C1391 on Toyota: How to Diagnose & Fix
Abnormal Leak of Accumulator Pressure (manufacturer-specific)
4 Toyota models · 5 documented issues · 5 critical · $1,200-$3,500 repair
C1391 on Toyota by model: symptoms, diagnosis and fix
On 4th-gen 4Runners the integrated ABS actuator/brake master cylinder assembly (with electric pump motor and accumulator) fails internally. The pump motor or accumulator wears out so the pump never reaches pressure and runs continuously; owners get simultaneous ABS, BRAKE, VSC and TRAC warning lights, a loud continuous in-cabin alarm, electronic noise when braking, and a hard or sinking pedal with reduced assist. It is a safety-relevant failure and the assembly is one of the most expensive non-drivetrain parts on the truck. This is distinct from the brake booster/master-cylinder internal-leak issue: this is the ABS hydraulic actuator/accumulator unit.
Common Symptoms
- ABS, BRAKE, VSC and TRAC lights on together
- Loud continuous in-cabin warning alarm
- Brake pump motor runs constantly / electronic noise
- Hard or sinking brake pedal, reduced assist
- C-series ABS/brake control codes
How to Fix
First scan and inspect the wheel-speed (ABS) sensors and connectors, as dirty/damaged sensors mimic the symptoms cheaply. If the fault is the actuator/accumulator (continuous pump run, pressure faults), replace the integrated ABS actuator with master cylinder assembly - OEM 47050-60080/47050-60081 (4th gen) - and bleed/initialize the system with a capable scan tool. The part alone runs roughly $1,700-$2,300; remanufactured units are available cheaper.
Sources for this issue (2)
Multiple 4th-generation 4Runner owners report the brake pedal becoming hard, requiring excessive effort to stop, often accompanied by ABS/VSC/TRAC warning lights and a buzzing or continuously running brake actuator. Toyota issued service information for brake booster pump/master cylinder concerns on related platforms, and owner complaints frequently describe internal accumulator or actuator failure rather than simple pad/rotor wear. Repairs are expensive because the booster/master/actuator assembly is typically replaced as a unit.
Common Symptoms
- Hard brake pedal
- Longer stopping distance
- ABS light on
- VSC TRAC light on
- Brake warning light on
- Buzzing or frequently running brake pump
- Intermittent loss of brake assist
How to Fix
Diagnose by scanning the ABS/VSC system for stored brake actuator codes, checking whether the pump runs excessively, and verifying loss of assist with the engine running. Inspect for internal hydraulic leakage and confirm whether the accumulator pressure will not hold. Repair usually involves replacing the brake booster assembly and/or master cylinder actuator unit, followed by brake bleeding with a scan tool-capable procedure and calibration of the brake system.
Owner tips & cautions
- TipScan the ABS/VSC module before replacing parts; many owners initially chase wheel speed sensors when the real fault is the booster/actuator assembly.
- TipIf the pump runs every few seconds with the key on, do not ignore it; owners report the condition usually worsens into warning lights and reduced assist.
Sources for this issue (2)
The regenerative-braking brake actuator (the integrated ABS/booster/accumulator pump module) is a known weak spot on the Highlander Hybrid. The accumulator develops an internal leak and the pump runs constantly, triggering a loud, repetitive whirring/buzzing and warning lights; in some cases brake assist is reduced, which owners describe as a serious safety concern (the same family of actuators drove early Prius brake recalls). CarComplaints documents repeated brake actuator complaints on the 2006 Highlander Hybrid, and the repair is rarely covered out of warranty.
Common Symptoms
- Constant brake pump motor whirring/buzzing
- Brake, ABS, VSC and hybrid warning lights
- Hard or reduced brake assist
- Longer stopping distance
How to Fix
Replace the integrated brake actuator assembly and re-initialize/program it with Toyota Techstream (the new unit must be calibrated and bled). For the 2006-2007 Highlander Hybrid the actuator is Toyota PN 44050-48191; 2008-2013 use 44050-48320 — verify by VIN. This is expensive: the part alone runs ~$1,200-$1,800 and full dealer replacement quotes range from roughly $2,600 to $3,500+. Independent hybrid specialists can be cheaper.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota 44050-48191 genuine brake actuator/modulator
first-generation actuator replacement only after Toyota brake-system diagnosis condemns the integrated modulator assembly Fitment/availability: VIN-confirmed 2006-2007 Highlander Hybrid 3.3L MHU23/MHU28 branch; replaces 44050-48190 Fitme…
- Toyota 47070-48020 genuine brake-booster pump/accumulator assembly
pump/accumulator replacement when accumulator leakage or pump failure is proven by the Toyota diagnostic procedure Fitment/availability: VIN-confirmed 2008-2011 Highlander Hybrid MHU48 brake-booster-pump branch; use the exact Toyota diag…
- Toyota 47070-48060 genuine brake-booster pump assembly
later pump/accumulator replacement after pressure-leak or pump diagnosis proves this assembly failed Fitment/availability: VIN-confirmed 2011-2013 Highlander Hybrid GVU48 brake-booster-pump branch within this record; production-date over…
- Toyota 44050-48320 genuine brake actuator assembly
ABS/regenerative brake actuator replacement only when actuator valves, electronics or internal hydraulic functions fail their specific tests Fitment/availability: VIN-confirmed 2008-2013 Highlander Hybrid MHU48/GVU48 actuator branch; do …
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (3)
Toyota T-SB-0130-19 and Customer Support Program ZKK apply to certain 2012-2014 Camry Hybrid vehicles with brake, ABS and/or TRAC warning lights or a Check VSC message. Verification requires C1391, C1252, C1256 or C1253. Toyota attributes the specified condition to a small internal brake-fluid leak in the brake-booster assembly with master cylinder. Warning lamps can have other causes, and the documents do not support extending this record to gasoline Camrys or other model years. ZKK's primary coverage ended March 31, 2021; its secondary coverage was 10 years or 150,000 miles from first use, so its published coverage period has expired for this model-year range as of 2026.
