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Car Jiggles After 30 Sec At Stoplight

yrwei52

2016 Mazda CX-5 GT AWD w/Tech Pkg
Contributor
:
Plano, Texas, USA
Torque convertors do not lock up at low speeds, and definitely not at anything approaching a stop. Historically this was limited to top gear and vehicle speeds above 35-40mph, but with more advanced computer controls, has expanded to engaging in multiple higher gears with lots of additional parameters such as fluid temperature, throttle position, etc. involved in the logic. But definitely no logic would have a torque convertor locking up at low speed or a stop.
Mazda’s SkyActiv-Drive 6-speed automatic transmission uses multi-plate lock-up clutch in every gear to transmit power directly at the speed over 5 mph. Toyota’s Direct Shift 8-speed automatic transmission is doing the same.
 
Mazda’s SkyActiv-Drive 6-speed automatic transmission uses multi-plate lock-up clutch in every gear to transmit power directly at the speed over 5 mph. Toyota’s Direct Shift 8-speed automatic transmission is doing the same.
So 5mph is a stop? Didn’t think so…. So once again, since the topic of this discussion is something occurring at a complete stop, this transmission lock up converter discussion is not relevant.
 

AVC

:
'17 CX-5 Select
From my observations it has nothing to do with the transmission (it's sitting stationary in 1st gear), but rather with PCM programming re: the A/C compressor operation.

As to why a 2016 wouldn't do this, I'm guessing while the base PCM code for Skyactive is the same from 2012 to current, there have been numerous tweaks along the way, and certainly can believe at the 2017 MY when they were tweaking NVH from previous generation. If the same A/C compressor strategy routine is present for 2017 and newer NA or Turbo, then the behavior would be the same. As the bump doesn't happen at *every* compressor cycle, it would appear to be a minor software bug/race condition under some situations; i.e. maybe the PCM is fussing with emission monitors, or timing a canister purge or something else when the HVAC interrupts it for an event. Agree only the software architect would know.
 
From my observations it has nothing to do with the transmission (it's sitting stationary in 1st gear), but rather with PCM programming re: the A/C compressor operation.

As to why a 2016 wouldn't do this, I'm guessing while the base PCM code for Skyactive is the same from 2012 to current, there have been numerous tweaks along the way, and certainly can believe at the 2017 MY when they were tweaking NVH from previous generation. If the same A/C compressor strategy routine is present for 2017 and newer NA or Turbo, then the behavior would be the same. As the bump doesn't happen at *every* compressor cycle, it would appear to be a minor software bug/race condition under some situations; i.e. maybe the PCM is fussing with emission monitors, or timing a canister purge or something else when the HVAC interrupts it for an event. Agree only the software architect would know.
And there in lies the issue. As with most every complex software system, individual tasks and modules are assigned to different individuals/teams and then all put together into a final system. A good contingent of developers don’t take the time or out in the effort to actually understand what the end product actually is or how small nuances in coding impact whether to code “works” or is actually well designed for the application. Also, the higher level staff responsible for the integration of all the pieces of code rarely do a detailed review and testing of how it all interacts. They test specific required functionality and if there aren’t obvious major issues, it all gets pushed forward to stick to the schedule. It’s rare that a cohesive team that really cares about the end product all work together during the full development process to create a great result. All of the additional capabilities and better technology allow the software architects to create a wonderful vision for having so many things controlled and adjusted all the time. But they don’t seem to allocate enough time and resources to the final testing and adjustment phase to eliminate this type of bug. Everything still works, and most end users don’t pay close enough attention to notice or care, so onward it goes to production.

Same across so many industries, companies, etc.