Brake Pedal to Brake Pedal Stroke Sensor Interaction Question

Does anyone here know how the Brake Pedal Stroke Sensor interacts with the actual physical Brake Pedal?

I am having trouble getting a new stroke sensor to calibrate and am wondering if there is an actual mechanical tolerance problem. I am following the installation instruction from TIS but am not getting the past step 2 as noted in:

INSTALL BRAKE PEDAL STROKE SENSOR ASSEMBLY

(a) When installing a new brake pedal stroke sensor:

(1) Install the sensor to the brake pedal support with the 2 bolts.

Torque: 9.3 N*m (95 kgf*cm, 82 in.*lbf)
NOTICE:
• Engage the sensor lever with the brake pedal groove.
• Check that there is no foreign matter attached to the sensor's contacting surface.​

(2) Strongly depress the brake pedal and break the sensor lever set pin.

*** This step does not break the sensor lever set pin ***​

(3) Remove the broken sensor lever set pin.
(4) Connect the sensor connector.​

​

 

No one here had an answer to my question so I answered it myself after doing a ton of research and hands on investigations.

There is a mechanical interaction between the Brake Pedal and the Brake Pedal Stroke Sensor in a working 2009 Prius. In the previous diagram, the tip of the stroke sensor does sit in the slot indicated.

What happened in my 2009 Prius was the bracket (into which the Brake Pedal Stroke Sensor bolts) got bent ever so slightly (not even visible to the human eye) during the removal process. This was just enough to cause the tip of the stroke sensor to fall short of the slot in the brake pedal clip. The resolution was to adjust the bent bracket so the stroke sensor properly aligned physically with the clip.

Attached are some pictures of the stoke sensor.



I also used the following trick to re-installing one whose “lever set pin” has already been broken and removed.

Take a simple tooth pick:

Cut about 1/3 the length off one end:

Use the 1/3 piece and insert it into the Stroke Sensor as shown:

 

Not sure why the stroke sensor images were dropped when the "post" button was clicked.

 

I must apologize for the delay in answering your question: “Any ideas on why the sensor failed?”.

While it is a simple question, the answer is far more complex. In fact, it is my belief that the sensor did not fail. I can probably figure out a test scenario that will show that the sensor I replaced is in fact still good.

I don’t know if this will help others, but it might, so I will lay out the rather lengthy background and identify what I truly think “fixed” my Prius. The up side to this is that my 2009 Prius is working as it should. I did get it completely working this past Monday (2018.03.12).

Around 2017.12.10 I took my 2009 Prius to the Toyota dealership to get an estimate on what it would take to fix the air conditioning. I had been working with them for several months to identify where the coolant was leaking. After refilling the coolant and adding a dye, they felt the evaporator was where the coolant was leaking from the system. They quoted me $2700 to fix the problem. That seemed rather expensive. Quite frankly, it was more than ½ the value of the car so it made little economic sense to agree to that price. I did check with other dealerships and they were in the same ballpark.

At the time, I had more free time than I had money to spend so I looked into what it would take me to do the work. The cost of Toyota parts to replace the evaporator was less than $700 so I decided to do the work myself. It does take 1 special tool to disconnect the feed and return tubing containing the coolant from the evaporator. There are two variants of this tool (which is very confusing to the uninitiated) with a rather dramatic cost differences as well as appearance differences. The cheaper of the two variants is what I used.

For those that don’t know why the Toyota cost is so high, it is the labor to basically remove the entire dashboard (minus a few items) as well as to remove the windshield wipers and containing structure under the hood (as well as putting all that back together). It seems that many vehicle manufacturers have opted for the “lowest cost” vehicle assembly process, which sacrifices the ease of repair in lieu of low cost assembly. The evaporator is assembled into a subassembly, which is put in the car in the early stages of the vehicle assembly. Almost everything else is assembled around this, henceforth the need to remove so much to replace the evaporator.


View from the passenger side with the sub assembly containing the evaporator removed.


