2010 Prius III MPG Loss - Experts - No Joes Please!

no joes? darn! that leaves me out.

i will say this, you can hook up mini vci and read a lot of metrics, including your hybrid battery status under load. all the best!

prius team lead investigator? he doesn't work weekends.

most of the 'i took my car in for service and when i got it back the mpg's were lower' threads, never come to a conclusion.

 

This is a case for Patrick Wong. I am out of this one.

 

Wow, one of the most thorough first posts I've seen yet...

I've got nothing.. You already answered everything I normally would say to check in a crappy mpg type question...

 

What do you have against people named Joe? Traumatic experience in the past?

 

I'm a Joe but I'll still weigh in on this issue. Since all this was immediately after your service, you can look at what your service included.

1. Was the oil change done with the proper weight oil 0w-20? Or did they give you what they had available 5w-30 or higher?
2. How did you get the dealership to re-check the spark plugs? Taking out the spark plug would be a couple hundred dollars on a Gen3
3. Were your tires rotated? Sometimes that will cause you to lose mpg after rotation
4. Did they have the proper fluid for the transaxle fluid change?
5. Just because you changed to a new yellow top battery, it does not mean it's a good battery.
6. Did you service the brakes? The brakes could be causing friction if you serviced them.
7. Lastly, it could be the gas you put in your car, the gas station may have switched to winter blend gas, which is lower energy than summer blend.

It also sounds like your hv battery could be losing some capacity. If it drains quickly, it would require more of the engine to stay on longer to charge it back up.

 

The battery indicators that you are placing so much faith in are indicating that there isn't a really serious problem. Has anyone checked the individual cell voltages in the traction battery? Get the mini-vci & Techstream so you can properly diagnose the car.

 

I also have a 2010 and I don't remember ever averaging 55mpg. My average with 17" wheels is usually around 45mpg, often less than that during the summer months when I use AC at full blast.

You seem very thorough on your research and what you've done so far to the car. I don't know what else would cause the drop in your superb mpg of 52-55mpg. You can maybe check the following but it's probably not going to improve significantly

1. Make sure the spark plugs are in fact OEM NGK or Denso plugs and the plugs are all gapped correctly.
2. Have you cleaned the throttle body and MAF sensor?
3. Do you have a new air filter?
4. Have you done an alignment and tire balancing?
5. What's your MPG without AC use?
6. Winter blend gas will definitely give you lower mpg
7. Did the dealer do a recall (inverter reprogramming) while it was in service?

I can't think of anything else. Anything outside of what I mentioned, would have to be HV battery related. It probably has lost capacity (mine definitely has) and it'll require your engine to run more than before.

 

This is the area of interest:

We need metrics and miniVCI is one of the first because it reads out Prius unique values. Would you have an ordinary OBD scanner already? Even a 'dumb' OBD scanner can give some values.

Do you have an opportunity to visit Art's Automotive or Luscious Garage? Both are well known and skilled in the San Francisco and Berkley area. There is a third closer in Southern California but I don't remember their name right now.

One thing you didn't mention is checking the radiator coolant. I had a problem with warm-up of our 2003 Prius that was cured by topping off the radiator (done cold!) and the overflow tank. This is just sharing, not a diagnosis.

Bob Wilson

 

I am definitely a Prius fan. It would be hard to post in this forum and not be a Prius fan.


42PSI in all 4 tires.

Computer problem (sensor inputs)as it should run on battery. Or throttle positioner assembly/electronics.

Possible thermostat issue.

But most likely an unplugged cable. Very common in a shop and will be an Easter egg hunt. Should throw a code so that has me puzzled. Check around the cable runs from the radiator/coolant sensors to the computer.

55MPG is about right with standard OEM LRR tires. I get 64MPG going to work everyday in my 12.

 

Does Prius have a second temp sensor? The one used by ECU? The only time I"'ve seem something like this was on Mitsubishi, and there weren't any error code On OBDII. Sensor was working just showing sub freezing temps. We only found this after it was hooked to dealer equipment.

I assume the oil level and tire pressure was ruled out.

But as an average Joe I'd better stay out of this

 

I care less if you want advice or not, it's a public forum, yer welcome

I've always suspected the actual relationship the computers have with the brakes, for example, when coasting if I just nudge the brake pedal the car seems to relax and speed up a bit, like the brakes are always just slightly engaged and possibly some are just stealing to much energy, err, regenerating when they shouldn't be.
Of course there's always the emergency brake cable, and yes the throttle body, and the egr valve

 

I'm not an "expert", per se, but the first thing I would do is check to see if the car is throwing any codes. That's where I would start - anything else would be mere guesswork...

 

It wouldn't hurt to feel all four wheels after an extended drive, see if one or more is markedly hotter, dragging. I'd put my money on the rears, if that was the issue.

The reluctance to shut down is the elephant in the room; very likely to be the direct cause of the mpg drop. As to why, who knows, I'm just an average joe.

 

I'm now leaning towards the HV battery dying an early prolonged death....??

Is it possible that no codes are getting thrown but the HV is indeed dying?

 

absolutely. in fact, the battery starts losing capacity the minute you drive off the lot. at some point, it may become noticeable, but not bad enough for the computer to throw a code, based on parameters.

 

I would suspect the thermostat is stuck open.

 

I vote for Cyclopathic's idea. Some dumb sensors (like the thermocouples used for temperature) might just give a strange reading if they were faulty or unplugged - there would be no code or indication that they weren't working correctly. Probably the best option would be to connect some sort of computer (I would think a Techstream can look up most everything, although a ScanGauge or other similar devices can check out at least some of them) and read out everything, and make sure the values all make sense - both with the engine off and cold, and once it has warmed up for 10-20 minutes. In addition to a faulty thermostat sensor, a faulty battery temperature sensor might cause similar symptoms, but I doubt that's what you've got (I would expect the engine to run 100% of the time in that case).

 

A brake not fully releasing