[WARNING] Running out of gas (Gen III)

When you are getting over 40 MPG 20 to 30 cents a gallon docent make a big diff. Im 72 and living on Social Security and I can do it. My road trips are usually around 1200 miles one way.

 

I.e. there is not much price differential in your area. My travels easily see spreads of 50 - 70 cents per gallon. In my normal shopping zip code, the price spread this morning is 92 cent/gallon.

Some normal intelligent people are more geared towards planning and cost optimizations and other math puzzles than others.

 

I like to think i'm a normal intelligent person but thats probably up for debate. If I thought I was going to run out of gas I would get 1 or 2 gal of the expensive gas till I could get to the cheeper stuff. I guess I'm a little old school. I spent 10 years in the Army, 6 years as a volunteer fireman, and about 18 years driving a 18 wheeler all over the US. I like to keep my gas tanks fairly full in case of a emergency. Planning and cost optimizations and other math puzzles are great as long as they don't put you,your family, or other in danger when you run out of gas in traffic.

 

i always imagine myself being chased by terrorists. i'm trying to find a police station, and the last thing i want to do is run out of gas.

 

I put a much more detailed response in the other thread. No, I don't run out of gas in traffic, and don't endanger people.

As for getting 1 or 2 gallons of expensive gas to tide over to the cheaper stuff, I'll just mention one of my highly formative experiences, a long trip in a sparsely served rural area, when a very major holiday coincided with a Sunday (31 years ago last week). When unexpected events left me with an untopped tank, I planed about 40 miles ahead to top off in a certain town. However, all stations but one closed for the holiday, its price was jacked up by the boss, and the 'entrepreneurial' clerk added a mandatory 'pump unlock' fee equal to more than half a tank.

Knowing what little I knew then, with fuel gauge just above 1/2 tank on a short-ranged car, I said no thanks and sweated the 130 more miles to the next station (with tourist trap prices) that was certain to be open. Had I known then what I know now about fuel gauging and hypermiling, I'd have given him a hardy 'You're Number One' salute, more merrily left him behind, then sailed beyond the tourist trap too to another place beyond with more reasonable prices.

There have also been other formative experiences, including the OPEC oil embargo four decades ago. Some places had rationing plans where many people could not legally buy any fuel on certain days, regardless of travel need. Knowing a vehicle's real fuel range, in advance, was highly valuable.

 

Any idea if anyone has run out of gas in the Prius Plug-in? I'm still curious to know if when the gas motor shuts off the remaining EV miles are usable or if it behaves like the non plug-in model.

 

i haven't heard or seen anything. it would be interesting to run it dry with a full charge. i already did it in a gen II, someone else's turn.

 

What the heck, I'll try running out of gas on my GenII and see what happens.......for fun

 

it's no big deal, just have 3 gallons of gas with you, and stop on level ground.

 

Yes, I know this thread is a zillion years old.
Yes, I know that it's 25 pages long (I read every page).

On the other hand, this thread is the "gold standard" that people are still referred to from other threads (in fact, just last week that happened) and so I have a question. It's probably a question that Bob Wilson can answer, so if you know him, please point him this way!

Question: As one who often stretches the range of the Prius (please, no replies indicating that's stupid), I live by the idea that there are 2.1 gallons left when the flash begins, per @bwilson4web 's testing. But earlier in the thread, it is indicated that once ran out after just 25 miles.

Since that is less than 12.5 MPG (which seems improbable), I am curious whether there is a logical explanation for this result or whether it is an outlier that should be disregarded as faulty data.

 

With just a little gas sloshing around in the bottom of the tank, maybe it sucked air while going up or down a steep incline?

 

Many variables to cause one to completely run out of gas around 25 miles after DTE is 0:

Any combination of driving downhill, headlights + AC or heater on full blast, non-top tier gasoline in tank, low tire air pressure, driving against weather elements, driving over 65 mph, constant change of driving speed, car maintenance, car has become less efficient over the years, and etc.

 

I think if gas tank cam was a thing, if owners could see the few cups of gas left in the bottom of the tank, they'd be a lot less inclined to run it low.

I'll muzzle myself now, lol.

 

If they also saw the amount of sediment I had at 200k miles NEVER having my gas tank run out, that would also act as a deterrent:

What did you do to ur Gen III Prius today????

 

Do note that the 25 miles case was in his Gen1, NHW11. But most of this thread, your car, and the 2.1 gallons figure, are specific to Gen3. So that particular 25 mile case is easily dismissed as being from a different car model, not your Gen3 design.

That said, also beware that individual cars and their fuel gauging can be both different, and inconsistent. But the possible variation range has not been characterized here. That is one reason why so some much safety margin is built in that no Gen3 driver can honestly claim that they were not warned about low fuel.

