C1391 on 2012-2016 Toyota Prius V: Brake Actuator Leak and Repair Guide

What's Unique About the 2012-2016 Toyota PRIUS V

The Toyota Prius V, like other Toyota hybrids, uses a sophisticated electro-hydraulic brake system (ECB) instead of a traditional vacuum brake booster. This system is necessary for blending regenerative braking (to charge the hybrid battery) with conventional hydraulic braking. The core of this system is the brake booster and pump assembly, which is a single, complex, and expensive unit. This assembly has a known history of internal failures across several Toyota and Lexus hybrid models, including the Prius V, leading to code C1391.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Multiple warning lights on the dashboard, including BRAKE, ABS, and TRAC (traction control).
• A "Check VSC" message may appear on the multi-function display.
• A buzzing, humming, or pulsing sound from the engine bay, which is the brake booster pump running excessively (e.g., every 5-15 seconds) to compensate for the leak. [ODI 11616427, 9, 12, 29]
• A change in brake pedal feel, such as being soft, spongy, or vibrating when pressed. [4, ODI 11655151, 12]
• Reduced stopping power or intermittent brake failure.
🎬 Watch: Why these hybrid brake systems fail and what it costs.
• A hissing sound of escaping pressure after the vehicle is turned off.

Most Likely Causes

1. Internal Failure of the Brake Booster and Pump Assembly 🔴 High Probability These assemblies are known to develop internal leaks in the accumulator or have pump motor failures over time, a weakness noted in several Toyota hybrid models of this era. The failure is due to internal seals degrading, causing pressurized fluid to leak back to the reservoir instead of being held for braking.
   How to confirm: A mechanic will use a diagnostic scan tool like Toyota Techstream to monitor the accumulator pressure sensor data. A rapid drop in pressure confirms an internal leak. Listening for the pump cycling on and off frequently (every 15-30 seconds or less) with the car on but not being driven is another strong indicator. An owner on PriusChat noted you can sometimes see the fluid level in the reservoir rise and fall as the pump cycles and the fluid leaks back.
   Typical fix: The entire Brake Booster Assembly with Master Cylinder and the Brake Booster Pump Assembly must be replaced as a unit, as per Toyota's official repair procedure outlined in TSBs and Customer Support Programs.
   Est. part cost: $1800-$3500

Rare But Worth Checking

• Low Brake Fluid: While a low fluid level can trigger braking system faults, it's rarely the root cause of C1391, which points to an internal pressure leak, not necessarily a fluid volume issue. However, it should always be checked first.
• Wiring or Connector Issues: Damage to the wiring harness or corrosion at the connector for the brake actuator assembly could theoretically cause a fault, but it is far less common than the actuator itself failing.

Diagnosis Steps

1. Verify the presence of C1391 and any other related codes (C1252, C1253, C1256) using a Toyota-compatible OBD-II scanner.
2. With the vehicle on (in 'Ready' mode), listen for the brake pump motor in the engine bay. Note if it runs constantly or cycles on and off every few seconds. A cycle time of less than 30 seconds is a strong indicator of a leak.
3. Check the brake fluid reservoir to ensure the level is at the MAX line.
4. Using an advanced scan tool (like Toyota Techstream), access the live data for the Skid Control ECU and monitor the accumulator pressure sensor voltage. A rapid drop in voltage when the pump is not running confirms an internal leak.
5. Inspect the wiring harness and connectors leading to the brake actuator assembly for any visible damage or corrosion.
6. If the pressure test fails and wiring is intact, the brake booster/pump assembly is faulty and requires replacement. 🎬 See this step-by-step walkthrough of the booster and actuator replacement. There is no component-level repair for the internal leak.

Parts You'll Likely Need

• Brake Booster and Master Cylinder Assembly (OEM #47050-47110) — This is the main component that fails, containing the master cylinder, accumulator, and control unit where the internal leak occurs. It is replaced as a complete assembly.
  Trusted brands: Toyota (OEM)
  OEM price range: $1300-$2500
  Aftermarket price range: Not generally available
• Brake Booster Pump Assembly (OEM #47070-12020) — This is the electric pump that generates hydraulic pressure. It is typically replaced along with the booster assembly as recommended by Toyota's repair procedures. An alternative part number is 47070-47060.
  Trusted brands: Toyota (OEM), Aisin
  OEM price range: $600-$1000
  Aftermarket price range: $400-$700

Related Codes That Often Appear With This One

• C1256 — This code means 'Accumulator Low Pressure.' It frequently appears with C1391 because the internal leak (C1391) directly causes the low pressure condition (C1256).
• C1252 — This code indicates 'Brake Booster Pump Motor On Time Abnormally Long.' The pump runs excessively to try and compensate for the pressure leak, triggering this code.
• C1253 — This code points to a 'Brake Booster Pump Motor Relay Malfunction.' It can be stored alongside the other codes as the system tries to manage the failing pump.
• C1249 — This code for 'Stop Light Switch Circuit Malfunction' was reported in one NHTSA complaint alongside C1391, suggesting a potential related fault in the broader braking circuit. [ODI 11469216]

Technical Service Bulletins (TSBs) & Recalls

• T-SB-0089-20: For 2012-2014 Prius V, this bulletin details the diagnosis and repair procedure for DTCs C1391, C1252, C1256, or C1253 caused by an internal brake fluid leak in the brake booster assembly. It specifies replacing both the booster and pump assemblies.
🎬 Watch: A professional guide to replacing the booster and accumulator.
• T-SB-0115-20: This TSB also addresses the same set of codes (C1391, C1252, C1256, C1253) for the 2015 Prius V, indicating the problem can extend beyond the years covered by the CSP. It confirms the cause is a small internal brake fluid leak in the booster assembly.

