Within the past month in Ohio, the weather has gone for weeks of below freezing to below 0 fahrenheit. Currently, it is 45 with the last few days being 50-60. Some symptoms about my 350K 2007 Prius: 1. Loud beep at startup approx 10seconds 2. BRAKE light on dash far left light near door 3. Intermittently no brake pressure...ie soft brakes 4. NO CODES via Autel Toyota OBD (brake related) Watched several videos about possible causes, brake actuator being the primarily mentioned issue. However, there is no noise from the brakes (whirring sound) but sometimes there are a few clicks from that area where the BA is. Car seems to run fine otherwise. My feeling is that the sudden-change in warming temperature caused some expansion on the BA and maybe the issue might be the lines going into the BA are looser or something to do with brake not being distributed evenly. I checked the brake-fluid and its OK. I understand that 350K is a lotta miles and its probably the BA but I'd like to exhaust other possibilities before undertaking this job. As a sidenote, I'm semi-experienced with mechanical-work but how involved in time & effort would it be to do a replacement, I'm more worried about the install not being 100% tight and still having this issue. At some point we all gotta let these things out to pasture so I'm kinda on the fence. Thanks for any advice.
You should hear the whirring sound even on a good actuator. First when you open the driver door, and every so often when applying the brakes. First thing to check in cold weather is the 12v. Get a free load test at most auto parts stores
thanks. I'm gonna put the 12v on the charger today then. just curious, how the 12V plays a role in the brake actuator so i asked GROK AI. the answer: does 12v battery in 2007 prius affect brakes Yes, a weak, low, or failing 12V battery in a 2007 Toyota Prius (second-generation model) can affect the brakes — but usually not by making them completely fail or lose all stopping power. Instead, it often triggers warning lights and related issues. The 2007 Prius uses an electro-hydraulic brake system (with a brake actuator) that relies heavily on the 12V auxiliary battery to power the electronics, computers, sensors, and the brake system's control modules. The high-voltage hybrid battery handles regenerative braking and propulsion, but the 12V battery is crucial for overall vehicle electronics, including brake-related systems.Common effects from a low or dying 12V battery include: Brake warning light, ABS light, and/or VSC (Vehicle Stability Control) light illuminating on the dash. Brake system entering a fault mode or fail-safe, which can cause a harder brake pedal feel, reduced assist, or messages like "Check braking system" or "Apply parking brake" prompts. In some cases, the brakes feel "spongy," only the rear brakes seem to work properly, or there's unusual behavior when pressing the pedal (e.g., during startup or while driving). These issues often appear when the 12V voltage drops too low (e.g., below ~10.5–11V), causing erratic sensor readings or module errors. Many Prius owners report that replacing a weak 12V battery clears these brake/ABS/VSC lights and resolves related symptoms, as low voltage causes "ghost" codes or temporary faults in the brake actuator system. It's a common first troubleshooting step before assuming a more expensive issue like a failed brake actuator (which is a known problem on Gen 2 Priuses but typically shows different symptoms, like constant pump cycling noises). If your 12V battery is old (they usually last 3–6 years), low on charge, or failing, it's worth testing/replacing it first — auto parts stores often do free load tests. If the lights persist after a good battery and reset (sometimes by driving or using a scan tool), then scan for codes or check brake fluid/sensors/actuator.If you're experiencing specific symptoms (e.g., lights on, hard pedal, no braking power), describe them for more targeted advice! Always prioritize safety — if brakes feel compromised, don't drive until checked.
