ENGINE STALL AFTER A/C GOES WARM. NO CODES, NO CHECK ENGINE

Hi Folks:

I drive a 2005 Prius with 255000 miles. I'm in Tucson Az, and it's getting to 105F outside. This problem
just started. In the weeks before temps were reaching 116F and the car took it like a champ. This is new.
Last night when it was 95F outside, I noticed my air conditioning go soft, then blew nothing but hot air. I turned
it off and drove for another 10 min or so. Out of nowhere, the console displays blink out, and the car coasts
to a halt with a strange grinding sound. Just before coming to a stop, the car jerks to a halt. The car is now
turned off. When I power back up, no warning lights, no check engine light, no triangle of death. I'm able to change gear and move the car. A about 5 min later, the cycle repeats.

The engine was hot. No doubt about it. I topped off with some pink coolant from Autozone, and I was able to make it home without further incident. I then tested in the cooler AM air, then again in the hot 108F heat of the day. Oil and coolant levels were fine. In the 108F heat of the day, the same cascade of events. After 20 min of use, the A/C warmed up, then I turned it off. I transitioned to back streets and had a stall out event. Again, no check engine lights or triangle of death after a restart. This time I had a ODB2 reader attached and noticed that the reported engine temp held between 85C and 88C when everything worked fine. The A/C went warm when the engine temp went above 91C. The stall out and grinding to a halt happened ~92C.

Symptoms leading up to stallout:

A/C goes warm

Many electrics blink out.

System reboots itself most of the time.

System reboots up just fine. Or I can restart it and it's 'fine'.

Grinding noise during coast to halt.

Jerking at final halt.

Additional Details (Unrelated?)
Aux battery sometimes has low voltage and system does not execute a proper shutdown sequence.
When this happens, I need to 'jump start' the system with external power via front relay box.

I recently re-capped the multifunction board. Board gave out in the high heat of this summer. Job was done two weeks before the onset of this problem. This board is giving perfect service now.

Andrew Tubbiolo
2005 Prius.
255500 miles.

 

OBD2:

It's a cheesy scanner from Asia. Do you have a scanner to recommend? I'd like one that I could interface with with my laptop or a ras-pi. I'd like to avoid dependence on Google Play or Apple ApStore. So I need to cover this issue. It's a real point.

Inverter Cooler Pump:

I replaced it last year. I'll check inverter coolant flow. If that did stop, wouldn't that throw a check engine light?

Andrew Tubbiolo
2005 Prius.
255500 miles.
48 MPG measured by gas consumed.

 

Yes, there are no warning lights after a restart. As the system is crashing they sometimes all
light up, but still no triangle of death. In today's test run when the system collapsed all the
warning lights lit with the check engine light. That was for about a second before the shutdown.
Then after shutdown, everything comes up 'fine'.

Was the inverter coolant pump replaced with an OEM part? I don't know. I purchased it from a
friends spares store as he owns a Prius fleet for his family. Good question there. I'll explore that.
If it was not are you saying that there could be a failure with no flagged errors?

Andrew

 

Just checked this. Started up the system and opened the coolant tank. No turbulence AND no pump sounds. So just to make sure it was not because the engine was totally cold soaked from sitting overnight, I turned on the AC and drove to a drive thru fast food joint (for scientific purposes of course) to get things warmed up. When I returned home, I placed the car in park, popped the hood, and again, no turbulence and again no pumping sounds. As a clincher, I turned off the car expecting to hear the coolant pump go thru its shutdown sequence, and nothing. So no matter what, I need to replace the inverter coolant pump.

Andrew

 

Oooohhhh, thanks for the correction. It was 93F out when I did the test. A bit chilly for Tucson I wonder why the engine is not hording heat on shutdown .

Andrew

 

Hi Folks:

I changed the inverter coolant pump with a genuine Toyota part purchased at the dealership. In short, that was it. Almost all the problems I'd been having with the car are gone. With the exception after short drives, I still have to jump start the car from the front relay box. This is not happening a lot but after long period of idle time (like 4 days) or multiple short trips. It's a brand new aux battery so still some issues to chase down. However, the car is very much usable again. Thanks for all your help. I waited a few weeks to 'close out' this post just in case the problems came back.

Andrew