Grabaman

I was driving from Sacramento to South Lake Tahoe late yesterday afternoon. It was about 90 degrees. As I'm heading up to El Dorado Hills on HWY 50 at about 75 mph (pretty steep grade), the climate control temperature, on its own, goes from a nice 75 degrees to HI and starts blowing hot air ... pushing the up/down temp buttons does nothing. I crest the hill go down a little bit. Turn the climate control off and back on and I get it back to 75 and all is OK. Same general thing happens as I'm leaving Placerville.

Is this some kind of self-protection mode? Is the engine or part of the hybrid system overheating? I'm sure plenty of people drive in hotter temperatures ... though I will admit it was pretty warm and a pretty good load, but dang I wouldn't think that a 2013 Lexus would require cooling system tricks like a 1980s vanagon in 90 degree weather. I have only owned this car since September so this was one of the hotter days I've used the car. (I did drive from South Lake Tahoe to San Diego and back in September/October with surfboards on top, irutal winds, and a car full of gear without issues, but don't recall specific temps along the way.)

No CELs or other warning lights. Car was just at a Toyota Dealer for 60K service (~61K miles now) and everything checked out. Has been all good (except for sunroof in hot weather) til this slightly troubling event. I'm not sure of the condition of the 12V battery, it could be original. I've read that a bad 12V battery can lead to all sorts of trouble. The car did sit in my garage for over a month untouched during the snows of February, and it started right up and ran fine.

Thanks much,

Tom

ltsr

The behavior from the car sounds logically correct. The car should essentially turn on the heater to purge the hot air at the radiator through the vents. I'm just a bit surprised that lexus actually did this. If we compare to other manufacturers, for example BMW. Instead of doing what lexus did by purging the heat, BMW would make the car will go into limp mode and dangerously decrease your speed while on the highway. I would think that toyota/lexus logic makes more sense. I had my old E46 M3 go into limp mode while on the highway at 70mph on a steep grade and it was pretty nerve wracking have to pull into a tiny shoulder while 18-wheelers are flying by me at 60-80mph.

E46CT

^you are assuming this is by design and not simply an HVAC malfunction. i've never heard of any car doing this by design and i searched prius forums and nothing there.

also if your e46 M3 went into limp mode, I don't think it was due to overheating. likely fuel starvation, lean condition, or SMG transmission issue (if you had smg).

ltsr

I think my assumption is sane and logical based on the behavior explained by the OP. If it is just an HVAC malfunction, it happened at a very specific time and condition -- this is what makes my guess logical. Your guess with HVAC malfunction does not make a good argument but a blind guess given the conditions provided by the OP.

My E46 m3 went into limp mode with a bad TPS. I was in a brand new 2011 bmw 335i that overheated and it went into limp mode to try and save the engine. Throttle input was limited.

Grabaman

Thanks for the thoughts. It seemed like a specific time to me but at the same time, not that specific as conditions stayed relatively similar for 20 - 30 minutes and then did it again. It could certainly be HVAC malfunction. That's why I threw out the reminder that I have another intermittent issue (sunroof) that is heat related - not sure on the age of the 12V battery. Guess I'm hoping for an easy answer rather than needing new climate control head and a new sunroof motor in a 60k mile car! I too searched prius forums and didn't see anything. I found a few issues with CT climate control but it seemed related to stuck buttons not doing its own thing....

Again I appreciate guesses/hypthoses/experience.

-Tom

E46CT

I did not guess HVAC malfunction, I simply implied it does not make sense to assume OP's limp mode was triggered (by design) an overheat, rather than just a coincidence--such as--a malfunction--or in this case--an HVAC malfunction.

Yes logically turning on the heater is how you'd typically mitigate an engine overheat scenario, but that's done by the driver and not the car. And that would typically mitigate an ICE overheat, not one of the hybrid system for which it has its own cooling system. I've never heard of the car doing that because by purposely designing that into a car comes with a whole other set of problems.

Not ruling it out, just saying it would be very highly unlikely and a bit far fetched to assume it was by design.

I just think OP had an electronic hiccup of some sort

The initial assertion here is that there's a connection. "I am surprised Lexus did this."

What can be asserted without evidence can be dismissed without evidence.

ltsr

Your guess is as good as mine

E46CT

you're the only one that made a guess. i'm just saying it was strange for you to guess x rather than y.

it's like you guessing aliens swooped down and turned on his heater and me implying it could be a malfunction and stating welp we both could be right.

cars don't work like that.

ltsr

Here's a snippet from the CT200 techdoc:



maybe your HVAC guess is partially correct

OP, if you need snippets from the techdoc, I can possibly help if you want to dig into it further.

Grabaman

Thanks ... looks like there are several failures that could result in max temp. I'm not familiar with the TechDoc but am interested. It seems like I should be able to get some codes somewhere to help narrow down the failure.

-TOm

ltsr

You may have to get something more advanced like techstream to pull the code.

Here's the list of codes available for the CT200h:



If you can pull the code and let me know I can get assist with the issue the code pertains to.

Grabaman

I took the car to a toyota / lexus independent mechanic. He looked things over and scanned the computer systems. Everything looked OK, a/c works fine, and no codes were found.

He did mention the car has aftermarket HID lights and suggested returning that to stock to rule them out of the equation as they may be significant draw. I said I'd take a look and see if it's something I can do. (when the climate control over ride happened, it was day light and I don't think the low beams were on (I leave the light setting on auto)).

Any thoughts on the reality of the HIDs being related to the climate control?

In the meantime, I'll keep driving.

Thanks, Tom

ltsr

I don't think the HID lights are related but I don't want to guess, I might get roasted by @E46CT

If you can find a fault code at some point, i'd be curious and willing to help dig further.