What does code C1391 mean?

C1391: Abnormal Leak in Brake Accumulator (Toyota)

Severity: high

What it means: Toyota's skid control system has detected that the brake accumulator is losing pressure abnormally. Toyota's bulletins link it to a small internal brake fluid leak.

Safe to drive? Use caution. The car usually still brakes, but pedal feel and stopping distance can change. Get it checked promptly, and stop driving if the pedal feels soft or travels further than usual.

Common symptoms

Brake, ABS and/or TRAC warning lights
Check VSC message
Brake pump running longer or louder than usual
Change in brake pedal feel

Likely causes, ranked

Small internal fluid leak in the brake booster assembly with master cylinderShop
Worn brake booster pump or accumulatorShop
Internal leak in the brake actuator (some models)Shop
Pump relay or wiring faultShop

Vehicle-specific notes

What it means: Toyota's skid control system has detected that the brake accumulator is losing pressure abnormally. Toyota's bulletins link it to a small internal brake fluid leak.

Severity: High. Safe to drive? Use caution. The car usually still brakes, but pedal feel and stopping distance can change. Get it checked promptly, and stop driving if the pedal feels soft or travels further than usual.

DIY or shop?

Dealer. Toyota replaces the brake booster and pump assemblies together.

Vehicle notes

Toyota covers verified failures with these codes on certain hybrids, including 2013–2015 Avalon Hybrid, under customer support programs. Check your VIN with a dealer.

Before you replace parts

Read all stored codes, including detail (INF) codes on Toyota hybrids.
Check your VIN for recalls, service bulletins and extended coverage.
Clear the code only after a repair, then confirm it stays off.

Safety / mechanic note

Verify with a mechanic. Brake system faults affect stopping. A code points to a circuit or system, not always a specific part.