Brake pedal vibration on startup

My first guess would be the brake accumulator pump, or whatever you care to call the electric boost pump for the power brakes.

Tom

 

Perhaps its the pump that gives feedback to the brake pedal cylinder (if there is one, as I may be making parts up)?

 

A very interesting problem. Since the service manager experienced the vibration himself, hopefully he acknowledges this is a real problem. Has the problem been escalated to Toyota GB for help?

I took a look at the diagnostics section of the repair manual, studying the schematic diagram that shows how the various brake parts relate to each other, trying to figure out how pressure from the brake pressure accumulator pump might be transmitted back through the brake master cylinder so that you would feel vibration in the brake pedal. There are two "master cut" solenoids that control flow of brake fluid from the brake master cylinder. Maybe one of those solenoids is open momentarily when you are starting up, which allows you to feel the vibration.

DTC C1315 or DTC C1316 are supposed to be triggered if there is a problem with these parts; but since the problem is intermittent, maybe the diagnostics are not sensitive enough to trigger.

If a solenoid is the problem, the fix would be to replace the brake actuator assembly that contains the various solenoids. I am very interested to hear what the resolution to your problem is.

 

Yes, please attach your photo. Note that attaching a file is a choice within "Additional Options", while you are composing your reply.

 

Sorry, I can't identify the warning lights in your photo besides the master warning light (red triangle) and the air bag light. Since the air bag system is unrelated to the braking system, I am wondering if your problem is just a bad 12V auxiliary battery. Have you replaced the original equipment battery yet; if not maybe this would be a good idea.

Can you please identify the other warning lights that came on and list them?

 

Thanks. It appears that the air bag light is just coming on & off as normal, upon startup.

If you have a digital multimeter, you might try measuring the voltage across the 12V auxiliary battery after the car has been IG-OFF for 30 min. or so. If the voltage is less than 12.6V it is not fully-charged, and the lower the reading the worse-off the battery is.

I haven't seen a problem similar to yours before, so I can't say that replacing the battery will help. However it won't hurt, your current battery is 4 years old, and when Prius electronics act weird, the battery is one of the first trouble areas to consider.

Did your dealer offer advice besides waiting for the problem to get worse so that the tech can retrieve a DTC?

 

Battery is in right rear corner, open lift back lift floor then a panel in the right side of the floor lifts out, The battery is right there.

 

Suggest you consult the terms and conditions of your extended warranty, but it is not likely that the 12V auxiliary battery would be included.

In the US the going dealer price is ~US$160.

 

In case the resolution wasn’t clear, I had the same issue, and it was a result of a bad 12 V battery. Because it was struggling to maintain voltage during the startup sequence, various checks were failing, hence the lights on the dash. One of those steps must be the brake controller that happens to reside right next to the battery and was likely an underlying cause of the vibration felt in the pedal.