I have the same symptoms happen to me especially in stop and go situations and where traffic is constantly moving between 5 and 0 mph. I never associated it with an issue, since the braking system on the spark is different from conventional setups.nozferatu wrote:Hey Skullbearer,Skullbearer wrote:Definitely not a normal sound or feel, but it probably is related to the blended braking system.
You can replicate the 'correct' sound of this change by using moderate regen braking at speed (say 45mph) and then shifting to N. The vehicle makes a very slightly clunky transition to 100% hydraulic brakes, but has almost identical feel after transition. The sound and feel are not nearly so severe that they would cause alarm, and everyone should do it at least a couple of times to know what's 'normal' (I did it on accident the first time). Blended braking is a very difficult process to manage, both mechanically and software wise, so I think Chevy did a fantastic job with it so far. The vehicle makes the transition gradually from some set speed during normal continuous braking... usually from around 6mph down to 2 or 3 mph. Reliable and efficient torque control in a PMAC motor begins to become very difficult at very low speeds and can cause a jerky braking feel, so the transition to hydraulic braking keeps it smooth. On your problem it either has to be a bad controller, bad electrical connection, or most likely a bad blended braking system (the electro-mechanical portion, which may be a solenoid or other proportional valve inline with the master cylinder output, or even the master cylinder itself). I don't know what unit Chevy used, but Bosch recently began selling a production blended braking unit that acts as the master cylinder and provides the same feel as if you are actually braking, but controls the actual pressure output to the brake system. The Bosch unit is the only 'off-the-shelf' system that could do the blended braking style that the Spark has, so I'll be it's what we'll find in our vehicles. Given that it's a very new product, we should all keep an eye out for failures... worst case though, the system 'should' fault to an open bypass state... ie 100% hydraulic brakes.
If your dealer is having trouble diagnosing it, they should start by checking the wiring harness to the blended brake unit, then replacing the unit itself, and finally with a controller replacement. If it starts happening above 6mph, pay attention to whether or not the electric power meter suddenly goes to no regen even though you're braking, it could be falsely detecting an N position on the shifter.
Thanks for the input. It's a bit disconcerting that the dealership has only ONE certified tech on hand for the Spark EV..which makes me concerned to be honest. But I hope it's an easy fix and they don't have to tear the car apart.
I also get the sense that it may be a bad electrical connection because as I said earlier, I hear a faint but definite variable pitch electrical "circuit" type sound emanating from the front wheel arches/areas...while in P or N.
I've actually forwarded this posting you wrote above to the shop foreman as I think it's a great starting point for them.
My problem is definitely most noticeable at low speeds...5 MPH and below...with perhaps coming to a stop or in N or P allowing the problem to be most noticeable. It's quite loud...the twanging and clicking. And when coming to a stop, the transition feels like there's a grinding feel.
I also do hear the same circuit board noise that you heard while in the garage, I figured that it was 'thinking' - even while OFF. It immediately stopped after pressing the lock button on the key fob. just my experience in the last 2 months.