Third Gen Prius Surging on Highway in Cold Weather

I read lots of other threads about Gen 2 Prii surging (here and here) which seem to be similar to what we experienced last night. However, I didn't find any threads about something like this happening with Gen 3.

The outside temp was about -10F, the ICE was warm with a coolant temp of about 185F thanks to grille blocking. We were driving on the freeway at about 55-60 MPH when the car started surging. The Energy Monitor screen would show the arrows going back and forth between charging the HVB and using power from the HVB. Each surge would last about 1 sec. The speedometer didn't change during the surging periods but it was very noticeable inside the car. My ScanGauge would show the amps to the HVB rapidly alternating with each pulse. The surge would show about 20 amps flowing from the HVB to the electric motor. Then the drag portion would show about 20-25 amps flowing from the motor to the HVB. The SGII amp reading corresponded with the shift in the arrows on the Energy Monitor screen.

I didn't have RPM up on my SGII but there was no noticeable change in RPM during these surges. I had HP, LOD, WT and AMPS. There was no change in HP or LOD during the surges which leads me to be confident that the RPM wasn't changing.

The car seemed to be confused about what to do with the battery. At the time the HVB temp was <15F according to the ScanGauge.

Normally driving on the freeway like this the HVB would be basically disconnected. Usually I'll just see the Energy Monitor showing the ICE connected to the wheels and occasional flow to or from the HVB. During the surging stretch the flow to the HVB was constant.

The surging happened both using cruise control and driving with my foot.

I tried speeding up and the surging continued once I settled in at a higher speed (65 MPH). I tried slowing down and the surging continued once I settled in at a lower speed (50 MPH). I slowed down enough that the ICE shut off and then accelerated back up to freeway speed and the surging immediately returned.

The surging only seemed to happen when the ICE was producing 15-20 HP according to the SGII. If I pressed the pedal more to accelerate the pulsing went away. If I let off the pedal and power demand dropped below the center line on the dash then the surging stopped.

Based on the PSD simulation here I don't quite understand what was happening with MG1, MG2, the ICE and the PSD during these surges. Before I do anything with the dealer, I would like to understand what was going on with the PSD. I have yet to find a competent dealer for any brand of car so I don't have high expectations for getting help from a dealer...

Once we got off the freeway and were in the city the ICE didn't seem to pulse at the same HP output, although in the city it's rare to drive with that level of load on the ICE. I usually either am accelerating up close to the PWR area or am coasting in EV Mode.

Our Prius has just over 4000 miles on it, we got it in Sept 2013. As you can see on the left, it's the Persona with the 17-inch wheels. I doubt the wheels have anything to do with it but I want to share all possibly relevant information.

Does anyone have any ideas?

 

Interesting idea, but how does that explain why the surging went away at different RPMs? It's also been colder than the temp last night on this tank of gas without issues. Current tank level is just under half. Next week we're supposed to see -22F (-30C) so we'll see how the car does then. It's parked underground in a warm garage at our apartment so each morning the temp is about 60F when starting out in the winter.

If it is water in the fuel I would expect to see this issue show up on our FFH then too. I filled both cars at the same time last week from the same gas station. The FFH hasn't been driven in a few days, but I'll be using it today. Tomorrow will be interesting to see after it sits during the day at work with the high temp predicted of -3F tomorrow.

 

Good idea, but no. SOC was high. The Gen 3 gets loud when charging too, but this is rare. And it doesn't pulsate when charging.

 

But did the Lexus pulse the electric motor in and out?

 

Thank you. I don't drive the Prius often, but I asked my wife to pay attention and see if she notices it. Driving the Fusion this morning with temps of -5F there was no strange behavior from it to indicate bad gas, but that doesn't mean the gas isn't the culprit on the Prius.

Our 5000 "service" (i.e. tire rotation) is coming up in about a month. If the surging continues, I will document future occurrences more thoroughly, perhaps with cell phone video, to be able to show the dealer.

 

This would happen in 1 second increments? It's normal for it to come in & out, but not on and off every second like we experienced.

 

Based on the PSD animation I linked above, MG1 speed is based on ICE RPM. During these pulses, the ICE RPM and vehicle speed were constant. That's what confuses me about what was happening.

 

The surging has not repeated itself in the past two weeks. Hopefully this was just a one-time software glitch and it won't happen again.

 

Our surging has not presented itself again. The past few days have been similarly cold again and next week is supposed to be all below 0F so it might happen again. What was the air temp when your surging happened?