Tom in Austin

I know many people on here don't like or have turned off the start-stop process that shuts off the engine at a stop light. So, please don't reply suggesting "turn it off" ...

My car has had new main and aux batteries in the past 12 months. What I'm experiencing is after driving about 15 miles on the freeway, exiting, and coming to a stop, the start-stop function goes through a cycle ... the engine stops, restarts, and then stops again, all within a few seconds. Then it settles down and behaves normally for however much more driving I do.

I'm not really worried about it, but when my wife's with me, she notices and asks if there's something wrong with the car. So, if someone else has experienced this I'd be interested in knowing what caused it and how you fixed it. I don't feel like paying hundreds of dollars to take it in for a diagnosis and repair estimate, but again, if someone knows what's going on it would be nice to know what's happening.

S_W222

Neither my pre-facelift or my facelift W222s have acted that way. The pre-faceted Auto start-stop function never worked on cold days and that was it, whereas the facelift W222 worked all the time. However, it always used to be a one stop and on start on traffic lights, never on off on like you described above, unless I release the brake too soon or let the vehicle roll a few more inches. In all cases, once I can the Auto start-stop function, it never stops again until the next stop sign or light, so I'd say there is something that is NOT normal with the way yours is acting.

JohnLane

Tom that behavior is not normal but good luck getting a tech to offer anything but what you don’t want to hear. Most complaints I experience with stop-start are solved with fresh batteries. I have also seen electric auto transmission pumps fail for check engine lights and odd behavior.

I had Peter provide software that has the car start up with previous settings intact. No need to press ‘sport’ for the transmission every time I start her up.

Stop-start being a solution in search of a problem from the get go that has added much expense and complexity to our cars to save a gallon of gas annually(??).

carlosinseattle

My 2017 would occassionallly do something similar to yours. I never got it fixed before trading it in. One thing I noticed is I had to use a lot more pedal force to engage auto hold than on other cars, including the car I now have. It might have something to do with how the pedal actuates the system.

ygmn

I bet it is some input for start/stop program.
One or more inputs to program logic is saying hay start engine.. then it works and says shut off engine.... and then continues to work.

some sensor/input that has to be met before it turns off and/or turns it back on.

Maybe brake pedal switch is wonky?
or whatever else the computers look at to decide to start and stop engine...

you need to know logic and/or check for codes that may have no set check engine light.

95Sinned420

Most people turn it off because of the weird things it does. There are so many variables it checks to turn on and off (ie, cabin air temp, proper voltage, seat belt sensor, brake pedal sensor, vehicle speed, etc. etc.)
So, if there is a glitchy sensor, such as brake pedal sensor, it may thing you've released the brake pedal and therefore starts the car, however, if its glitchy and then triggering the the brake is fully applied, then it will then stop the engine, and that cycle continues. Its even worse for very slow speed (such as parallel parking) where if you're inching your way, the car will turn on and off and cause terrible jolts..

I prefer it on and deal with the minor annoyances. I know how not confuse the system to trigger unwanted shut offs.

Tom in Austin

Thanks all, pretty much what I know ... lots of inputs/sensors involved in this system. I suppose the significant variable here is that the misbehavior only happens once, when it's first invoked. After that, works perfectly every time.