Featured sudden speed loss

That's a tad scary. I would not hesitate to take that to the dealer.

 

Are you using cruise control? If so, the car will automatically slow down if it catches up to a slower vehicle in front of it, or if it gets confused and *thinks* it catches up.

 

if you press harder on the pedal does the speed not change?

 

I really don't understand the question. You're not using cruise control and the car is slowing down. When that happens to me, I just push down on the accelerator. A car will slow down for various reasons; increased wind resistance, slight grade increase, change in road surface, even heavy humidity. I know my Prime looses a few mpg's when it's raining vs my ICE cars gain a few mpg's in the rain.
OH; forgot the EV to HV switchover. I always have to start mashing the pedal when the car slips into HV mode.

 

^ The slight wind or grade increases can be quite unexpected and unobvious. For someone holding a fixed pedal position without cruise control, the effect is certainly significant.

Changes from dry to wet roads, or damp to more wet roads, also add up. Or even from in- to out-of-tire ruts, which significantly alters the water layer thickness.

 

Nope, never had that activity on a Prius Prime. You have, however, described what the car does when using the dynamic cruise control.

 

i'm wondering if the radar cruise control sensors are acting up, sensing there's a vehicle in front of you, although i think the throttle should still work, idk

 

What mode is the car in when this happens? EV or HV
If it's in HV mode, does the engine rev-up or nothing happens when you mash the pedal? How do you resolve this in traffic; pump the pedal or it just starts working all of a sudden? I wouldn't be driving a car in that kind of condition - take it to a mechanic ASAP. This would be a good way to get yourself T-boned in traffic; if it cut-out while trying to cross an intersection.

 

Fuel pump?

 

While not a Prius, we had a similar issue on a Isuzu Trooper many years ago. You mash the gas pedal and the car barely responds. Very dangerous. It turned out to be a clogged CAT! The exhaust simply could not escape, and back pressure would not let the engine wind up. I don't know how you'd diagnose this in a Prius, though. You seriously need to get your car to a qualified shop.

 

This sounds like how the accelerator remaps when you run out of EV range. It's pretty noticeable especially if you've got the drive mode set to ECO. If I was at say 3/4 throttle (or whatever you call it) driving EV and it switches to hybrid mode (HV) the throttle drops gradually over a few seconds to below 1/2. Often I find myself pushing into the red prw zone to maintain speed when it switches to HV like that going up an incline.

But if you're putting the pedal to the metal and still losing power then something is quite wrong.

 

how many miles on her? i wondering about the egr circuit, throttle body and maf, cat, etc. things that aren't considered normal maintenance

 

Are you in EV mode when this occurs? EV mode is downright enemic at high highway speeds.

 

but it should still accelerate or kick the engine on

 

While these are good guesses, the problem would be persistent rather than intermittent; unless the OP doesn't know which mode the car is in when the problem occurs. Issues above would only occur in HV mode.

Now if there's a "flat-spot"/defect on the accelerator pedal; this would occur in all modes. That's the reason for my questions above.

 

No, it doesn't. It stays in EV mode. It shouldn't slow down though, but if you are at max power for the electric motor, if you push the pedal to the floor it won't go any faster.


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