Scared to know what is wrong... is my baby dying at 237k? Mass air flow sensor?

2009 Prius here.

Way back on July 20th (just over a month ago), I got the codes from the car after seeing the dreaded RED triangle. Car had produced the Red Triangle once or twice, but it went away after resting.

Code was P2103.

Eventually, I brought it to the dealer to diagnose, and they concluded the car needed a throttle body actuator? (part TO22030-21020) and mass air flow sensor (part TO22204-22010), along with a gasket. Claimed it wasn't a safety issue to drive. Estimated cost $1000-1500 to repair. I went home and asked my non-dealer mechanic if that was something they could repair cheaper. They suggested replacing the throttle body first, then seeing if sensor was bad... incremental repairs. I agreed.

Throttle body was replaced August 23rd and I was hopeful that was all it needed. Nope.

Yesterday, August 28th, after running the car about 3 hours (half while idling with a/c on), the same warning signs appeared:

red triangle,
check engine,
funny red car with exclamation point through it on display window,
sometimes VCS light,
sometimes ABS light,
sometimes orange circle with exclamation point in it,
sometimes traction icon

Thinking I knew what the issue was, I called the garage to tell them to order the sensor, and I kept driving.

Well - the car did not like that at all...

For 20 miles to get home, I turned on my hazards because the car would "quit" and lose power unexpectedly. The BRAKE light would come on, the car would scream a non-stop beeeeeeeeeeeeep noise and be hard to actually get the car to quit. A horrifying message came on the display about how the car couldn't recognize the PARK setting, so I should get somewhere level and use the emergency brake. I would coast to the side of the road, turn the car off, wait a bit, turn it on, and continue.

Eventually, I figured out that the car was not "dying", it was slipping into Neutral gear. I would sometimes be able to re-set it to Drive without stopping all the way. But it got worse and worse...

I would stop, set the emergency brake, turn car off, wait, turn car on, release brake, put in drive and go.

ALL THIS, so I could avoid a tow... But my hazard lights apparently wore down the 12v battery and eventually the car TOTALLY died 4 miles from home. AAA rescued me, powered the battery, drove the car onto the tow truck and it's at the garage now. I don't know why I didn't think about the hazard lights. It was HOT out and we drove with no a/c, no radio, nothing, in order to limp home. I know better than to run down the 12v, but didn't realize hazards were draining.

Something tells me this is not merely a sensor issue???

Do I even want to know what it might be??

Car has been rock solid up to 237k. I was so happy, I changed spark plugs and PCV valve earlier this summer, thinking I was good for another 100k.


P.S. Also this summer, I did have a fuse issue (solved here!) after the wires for the damaged rear view mirror touched and shorted out a fuse. I believe that issue was solved and is unrelated to this - but just in case, I'll note it here. Also replaced cabin air filter this summer with cheap Amazon filter. Found acorns in there.

 

12v battery I believe is original... for sure not replaced in over 120k miles (4 years since I bought it at about 115k). Have occasionally run it down in some fashion (2-5 times during those 4 years), but not recently. Does it have an alternator like "regular" cars? Are you saying that could be the issue of the day unrelated to MAF sensor?

 

On 8/2 when dealer diagnosed MAF issue, they note "Test battery with medtronics battery tester and record" Ditto when they changed the fuse on 8/19 (I didn't know it was a fuse, all lights on and power steering gone - but you dxed the fuse and that was all it was). Not sure which battery they mean, but assume 12v?

EDIT: They checked some battery performance and said Factory Cold Cranking amps "345", nothing under "actual cold cranking amps" and marked it as "GOOD"

 

Thank you - I should have done my own research on that alternator issue. I appreciate your time and the explanation. My mechanic shop is trustworthy, but not sure they have much modern Hybrid/EV experience. They will tell me if they are over their heads, but if I can point them in the right direction or confirm their findings I will feel better.

I'd like to get the current codes off there myself. Maybe I can swing by and get those while it sits at the shop and waits for the MAF sensor part.

 

Does the slip into Neutral indicate transmission? Guess I'll do some research on that one too...

 

Will check on transmission fluids.

Did not have the wherewithal to check my own codes while stuck in the middle of the road on saturday.

Mechanic tried to get codes off of it this morning and there were none - ZERO - which I think lends credence to it being a 12 volt battery problem, so they're picking one of those up. I think that battery tested at 7 volts this morning so I'm not sure what the heck the dealer tested last week... Grrrr.

 

12 volt battery was 7 years old, from 2014. Replace that, along with the air flow sensor and car is driving fine at the moment.

Thanks!

 

Sad to say that I drove it later today, which was very hot, and eventually the warning lights came back on again. The red triangle, the yellow orange circle with. "!" In it, the VSC light and the check engine light. Also my air conditioning seemed to go out and quit cooling. Fan still worked but was not blowing cool air any longer.

I was less than 5 mi from home so I drove home and stuck in my OBD2 reader with the free version of Dr Prius app.

I was able to get one code under the "Read battery errors" button. It said "HV battery ECU error code P0A93"

The " read engine code " button yielded no errors.

Sigh. I've searched the forum for that code and understand it can be related to the inverter water pump.

I guess the question I have is whether or not it could be related to the mass air flow sensor replacement which just happened today or the 12 volt battery replacement which also happened today... They had connected a battery charger to the fuse box post during some of this work, which I understand is in the area of the wiring for the inverter pump... I suppose I should check and see if anything looks Disturbed in that area.

Or do I really have a new problem? I guess I see that I'm supposed to take something apart and see if the liquid is bubbling or boiling in there. I'm not sure if I'm up for that or not.

I'm just pretty discouraged tonight. Not sure whether to try to get my regular mechanic to look further, or cough up the bucks and head back to the dealer... Aaargh!

 

Ok, I checked back with my regular shop and they did not replace the airflow sensor yesterday because the part wasn't in yet. I misunderstood.

So now I wonder if this whole issue was not the inverter water pump the whole time and maybe I don't need a mass air flow sensor! Similar lights came on to when the throttle body issue was happening, and I just assumed since the dealer had diagnosed that a while back that that was the reason for the lights. Maybe not.

 

Lesson learned!! But after zero lights for over 100k miles, I am new at having problems... I'll do better on my next Prius, lol.