Update: To see all of TTAC’s related articles on the subject of Toyota gas pedals, go here:
In yesterday’s post , we offered a bounty for anyone to open up both the CTS (bottom) and Denso (top) Toyota gas pedal assemblies. No one took us up, and no one anywhere else has done it, so we took it upon ourselves . Here they are, both e-pedal assemblies taken apart and examined, in our quest to understand if and what the significant differences are, and how Toyota’s possible “shim” fix would work. On initial observation, it appears that the CTS may be perceived as being the more solidly engineered/built unit, in that the pedal pivots on a traditional and solid steel axle whose bearings are brass or bronze sleeves. The Denso’s whole pivot and bearing surfaces are relatively flimsy-feeling plastic. But that can be deceptive, and we’re not qualified to judge properly if it is indeed inferior or superior. So the question that goes beyond the analysis of these e-pedals is this: are these units really the full source of the problem, or are they scape goats for an electronics and/or software glitch? Pictures and tear down examination and analysis follows:
Update #2: It’s clear to me now that the CTS unit I took apart already had the side cover plates (sheet metal) removed before I examined it. One can see where they fit, and are obviously intended to protect the exposed axle pivot and bushing seen above and below:
Lets take a close look at the CTS unit:
We drove out the pivot pin with a C-clamp and screwdriver. It’s a very traditional design, like millions of plain-bearing (non roller-ball bearing) non-lubricated devices used in a huge variety of devices for decades, if not even centuries. The softer brass or bronze acts as relatively low-friction bearing. With the substantial pressure from the springs, it seems relatively unlikely that this would lock up, but that seems to be the concern. It’s possible that there is a greater potential for binding due to the tighter tolerances in the axle/sleeve assembly. A close up of the axle and bearing:
A big question for us was if there are dual springs, in the case one fails. Here is the CTS unit apart. Note that the pointed metallic part on the bottom of the pivot is the magnet that passes between the sensors in the case of the unit, which is how the sensor sends the throttle position signal to the engine controller.
The outer red spring surrounds the inner black coil spring. It seems that the possible “shim fix” that Toyota is considering would be a spacer on the bottom of this spring assembly, which would increase the pressure on it and presumably reduce the likelihood of the pedal sticking. I’m not an expert on springs, but the spring is already pre-loaded (compressed) to some degree when it is assembled, and unless these are variable rate springs, I wonder whether that would actually increase the working resistance of the spring unit. Since I had no problem taking the pedal/pivot unit apart which also houses the spring unit, and reassembling it as well, it would appear that if that route is taken, it should be easily done in a few minutes at the dealership.
To understand that part more clearly, here is a shot of the CTS unit assembled, with the main cover off, showing the pivot arm with the magnet and how it passes past the sensors (Autoblog has a video explaining how the CTS sensor works, but no teardown):
Lets examine the Japanese Denso unit (below, which comes apart by removing the side cover held on by five screws. It is already apparent from the outside that there is no axle pivot that runs through this unit.
The Denso is a dramatically differently designed unit. The pivoting unit (green) is a plastic “bearing” that just sits inside the two outer units. One can see what it bears against in the side cover. The magnet is the square unit in the middle of the green pivot, and the sensor appears to be the round unit inside the side cover. The numerous small bright metal protrusions on the side cover are not identified. I thought they were the sensors, but nothing runs over/past them. Here is a closer look at the spring assembly still installed and the plastic pivot “bearing” surface:
Here’s another view of the Denso unit:
The Denso spring unit, also a double coil unit, has a protective “sleeve” over the inner spring to reduce binding between them, since the Denso unit’s spring is in a substantially curved position inside the housing. The CTS does not have this feature, but it appears that its spring is less curved when installed.:
Subjective impressions of taking these two units apart are the opposite of what one typically would assume. The Denso unit feels “cheaper” in that the whole pivot bearing area is all plastic, and feels relatively more flimsy (that doesn’t necessarily mean it actually is). The CTS unit relies on very traditional steel and brass sleeve bearing that took some effort to take apart. The CTS pedal has no play or wiggle when assembled.
The big question is why Toyota completely redesigned the CTS unit from the older Denso unit. Perhaps they were actually trying to design a sturdier assembly because the Denso unit was in question. Perhaps the Denso unit is actually inferior in certain ways, but Toyota didn’t want to pay for new tooling to bring the Denso unit up to the newer CTS design? Source have told me that the Denso unit is likely to be recalled shortly, and the LA Times is reporting that there are known claims of pedal issues with the Japanese Denso unit.
From our perspective, it seems possible but rather highly unlikely that condensation is somehow causing the very solid CTS bearing pivot to lock up, given the spring tension and the units solidity. CTS claims it has only experienced a very limited degree of stiction at or near the idle point on a very few examples.
A key question is which unit was designed first. The CTS unit was used in Avalons since ’05 MY. Apparently Denso units have been in use before that. The question being: why did Toyota design two such fundamentally different units, and is the latter one designed to address any deficiencies of the older one?
Both units are surprisingly simple and obviously cheap, yet they feel robust when assembled. I believe Toyota has stated that the unit cost is $15 per pedal assembly. The retail price is about $120.
The overriding question is if these pedals are really the predominant or sole cause in any true (non-floor-mat caused) unintended acceleration, or whether electronics are the real 800 lb gremlin in this whole affair. Toyota has not acknowledged that…yet.