View from the driver side with the sub assembly containing the evaporator removed.

It took less that week to perform all the work of disassembly, replacing the evaporator and other essential AC related components as recommended by Toyota TIS documentation, and then reassembling the vehicle. This included some wait time for the special tool to arrive.

It was after reassembling the vehicle that I got the “Brake Control”, “Brake”, “ABS”, and “VSC” warning lights on the dash.



I rechecked all the connections and could not find anything that wasn’t connected properly. I did take it to my local Toyota dealership and had them diagnose the problem. The local Toyota dealership came up with two DTC’s C1247 and C1392 from the brake control subsystem and told me I needed to have them replace the Skid Control ECU as a cost of $2000.

I had a hard time believing that anything was done that should have caused the Skid Control ECU to go bad. I wasn’t willing to let the dealership perform this work and decided it was time to invest in some diagnostic tools. I bought a VCX Nano from VXDiag with a copy of Toyota Techstream. I spent a ton of time reading and searching Prius chat for other people’s experience.

The dealership had quoted a cost for the Skid Control ECU of $1500. The least expensive “new’ unit I could find was $1325. I did invest in access to TIS. My past experience was telling me that nothing in the electrical components could have gone bad and that I should focus on the wiring harness for something that may have come loose there. I did let the recommendations from the dealership influence me so I bought my first used Skid Control ECU. I put it in. I performed all the steps documented in TIS and still came up with the same DTC’s as the original Skid Control ECU. I went through the detailed diagnostics steps in TIS (specifically Doc ID RM000001S1A004X). In Step 5 I was getting 4.42 Volts across connector S9-6 (VCSK) and connector S9-8 (SKG). I could not get the indicated voltages for Step 6 on the Brake Pedal Stroke Sensor 1 or Brake Pedal Stroke Sensor 2. Both were showing the same 0.7 volts. None of the voltages in step 6 part e could be attained. This is where I made the choice to buy a new Brake Pedal Sensor.

It was during the installation of the new Brake Pedal Sensor that I initiated my question in Prius Chat.

Turns out that I got the same results with the new Brake Pedal Sensor that I got with the original sensor (and why I’m willing to bet the original one is still good).

Again, I let the dealership’s recommendation influence me so I ordered a second used Skid Control ECU. (I now have 3 Skid Control ECU’s and 2 Brake Pedal Stroke Sensors.)

After putting the third Skid ControlECU in, and redoing the initializations, I got the same exact DTC’s. This finally convinced me the electronic parts were not bad at all and the problem had to lie in the wiring harness or in a connection. I started checking each and every connection beginning with the Skid Control ECU connectors. I was seeing some connectors that weren’t getting the documented values. These appeared to be related to the Brake Pedal Stroke Sensor.

I decided to double check the sensor. I removed it and reinstalled it. I noticed that simply loosening and tightening the bolts for the sensor was enough to cause the pin to improperly disconnect from its “groove”. I was able to wrap my right hand around the pedal and could squeeze the bracket with enough force to bend it back into place so the pin could lie in its groove properly.

During this process, the Brake Pedal Stroke Sensor connector popped off. After reconnecting it and loosening the bolts so it could be adjusted to reflect the required voltages for Brake Pedal Stroke Sensor 1 and Brake Pedal Stroke Sensor 2, I hooked up Techstream once more. This time I was able to see different voltages on Brake Pedal Stroke Sensor 1 and Brake Pedal Stroke Sensor 2. I was able to bring them into the range required (0.8 volts on Brake Pedal Stroke Sensor 1 and 4.2 volts on Brake Pedal Stroke Sensor 2).

This told me that either:
1. I did not have the connector on the Brake Pedal Stroke Sensor seated properly or
2. The wires in the harness which I had to put pressure on to loosen/tighten the top bolt re-seated loose connections.

Either way, the DTC’s went away after initializing and the car is working as expected. I have not been willing to replace the original parts and retest to prove my belief that my original parts are still good.

Hope this helps other.