Some 2011-2015 Toyota Prius and 2012-2015 Prius Plug-in Hybrid vehicles may exhibit a condition where the brake,  anti-lock brake system (ABS) and/or active traction control (TRAC) warning lights are on and/or a check vehicle stability control (VSC) message displays. Diagnostic trouble codes (DTCs) C1391, C1252 and C1253 may be stored. This condition may be caused by a small internal brake fluid leak inside the brake booster assembly with the master cylinder.

Are the brake, ABS and/or TRAC warning lights on and/or does a check VSC message appear on the display? If yes, continue to Step 2.

Using Techstream, check and record any DTCs. If the afore-mentioned codes are set, continue to Step 3.

Remove the brake booster assembly with the master cylinder.

Remove the brake booster pump assembly.

Install a new brake booster assembly with the master cylinder.

Install a new brake booster pump assembly.

Test drive to confirm the repair.