Brake switch failure, no start, no brake lights

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.

 

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.

 

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!

 

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.