Platform-Specific Known Issues

• Toyota issued a Customer Support Program (CSP) 20TE07 for 2012-2014 Prius V models for this exact issue. This program extended the warranty coverage for the brake booster and pump assemblies. It had two phases: Primary Coverage (until Dec 31, 2021) and Secondary Coverage (10 years or 150,000 miles from the date of first use). As of now, most vehicles are outside this coverage period due to age. Owners had to have one of the specific codes (C1391, C1252, C1256, or C1253) for the repair to be covered.
• NHTSA records contain multiple owner complaints about this specific failure, noting symptoms like a "pulsing air sound" and a vibrating brake pedal, with repair quotes exceeding $4,000. [ODI 11616427, ODI 11668719]
• One owner reported to the NHTSA that their vehicle was just outside the warranty extension criteria and they were forced to pay $3,886.09 for the repair. [ODI 11353015]

Mechanic-Grade Diagnostic Values

• Accumulator Pressure Sensor Voltage (ACC PRESS SENS 1) — expected: 3.2 to 4.0 V (with pump motor stopped and no braking).. Failure: Voltage drops steadily without the brake pedal being applied, indicating an internal pressure leak.
• Skid Control ECU Power Supply Voltage — expected: 11 to 14 V at all times.. Failure: Voltage below 11V can indicate a power supply issue to the module.
• Skid Control ECU Ground Resistance — expected: Below 1 Ω.. Failure: Resistance above 1 Ω indicates a poor ground connection, which can cause various faults.

Scan Tool Commands That Help

• Toyota Techstream: Air Bleeding (after actuator replacement) — This is a mandatory step after replacing the brake booster/actuator assembly. The procedure must be initiated via the scan tool to properly bleed the system and 'unlock' the new unit, allowing it to accept calibration.
• Toyota Techstream: Linear Valve Offset Calibration — This must be performed after replacing the brake booster assembly or after the air bleeding procedure. It calibrates the solenoid valves to ensure proper brake feel and operation. Failure to perform this step will leave warning lights on and can result in other codes like C1345.
• Toyota Techstream: Reset Memory (in ABS/VSC/TRAC Utility) — Used to clear stored calibration data before performing a new Linear Valve Offset Calibration, especially if previous attempts have failed or if other related codes are present.
• Toyota Techstream: Data List -> ACC PRESS SENS 1 — Used during diagnosis to monitor the live accumulator pressure sensor voltage. This is the primary method to confirm a pressure leak by observing the voltage drop over time with the brakes not in use.

Wiring & Ground Locations

• A19 Connector (Skid Control ECU) — The main electrical connector on the brake actuator assembly itself, located in the engine bay on the firewall.. This is the central connection point for all power, ground, and communication signals for the brake control system. Technicians test for power and ground integrity here.
• A19-46 (IG1) - Body ground — Pin 46 on the A19 connector at the Skid Control ECU.. This is the ignition power supply pin. It should have 10-14V with the ignition ON. A loss of voltage here would render the entire module inoperative.
• A19-1 (GND2) & A19-32 (GND1) - Body ground — Pins 1 and 32 on the A19 connector at the Skid Control ECU.. These are the primary ground pins for the module. Resistance should be below 1 Ω. A bad ground can cause erratic behavior and false codes.

Real Owner Repair Stories

• PriusChat user 'Zurab Laliashvili' (2010 Toyota Prius (Gen 3, similar system)) — Four warning lights on the dash (ABS, brake, skid, !) and code C1391. The actuator noise was occurring every 5 to 10 seconds.
  ❌ Tried (didn't work) Initial diagnosis confirmed the common failure.
  ✅ What actually fixed it Replaced the brake actuator and pump with used parts from a 2013 Prius. After installation, the mechanic had to perform a software update for an additional $60 because the replacement parts were from a newer model year. The final fix required both the parts replacement and the software update to clear all lights. Total cost was $572 for used parts and labor.
• YouTube channel 'Yesvin's Automotive' (3rd Gen Toyota Prius (similar system)) — ABS, exclamation mark, skid control, and brake lights on. Constant buzzing from the brake pump. Code C1391 stored.
  ❌ Tried (didn't work) Simply replacing the part is not enough.
  ✅ What actually fixed it The brake actuator assembly was replaced. Crucially, the fix required using a scan tool to perform the 'Air Bleeding' utility after replacement. The video emphasizes that the system must be told via the scanner that a bleed has occurred to 'unlock' the new unit. After the bleed, the 'Linear Valve Offset' calibration was performed, which successfully cleared all codes and warning lights.

OEM Part Supersession History

• 47050-47110 → 47050-47110 is the current correct part number for 2012-2014 Prius V. — This part number is consistently referenced by Toyota parts dealers for the 2012-2014 Prius V.
  Heads up: While other part numbers like 47050-47060 or 47050-47140 exist for other Prius models, 47050-47110 is specified for the Prius V in the affected years.

Model Year Variations Within This Range

• 2012-2014: These model years were specifically covered by Toyota's Customer Support Program 20TE07 for the C1391 fault, indicating a higher prevalence or earlier acknowledgment of the issue for these years.
• 2015: The 2015 model year was not included in CSP 20TE07 but is addressed for the same codes (including C1391) in a separate Technical Service Bulletin (T-SB-0115-20), confirming the failure mode extends to this year but was not covered by the same warranty extension program.