Gen2, with its troublesome bladder is different, a few drivers have run out before the warning.


This thread remains the "gold standard" primarily because no one else has come along to put in even more effort to further refine the topic.

 

When I had my 2010, I often filled up beyond 11 gallons, sometimes even beyond 11.5 gallons using the knowledge from this thread of 2.1 gallons left when the flash begins. I'd make an educated guess on the mpgs I was getting for the remaining distance, accounting for warm up and short trips, cold temperatures, snow, hills, and so on to confidently use 11.5 gallons without running out.

This failed me once though. The car once ran out of gas going up a steep hill (~20% grade) soon after the blink started. I added about 1.9 gallons from a 2-gallon fuel container, needed to clear the code, then drove 5 miles to the nearest gas station. At the gas station I added 9.95 gallons, so doing the math, the car was starved of fuel on a steep uphill with about 2 gallons left in the tank. That's a good explanation for why Toyota needed to set the fuel warning and DTE=0 with that much gasoline left in the tank.

 

Bob's experiment sixteen years ago in this thread has come to also be cited lately for an idea that the power steering system warning light might be telling you something about the engine or fuel system.



For example, in another thread:

The basis, of course, was the combination of surprising facts Bob first reported: that there wasn't a check-engine light at the point the engine stopped supplying power, and that there was a steering warning light when the car eventually balked at moving.

Of course it's not really a good thing to have the idea going around that the power steering warning somehow conveys engine information. There is surely a good explanation for why the steering light was seen in Bob's test, but it won't be that, exactly; Bob's central purpose for the test was never to pin that explanation down, and it hasn't been completely pinned down to date.

Bob first reported the experiment in June of 2009, driving what had to be one of the earliest production 2010 model-year Prii. He does not report having any scan tool on hand for that test or using it to query the steering ECU for why the light was on.

Bob did a repeat test 14 months later using an Auto Enginuity scan tool to log data. The logged data only came from the ECM, but was enough to report this:

(The post quoted contains Bob's logged data, as .xls.)

Indeed, though we don't have logs from the power management control ECU, we have the ECM's measurement of incoming 12-volt voltage, and see that drop from 14.04 (a reasonable voltage while READY and supplied from the DC/DC converter) to 12.32 (suggesting the converter went offline leaving the 12-volt battery to shoulder the load) between two samples when the car speed also dropped from 9 MPH to zero, suggesting the MG inverters and the DC/DC converter all got shut down pretty much at once to save the remaining juice in the traction battery. (The sample interval seems to be about six seconds, so we don't have a precise picture here, but we do have a picture.)

Even that retest did not involve using a scan tool to ask the steering ECU why it lit the warning. The ECU does, however, monitor its incoming voltage (both at its IG terminal, supplied through the ECU-IG No. 2 fuse, and its PIG terminal, supplied through the 60 amp EPS fuse), and the trouble codes it can set include these:



So, I might guess that one or more of those codes had been set.

Not certain, though. Those codes all say "Power assist stopped", while Bob reported:

That suggests the explanation may be this note, one page later in the repair manual:



That probably means the best thing when people ask about the steering warning and what non-steering conditions it might "mean" would be to tell them that (if no C15xx or U0129/U0293/U1105 steering codes are reported) the light can be reporting an unexpected low reading on the steering's 12-volt supply while the car is READY, and to check for reasons the car's DC/DC converter could have shut down (among other possibilities of course).

It's straightforward to explain why it lit up for Bob. It wasn't because the fuel ran out, but the fuel running out was a reason the engine's ability to keep the traction battery charged was lost; continued draw from the traction battery without charging it caused the state of charge to reach a critical level, at which point the power management control ECU stopped the inverter/converter sections (including the MG inverters for motive power, and the DC/DC converter) from drawing traction battery power; shutdown of the DC/DC converter led the steering ECU to warn of reduced available power for steering.

A comment about the A/C got posted:

... but I don't think I saw anything from Bob at any point confirming the A/C compressor did keep running. Unless I missed that, what I'd expect is that all of the inverter sections drawing traction battery power just got shut down at once. But this thread might not have answered that question (if anyone ever asks) for sure. (Also, if it was the "reduced assist power" warning described in the note, then the steering assist wasn't exactly lost as Paul58 may have thought.)



The much more interesting question raised in this thread would be why other expected warning lights (I'd have expected at least the check-engine light when engine power stopped being available, and the triangle when battery usage got canceled, if not earlier) are not shown for a fuel-out condition.

 

This is unrelated, but can someone please explain how to post a new thread? I cannot figure it out, after much searching. Thanks
Jenny
Sorry to hijack this thread