Gliding issue

I have owned my 2012 Prius v wagon for a year and a half and I've had the ScanGauge II almost as long. My commute to work is : 33 mi, 40-45 mins, 90% freeway one way.

I'm beginning to notice an inconsistent issue while gliding on the same downhills every day. Normally, I get 9999 mpg/ 0.00 gph easily while the ICE idles at 992 rpm. Lately (randomly), it won't go into 9999 mpg but 200ish mpg intead with the gph at 0.36. My first glide is for about a mile after driving for about 15 minutes. I called it inconsistent because because one day I get 0.00 gph, the next 0.36.

It doesn't appear to be related to temperature since the issue happens at 45*F or 56*F. The coolant temp is 190-195 and SoC is at 59-60% fairly consistently. It doesn't matter if I'm driving with cabin heat on (not defrost, fan on low) mode and headlights off. I do have a Garmin GPS pluged into the 12v outlet. However, unplugging it doesn't affect the outcome.

One more thing... on the same drive it may finally go into a 0.00 gph glide later and then back to 0.36 gph at a later point. And, to complicate the issue... the SG will sometimes show 0.02 gph while in EV mode.

I know that issues like this are tough to diagnose on a forum but I'm hoping that someone may have run into the same problem and figured out the problem.

Is this an issue with the ECU reporting inaccurate gph at times? SG issue? 12v needing extra recharging? an airmass flow sensor issue? Throttle position sensor issue? Any clue?

 

Great question. It has no effect. With the high temps in the 50's in the PNW, I don't use the heater that often.

 

Good to know. Mine is doing it 1/2 to 2/3 of the time. On EV, now I see 0.02 gph the majority of the time. I wonder if a CTL-ALT-DEL (disconnect the 12v batt) would help clear a glitch with one of the sensors.

 

Thanks. That makes sense. I'll try the Xgauge GPH.

Today with temps in the low 40's and using cabin heat I could easily get 9999 mpg/ 0.00 gph. Go figure.

 

Tire pressures? Ok. What should I look for?

 

In the process of trying to figure out this mystery, I notice that the SG is reporting horsepower even when the car is in READY mode parking brake set. It shows 0.2 hp along with a fuel flow of 0.02 gph. I'm beginning to think that this erroneous horsepower reading is the source of the problem. When I finally get to see 9999 mpg, the horsepower indicates 0.0 instead of 0.2 Maybe others can verify this when you don't see the 9999 mpg when gliding.

Does anyone know if horsepower is reported by the ECU? Or is this calculated by the SG?

In either case, I'm going to send my SGII for the 4.02 firmware update.

 

Dave,

Sorry. I have not send it yet. It's still a mystery to me as to when the SG decides to show 9999 or not. On my commute home today, it would show 9999 mpg. I'm pretty much convinced that this is just a Scangauge glitch. I'm still seeing consistently spectacular trip mpg's (59 mpg on the way to work yesterday with no traffic and 65.6 with rush hour traffic today) whether I get 9999 mpg or 250 mpg on the Scangauge.