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Brake switch failure, no start, no brake lights

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by jengel, Oct 30, 2013.

  1. jengel

    jengel Junior Member

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    Not sure how common this is, but our 2007 Package 4 Prius (70k miles) recently started exhibiting a no start condition that was quite annoying. It could be corrected by pumping the brakes vigorously, which of course suggested that the brake switch on the brake pedal was malfunctioning. Observation of the brake lights confirmed that the no start condition was coincident with no illumination of the brake lights. 30 minutes, some cursing, and $50 got me a new switch installed which solved the problem.

    My concern is that I observed that after the car was successfully started, the brake lights would continue to be intermittent, which is a major safety problem. I made a report to NHSTA (File a Safety Complaint | Safercar.gov | NHTSA ) and would suggest that other owners experiencing the problem do the same.

    Tearing apart the old bad brake switch shows that it is a design or manufacturing issue with arcing, contamination, or material incompatibility (galvanic corrosion e.g.) causing a fouling of the sliding switch contacts preventing reliable low-impedance switching. This is a serious issue that should be corrected. As the Gen II prius's out there on the road get ollder this problem will only become more prevalent and dangerous. The sooner enough complaints are made, the sooner action is taken to correct the issue.

    I'll take some pics of the bad switch and post.
     
  2. jengel

    jengel Junior Member

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    Took some pics, not great quality, but you can get the idea. The sliding contact fingers (second image) appear to have a silver-ish plating on the contact side while the backside of the fingers appears to be natural phosphor bronze. Since the stationary contact pads (first image) in the switch housing that the fingers slide onto and make contact with appear to be bare copper it puzzles me why they would plate the fingers with something else. From the pics you can see the dark track marks on the housing contact pads which represent some kind of fouling that likely interrupts electrical contact. The fouling shown is what remained after I attempted to clean the fouling and fix the issue. I attempted to clean with standard non-CFC brake cleaner which is a magic mix of high VOC solvents that removes a lot of residues. So my guess is that the fouling is something more like an oxidation product of the plating on the movable fingers rather than some hydrocarbon residue. Discoloration of the plastic housing can also be seen where the fingers slide on the white plastic. A close up look at the finger tips (second image) shows that at the point of contact the silver-ish plating is worn away exposing the bronze underneath.

    In any event, I think the switch should have lasted far more than 70k miles and considering that brake switches are old tech I would expect it to last the life of the car as they have on every other car I have owned or heard talk of. Given the criticality of the brake switch to the successful and safe operation of the Prius, this kind of design failure is baffling.

    contact_tracks.jpg contact_slider.jpg
     
  3. nh7o

    nh7o Off grid since 1980

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    Note that the brakes in the Prii are still mostly functional even without that switch working, so it may not be all that unsafe. The stroke sensor still engages, and the mechanical connection is always there.

    The vast majority of Prii on the road do not see this failure after many more miles, so I would say that the switch is probably of reasonably standard construction and nothing unusual. But that means there will always be outliers. Statistics being what they are, in a consumer situation some people will just end up with an early failure of something or other. Consistency of manufacture is a difficult thing to come by economically. Mil spec parts are pricey.
     
  4. jengel

    jengel Junior Member

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    Less than 1.2 million Gen 2 Prii were sold worldwide (Toyota Prius - Wikipedia, the free encyclopedia). Based on my reading on PriusChat (PC), I'd say around 5 PC readers have experienced this problem and posted about it. If we assume 5% of Prii owners worldwide read and post on PC, then this is roughly a 100ppm (1 in 10,000) problem. 100ppm is not a large number, but for a critical to function and safety issue it is quite large in my opinion. Especially considering the cost of the part (<$50 retail). My guess is it is a material incompatibility issue which could likely have been prevented with an extra $2 of gold plating. The cost of a recall for putting that new switch into 1.2 million Prii, now that is the kicker. If only 1% of those 100ppm Prii are rear-ended due to faulty brake lights... well I don't have any actuarial tables in front of me, but I guess I shouldn't hold my breath for a recall.

    There was a recall on brake switches for the Gen 1 and early Gen 2 Prii (Brake light recall | PriusChat) however, so hope springs eternal.

    Thanks for the reply!
     
  5. nh7o

    nh7o Off grid since 1980

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    OK, didn't know about the recall on the switches. I would say that PriusChat statistics are a bit skewed, in that those with problems are much more likely to post than are those without problems. That said, I wonder about this particular failure in actual practice. It seems that people are able eventually to get the car going by pressing the brakes repeatedly, as you did. At that point the switch is working again, and continues to do so until the next start, when it goes flakey again.

    I have not seen any reports of people getting rear ended because of no brake lights. Perhaps someone else has?
     
  6. jengel

    jengel Junior Member

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    Let me clarify. If you pump your brakes 5 times before you can get the Prius to start, the switch will continue that level of intermittency during operation. Meaning that your brake lights may only illuminate 20% of the time, or less. The flakey-ness is not solved by starting the car. The switch being intermittent will not prevent the car from operating when it is running only prevents the brake lights from lighting up. Also, anecdotally, I noticed some odd brake grab, increased fabled "acceleration" and other transient behavior when the switch was flakey which I think could be due to the skid computer not getting the memo that the brakes are being applied. Might also impact the handoff between regen and friction braking. All such symptoms disappeared when the switch was replaced.
     
  7. Skittles69

    Skittles69 New Member

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    My car turns on but won’t register the breaks so you can’t put it into any gears or nothing.