Common Symptoms
- Brake system warning light
- ABS warning light
- TRAC or slip warning indicator
- Check VSC message
How to Fix
Scan the Toyota brake-control system and confirm the exact DTC and VIN/application before repair. When T-SB-0130-19's condition is verified, Toyota's procedure replaces both the brake-booster assembly with master cylinder and the brake-booster pump assembly, followed by the specified initialization/bleeding and confirmation steps. Contact a Toyota dealer to confirm any current VIN-specific assistance, but do not assume ZKK remains active. Treat red brake warnings or changed braking response as safety-critical and do not buy campaign kits, used actuators, scan tools, or fluid from this card.
Owner tips & cautions
- WarningBrake, ABS, and TRAC lamps can have other causes. Verify C1391, C1252, C1256, or C1253 and the 2012-2014 Camry Hybrid application before authorizing the two-assembly repair.
- TipAsk Toyota to check the VIN and date of first use for any current assistance, but plan on ZKK's published 10-year/150,000-mile secondary coverage being expired as of 2026.
Sources for this issue (2)
The electro-hydraulic brake booster/accumulator assembly on third-generation Prius develops an internal fluid leak, so the accumulator can no longer hold pressure. The pump then runs constantly to keep pressure up (loud buzzing/grinding from under the driver's footwell) and eventually the system sets C1391 (often with C1252, C1253 or C1256), turns on the brake, ABS and hybrid warning lights, and falls back to unassisted braking with a hard, long pedal and much longer stopping distances. Toyota acknowledged the failure with Customer Support Program ZJB covering 2010-2015 Prius and Prius PHV brake booster and brake booster pump assemblies (10 years/150,000 miles; primary coverage has now expired).
Common Symptoms
- Continuous buzzing or grinding from the brake actuator, sometimes with the car off
- Hard, long brake pedal with little assist
- Brake, ABS, VSC and hybrid system warning lights on
- Longer stopping distances
- Brake fluid level dropping with no visible external leak
How to Fix
Diagnose with a scan tool that reads chassis codes; a running/buzzing pump with the car off and C1391 stored confirms an accumulator leak. The repair is replacement of the brake booster with accumulator pump assembly (frequently the pump assembly as well) followed by the Techstream-guided brake bleed/linear-solenoid initialization, which is required or the pedal will remain wrong. Check for remaining ZJB coverage or a goodwill claim first; used assemblies are a gamble because the same seals age on every unit.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota 47070-47060 brake-booster pump with accumulator
replace the diagnosed leaking/failed pump-accumulator branch before professional Techstream bleed and initialization Fitment/availability: 2010-2015 Prius liftback and 2012-2015 Prius Plug-in 2ZR-FXE; not the Prius v branch and VIN confi…
- Toyota 47070-12020 brake-booster pump with accumulator
replace the diagnosed Prius v pump-accumulator branch before professional Techstream bleed and initialization Fitment/availability: 2012-2017 Prius v 1.8L; use for the issue's 2012-2015 Prius v branch only and confirm VIN Fitment/availab…
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (3)
C1391 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does C1391 mean on a Toyota?
C1391 stands for "Abnormal Leak of Accumulator Pressure (manufacturer-specific)." C1391 is a manufacturer-specific brake code, documented mainly on Toyota and Lexus (often hybrid) models, indicating the brake control system detected an abnormal leak or loss of accumulator pressure in the hydraulic ABS/brake actuator. The accumulator stores pressurized brake fluid the system uses for power-assisted and ABS braking, and degraded internal seals can let it bleed down. Because this directly affects braking assist and can increase stopping distance, it is a serious fault that should be repaired promptly by a qualified shop. On Toyota it is documented across 4 models: 4Runner, Highlander, Camry, Prius.
What are the most common causes of C1391?
The most common causes of C1391 are: Failing brake booster / master cylinder accumulator seals, Worn or leaking brake actuator assembly, Internal hydraulic leak in the ABS/brake actuator, Low brake fluid level, Aged or contaminated brake fluid, Faulty pump or pressure sensor within the actuator, Faulty brake control (skid control) ECU. The specific cause varies by vehicle.
How much does it cost to fix C1391 on a Toyota?
Published repair estimates on Toyota range from $1,200 to $3,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for C1391 on a different make?
View C1391 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.