2010 brake system

Part of problem diagnosis is to understanding the system so we can map symptoms to potential failure modes. The poll associated with this posting is to ask about subtle items that may or may not have any bearing on the brake anomolies. These are just hypothetical mappings but an important step. One of the best source are Toyota's New Car Features:

• BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: BRAKE CONTROL SYSTEM: DETAILS (2010 Prius), Doc ID: RM000004221000X
• BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: BRAKE CONTROL SYSTEM: GENERAL (2010 Prius), Doc ID: RM00000421Y000X

This is just a brief summary of the details.

OVERVIEW

The Prius brake system is an integrated system that balances regenerative braking, hydraulic braking, traction control, antilock skid control, and balance into a simple to operate system:


Now one of the symptoms reported is an extended 'loss of braking force.' Considering the curve above, it is likely this is a hydraulic system release. Given the time-scale, this chart suggests the effect occurs in an early braking condition versus a longer, braking interval when regenerative braking force might be a higher percentage.

It is a fairly sophisticated system that also adjust braking force based upon the vehicle loading:


So one question is whether or not the vehicles experiencing the braking symptoms may have or not had a load in the rear.

SIGNIFICANT ELEMENTS

	Column 1	Column 2
0	[th]Assembly[th]Part[th]descriptions
1	[tr][td]Master Assembly[td]Brake Actuator[td] 4 switching solenoid valves
2	[tr][td] [td]Brake Actuator[td]2 linear solenoid valves
3	[tr][td] [td]Brake Actuator[td]8 control solenoid values
4	[tr][td] [td]Stroke Simulator[td]generates pedal stroke per driver's input
5	[tr][td]Skid Control ECU[td] [td]manages system
6	[tr][td]Stroke sensor[td] [td]detects brake pedal operation	analog
7	[tr][td]Speed sensors[td] [td]one for each wheel
8	[tr][td]Power ECU[td] [td]responds to regen request from skid control ECU
9	[tr][td]Power ECU[td] [td]sends regen value to skid control ECU
10	[tr][td]Power ECU[td] [td]controls motive force per skid control ECU
11	[tr][td]Elect. Brake Dist.[td] [td]adjusts front and rear and left/right braking
12	[tr][td]Stroke sensor[td] [td]contact type variable resistor	stroke position
13	[tr][td]yaw rate sensor[td] [td]left and right acceleration
14	[tr][td]acceleration sensor[td] [td] forward and backward acceleration

Of these elements, I tend to wonder about these sensors:

• brake stroke - there is history of wiper-based, sensors being a little weak. It is one reason Hall effector sensors are used more commonly.
• acceleration sensor - something we'll measure with the USB sensor.

Thanks to the help from those who have experienced the problem, we have a growing list of surface conditions that seem to trigger the symptom:

http://hiwaay.net/~bzwilson/prius/Prius_bump_010.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_020.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_030.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_040.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_050.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_060.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_070.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_080.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_090.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_100.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_110.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_120.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_130.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_140.jpg​

http://hiwaay.net/~bzwilson/prius/Prius_bump_150.jpg​

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You can help by posting photos or Google Street view or Google map addresses of the places this happens. The key to diagnosis will be finding a way to replicate the problem at will. Then we can do things like:

1. swap Prius - if one vehicle always has the problem and another does not, it means finding out what is different between the two
2. quantify the problem - we need engineering units that document time, duration and magnitude

Bob Wilson

 

I'm really interested in the slow-speed, stopping anomalies as these are often close to other objects (aka., bumpers, walls, curbs, walkways.) Also, understand I'm using the "New Car Features," NM1291U, and the "2010 Maintenance Manual," EM1291U, as my source materials. I'm not a Toyota trained technician and my reading and interpretation is likely to have unintended errors. But this is my best understanding ... today ... and I appreciate corrective posts so we can all advance our knowledge and understanding.

BACKGROUND

A non-error code, braking anomaly has been reported by some 2010 Prius Chat members:

• ~18% report "scary, safety issue" (18)
• ~41% report occurs (40)
• ~59% report not experienced it (57)

It seems to be a low speed phenomena:

• ~47% report speeds 20 mph and slower

Typical report:

Modest braking that passes over a manhole cover, railroad crossing, patched surface, or pothole that leads to a longer period of reduced braking.
​

Survey From Maintenance Manual

System architecture:


These are bits that suggest interesting aspects that may apply to our braking system:

"Do not remove or install electronically controlled brake system parts such as the steering angle sensor, yaw rate and acceleration sensor or brake pedal stroke sensor except when required, as they cannot be adjusted correctly after removal or installation." (BC-1)

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I'm still reading the brake section, over 300 pages. But I wanted to start the conversation. More details to follow.

Bob Wilson

 

You could help by giving us a Google address of the speed bump. If there is not Google Street view, take a photo and post it here ... with a yard stick or scale so we can understand the shape. But a simple "me too" post without technical details or even a photo ... wastes everyone's time:

• ours because we already know something is going on
• yours because you already knew something was going on

Please, provide additional technical details and be part of the solution.

Bob Wilson

 

I'm still reading the maintenance manual description of the brake system and found these gems:

• "After replacing any VSC related componets or performing front wheel alignment adjustment, clear and read sensor calibration data." BC-19 - there is a fairly extensive calibration process that covers all of the input sensors. It may require a service order to make sure this procedure is done but given the number of steps, the labor won't be cheap.
• "If there are no DTCs but the problem still occurs, check the circuit for each problem symptom in the order given in the table below and proceed to the relevant troubleshooting page." BC-32 - Nothing like the symptoms reported show up in the table. However it outlines a significant number of steps including my favorite, checking the connectors.
• FREEZE FRAME DATA BC-42 - saving the data occurs only when a code is stored. I would not expect anything useful here unless a code is shown.
• DATA LIST BC-46 - lists the signals that the 'Techstream' can read. This would be great data if recorded during an event. Many sources are dual such as stroke sensor, yaw and accelerometer data.
• "FR Regenerative Request | 0 Nm to 65536 Nm | Changes according to brake pedal force (When depressing the brake pedal lightly after above 30 km/h (19 mph) or more avoiding sudden braking.)" BC-49 - sound familiar?
• ACTIVE TEST BC-50 - a way to exercise the braking system components in the bay.

The rest of the sections cover parts replacement.

Bob Wilson

 

You can help be part of the solution by providing a street address of this bump ... something we can use Google Map and Google Street View to see what it looks like. Otherwise, it is just another "me too" posting with no contribution to the diagnosis.

Bob Wilson

 

So looking at the technical content of your posting:

Have I properly quoted how much technical content was in the posting? OVer in the main forum are several brake threads and that is an excellent place to vent your spleen.

Provide facts and data such as a location that you've experienced the problem; specific configuration; or something of value. Otherwise, I might as well <PLOINK> your username.

Either be part of the solution or remain part of the problem ... noise distracting us from hard, engineering data.

Bob Wilson

ps. The <PLOINK> refers to our ability to add folks to the "ignore list" under UserCP. Sometimes, you just have to 'turn up the squelch' to concentrate so serious postings show up. My general rule, three strikes and 'your out.' ... As my drill instructor said, "Don't get mad, get even."