

Incident

Dec 19, 2025

Failure of brake pump and brake cylinder assembly system, resulting in reduced braking ability and stiff brake pedal. Per Toyota's diagnostic: trouble code C1391 is present, abnormal leak in accumulator, replaced brake ABS actuator assembly, along with brake master cylinder, and bleed the brake hydraulic system. No warning lamps or safety indicators prior to failure. Upon failure (while on freeway going 50+ MPH) the ABS, Brake, and traction control warning lamps illuminated. The failure resulted in no accident or injury, however it did occur while on the freeway going freeway speeds, and resulted in difficulty in braking, which was dangerous. Took Prius into Toyota dealer for diagnostic and repair, was told that part was known to fail in this model of Prius, and had a manufacturer designated extended warranty for 10 years or 150,000 miles. However, despite prius being under 150,000 miles, it passed ten years since purchase in march 2025, meaning I had to pay in full for the repair ($3,631.96). The car gave no indication of needing the repair until the day of the failure, which was on June 18th 2025. If the vehicle had given some prior indication of brake pump system failure or fault I would have had it repaired prior to the warranty expiration, but it did not, leaving me to pay out of pocket for a failed part that Toyota is at fault for making prone to failure.

NHTSA ID

11668371

Incident

Jun 18, 2025

I want to sale

NHTSA ID

11619659

Incident

Mar 22, 2023

ANYTIME I CHANGE ELEVATIONS THE ENGINE SEEMS TO REV WHEN IT IS IDLING ON CRUISE CONTROL. ON THE DOWNHILL, THE CAR WILL ACCELLERATE TO IGNORE THE SPEED ON CRUISECONTROL TO DANGEROUS HIGH VELOCITY. I REPORTED THIS TO TOYOTA OF NORTH HOLLYWOOD THREE TIMES... IT WAS NEVER ADDRESSED.

NHTSA ID

11351905

Incident

Dec 24, 2015

Mileage

2,000 mi

I ENTERED MY PARKED, STATIONARY PRIUS, PRESSED MY RIGHT FOOT ON THE BRAKE PEDAL, DISENGAGED THE PARKING BRAKE AND PRESSED THE ON/OFF BUTTON TO TURN THE CAR ON. MY FOOT REMAINED ON THE BRAKE PEDAL. THE ENGINE IMMEDIATELY RACED AND THE CAR BEGAN TO ACCELERATE AT HIGH SPEED. I STOMPED ON THE BRAKE PEDAL AND THE CAR KEPT MOVING. THE SOUND OF THE ENGINE WAS LOUD ENOUGH THAT PEOPLE IN NEARBY HOUSES HEARD IT. MY CAR WOULD NOT SLOW WITH MY EFFORTS TO BRAKE. I TRIED TO SHIFT INTO NEUTRAL AND PARK BUT THE CAR DID NOT SLOW DOWN. IT RACED ACROSS THE STREET AND PLOWED DIRECTLY INTO A NEIGHBOR'S STONE WALL. MY CAR BECAME WEDGED BETWEEN THE WALL AND A LARGE TREE. I HAD TO EXIT THE VEHICLE FROM THE PASSENGER SIDE AS THE DRIVER'S DOOR WAS PRESSED AGAINST THE TREE. AFTER THE COLLISION, INTERIOR LIGHTS WERE NON-FUNCTIONING EVEN WHEN THE DOOR WAS PROPPED OPEN. THE CAR WOULD HAVE CRASHED THROUGH THE HOUSE IF IT HAD NOT BEEN STOPPED BY THE WALL AND TREE.

NHTSA ID

11219137

Incident

Jun 9, 2019

Mileage

50,000 mi

NOTED RECALL ON THE NEWS FOR ELECTRICAL SYSTEM FOR 2015 TO 2018

NHTSA ID

11124500

Incident

Sep 5, 2018

I BACKED OUT OF A CARPORT AND PLACED MY CAR IN ACCELERATION AND IT PICKED UP SPEED AND THEN HIT A WALL AT AN APARTMENT COMPLEX.

NHTSA ID

11013735

Incident

May 1, 2017

Mileage

3,000 mi

TL* THE CONTACT OWNS A 2015 TOYOTA PRIUS. WHEN THE VEHICLE'S GEAR SHIFTER PARK POSITION BUTTON WAS ACTIVATED, THE ENGINE WAS TURNED ON, AND THE VEHICLE WAS UNOCCUPIED, IT ACCELERATED FORWARD ON ITS OWN. THE VEHICLE CRASHED INTO A ROCK. THE AIR BAGS HAD NOT DEPLOYED. A POLICE REPORT WAS NOT FILED AND THERE WERE NO INJURIES SUSTAINED. THE VEHICLE WAS DRIVEN HOME. THE APPROXIMATE FAILURE MILEAGE WAS 6,459.

