A mysterious nudge when stopped

[ether100]

Once every so often, when I'm stopped at a traffic light with my foot firmly on the brake, I feel a momentary nudge like something tried to push the car forward for a split second. The first time this happened, I thought that the car behind me had touched my rear bumper.

This doesn't happen very frequently, but it is a bit unusual. Has anyone else experienced this behavior?

 

[WattsUp]

Once every so often, when I'm stopped at a traffic light with my foot firmly on the brake, I feel a momentary nudge

Ghosts? :shock:

But, seriously, does this happen only on hills perhaps? After coming to a stop on a hill, after a moment or two, you can sometimes feel the "hill hold" feature activating. I suppose it could feel like a nudge. I believe it only takes a 3-5% incline to activate hill hold.

 

[ether100]

Thanks for the reply. This sounds like an intriguing theory, though the ghosts are possible too .

I will check the next time if I'm on an incline, but I think that this would be happening more often if it was due to the "hill hold" feature.

 

[hybridbear]

Once every so often, when I'm stopped at a traffic light with my foot firmly on the brake, I feel a momentary nudge like something tried to push the car forward for a split second. The first time this happened, I thought that the car behind me had touched my rear bumper.

This doesn't happen very frequently, but it is a bit unusual. Has anyone else experienced this behavior?

Yes!! I've had this happen numerous times. I think it has to do with how hard you're pressing on the brake. Remember that Ford programmed in "idle creep" to mimic the behavior of an ICE car with a torque converter. When you're stopped the electric motor is idle and the brake pads are engaged to keep you stationary. But as you release pressure on the brake pedal the electric motor begins to consume electricity and supply torque to the wheels, pushing against the brake pads which are now only slightly pressed against the rotor to keep you stationary. This is how you can have the Focus creep forward while your foot is still on the brake. Normally when you step on the brake pedal the car is using the electric motor for regen braking, but at low speeds the electric motor just disengages (as if you were in Neutral) and then it engages again for idle creep.

I think this bump has to do with when your pressure on the brake pedal is right near the tipping point for when the electric motor provides idle creep. Since I always back off on the brake pedal pressure right before stopping to have a smooth stop I sometimes get this where the car stops but then the idle creep kicks in and nudges it slightly. I've learned to just be quick to press the pedal down hard once I come to a complete stop so that it doesn't do this.

 

[ether100]

Thanks hybridbear, that definitely sounds plausible. Based upon what you're saying, it should be possible to reproduce this condition deliberately. However, I tried today and got no nudge.