NHTSA ID

10888762

Incident

Jul 23, 2016

Mileage

6,459 mi

TL* THE CONTACT OWNS A 2015 TOYOTA PRIUS. WHILE DRIVING APPROXIMATELY 5 TO 10 MPH AND APPROACHING THE DRIVEWAY, THE BRAKES FAILED. THE VEHICLE ACCELERATED AND CRASHED INTO A GATE. THE BRAKE PEDAL WAS RE-APPLIED AND THE VEHICLE STOPPED. THE CONTACT STATED THAT THE VEHICLE TRAVELED 20 FEET BEFORE IT STOPPED. A POLICE REPORT WAS NOT FILED AND THERE WERE NO INJURIES. THE AIR BAG FAILED TO DEPLOY. THE VEHICLE WAS TOWED TO THE DEALER FOR DIAGNOSTIC TESTING AND REPAIR. THE VEHICLE WAS NOT REPAIRED. THE FAILURE MILEAGE WAS 17,000.

NHTSA ID

10875685

Incident

Jun 17, 2016

Mileage

17,000 mi

I WAS INCHING INTO A GROCERY STORE PARKING SPOT IN MY NEW, PERFECTLY MAINTAINED 2015 TOYOTA PRIUS WHEN I EXPERIENCED UNINTENDED ACCELERATION. MY VEHICLE SHOT FORWARD AND IN A SECOND HAD CRASHED OVER A CEMENT CURB, THROUGH A FLOWER BED, AND WAS STOPPED - DESPITE MY DESPERATELY JAMMING THE BRAKE - ONLY BY SMASHING INTO A BRICK WALL. THE SUSPENSION AND STEERING ON THE CAR IS NOW SEVERELY DAMAGED, AND THE CAR CANNOT BE DRIVEN. I AM HORRIFIED: I COULD HAVE BEEN SERIOUSLY INJURED AND WORSE, HIT/HURT ANOTHER PERSON (OR AT THE VERY LEAST SEVERELY DAMAGED PROPERTY). WHAT IF I HAD CHOSEN A PARKING SPOT IN FRONT OF A GROUP OF CHILDREN?!! THEY CLOUD HAVE BEEN KILLED! THE CAR IS NOW AT A TOYOTA SERVICE CENTER WAITING FOR TOYOTA CORPORATE TO "DECIDE" IF A CAR ACCELERATING INTO A BRICK WALL OF ITS ACCORD IS A "DESIGN FLAW" THAT IT WILL PAY TO FIX. I BELIEVE THAT WHAT MAY HAVE HAPPENED IS THAT THE COMPUTER SYSTEM THAT CONTROLS THE THROTTLE/ACCELERATION EXPERIENCED A SOFTWARE BUG WHICH THREW THE CAR FORWARD. IN FACT, TOYOTA WAS FORCED PAY OUT OVER ONE BILLION DOLLARS IN FINES LAST YEAR (2014) BY THE US GOVERNMENT FOR THIS EXACT ISSUE - BUT APPARENTLY IT DIDN'T FIX ITS 2015 LINE B/F LETTING IT GO TO MARKET. I PURCHASED THE TOYOTA PRIUS BECAUSE IT WAS RECEIVED TOP SAFETY AND RELIABILITY RATINGS. ONLY NOW DO I LEARN TOYOTA HAS A HISTORY OF HIDING UNINTENDED ACCELERATION BUGS IN ITS CAR DESIGNS FOR YEARS - AND BLAMING OWNERS FOR ITS RECKLESSLY UNSAFE AND THEREBY UNETHICAL AUTO DESIGNS (NO, THIS WASN'T CAUSED BY A STUCK FLOOR MAT). I AM FURIOUS. NO ONE CAN AFFORD TO BE BLAMED FOR VEHICULAR MANSLAUGHTER DUE TO MANUFACTURER NEGLIGENCE. EVEN IF TOYOTA CLAIMS TO HAVE FIXED MY PRIUS, ITS WORD CLEARLY MEANS NOTHING AND I DO NOT TRUST THE COMPANY. I WILL BE GETTING RID OF THE CAR ASAP AND SEARCHING FOR A SAFER MODEL.

NHTSA ID

10745911

Incident

Aug 2, 2015

Mileage

1,303 mi

A BRAND NEW:2015 ONLY DRIVEN FOR TWO DAYS, WENT OUT OF CONTROL AFTER COMPLETING RIGHT TURN. DRIVER STOPPED AT RED LIGHT. TURNED RIGHT WHILE ACCELERATING WITH FULL CONTROL OF VEHICLE. COMPLETED RIGHT TURN WHILE ACCELERATING TO ATTAIN HIGHWAY SPEED IN 45 MPH ZONE. UPON COMPLETION OF TURN DRIVER TURNED STEERING WHEEL LESS THAN 2 INCHES TO DRIVERS RIGHT TO CONTINUE BEARING ON STRAIT COURSE DOWN HIGHWAY. IMMEDIATELY THEREAFTER STEERING WHEEL SHUDDERED, AND STEERING WHEEL ROTATED HARD TO THE RIGHT FOR WHAT SEEMED LIKE A 110 PLUS DEGREE ROTATION. THE PRIUS OUT OF CONTROL VEERED SHARPLY TO THE RIGHT AND SMASHED INTO CURB. DRIVER INJURED BACK, HAND, AND FOOT. ...UPDATED 03-11-15 *BF

NHTSA ID

10679356

Incident

Nov 28, 2014

Mileage

400 mi