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How to program my Prius to override automatic switching to outside air mode (want recirc)?

After purchasing my new 2012 Prius liftback, I discovered that the Prius air inlet mode automatically and randomly switches between recirculate and outside air mode (in cold weather). This means that without warning, the Prius will switch to outside air mode, forcing me to inhale exhaust from the vehicle in front of me, which gives me an asthma attack.

Toyota claims this design feature cannot be fixed. However, on the 2010 Prius, which is the same generation as my 2012 Prius, it is possible to use Toyota’s diagnostic software Techstream Lite to set the air inlet mode to manual, overriding the automatic switching to outside air mode. In addition, for the 2012 Prius, this air inlet mode customization is available on Priuses sold in Korea and Mexico:

I have received no assistance from Toyota on this matter, and now that the cold weather has arrived, driving my Prius has become unbearable due to the automatic switching to outside air mode (I’ve already suffered an asthma attack as a result of exhaust entering the cabin). I guess I have 2 options: sell my Prius or figure out how to fix this myself. Can anyone point me in the right direction about how to edit the Prius software? It would be helpful to see how the manual recirc override in the 2012 Prius in Mexico and Korea is programmed and/or how the 2010 US Prius override is programmed. I would greatly appreciate any assistance!

Also, is this the kind of question Click and Clack might answer? If so, should I submit it as a question for their column or “ask a puzzler” or…?

thanks :slight_smile:

Can you read Korean or Spanish? If so, perhaps you could contact a dealer from Korea or Mexico and get the programming instructions from them. I’m sure they can be contacted on the internet. Accepting, of course, that there may be unintended consequences to your other functions…the U.S, version may have some variant of their system.

There must be some kind of motor-operated or vacuum-operated door that’s used to pick one source or the other. Perhaps you could disconnect whatever controls that door and force it into one mode all of the time regardless of what the climate control system orders. That might take quite a bit of dash disassembly, though. You might end up with error messages of some sort. Your defrosting performance would suffer, also.

Don’t put the climate control in automatic, just select fan speed and temp, put the recirc on and it should stay on. Keep defroster off as well.

WheresRick, my climate control is not set to automatic. The automatic switching occurs in temperatures below 40 F.

mountainbike, yo hablo un poco español, but my understanding is that the actual coding is done at the corporate level, and that the dealers are just downloading software updates and don’t access the actual code, which is what I would need to see. The manual air inlet mode customization is available for the 2010 US Prius. I asked Toyota Corporate for access to the software programming, and they refused, saying it was proprietary.

Have you posted the on a Prius forum like Priuschat?

Im not sure our 2013 does that, I will investigate…

A talented hacker could start with what @lion9car suggested plus add a switch on the dashboard to enable/disable the air control door.
Try talking to a good aftermarket stereo installation shop.

Can you get a HEPA filter to replace your cabin air filter? That will collect particulate air contamination. You would need an activated charcoal or zeolite filter for airborne molecular contamination.

Bummer. Often there are protocols for reprogramming functions of various modules, and my thinking was that perhaps there was one in the native language of the countries where this was offered, but it sounds like you’ve already checked.

If I come up with any other ideas I’ll post. Otherwise all I can di is wish you the best of luck.

I’m wary of disconnecting the air control door since I do use outside air mode to defrost when necessary as long as I’m not close behind another car.

I have zero background in the mechanical aspects of cars, so adding a switch to enable/disable the air control door sounds beyond my capability. I do have some programming experience, so that’s why I was hoping to modify the code that governs the air inlet mode.

Given the complexity of modern cars, especially the Prius, I would recommend you not modify the wiring.

Have you asked this on a Prius forum?

I worry about hacking the brains of the car…you get it wrong, and you have a huge, non-warranty fix on your hands. I also worry about a “HAL-9000”-esque snit if the ECU finds the actuator isn’t behaving the way it expects.

If the recirc door is at all accessible, have somebody disconnect the actutor motor and hang it out of the way with zip-ties. Then rig up a pushrod/bellcrank assembly to manually actuate it. (Or a spare actuator powered by a 3-way “Shack” switch.)

Doubtful the car “checks for plausibility” on such a peripheral function: it should be fat and happy, playing with its own actuator, while you retain manual control.

P.S. Realize, too, that the car is not airtight, and all running with recirc on does is “average out” the air you breathe: instead of really clean air most of the time (followed by really dirty air when behind a polluter), you get mediocre air the whole way…and you have to contend with “stale air”: foggy windows and recycled pastrami belches!

I like the idea of adding a switch in line with the door motor. No modifications to the wiring would be needed if the motor has spade terminals. Plus you can make your own HEPA filters out of home heating filters.

I agree with Texases. I’m against butchering the wiring on modern vehicles.

And I like his idea about checking on Prius forums. The Prius has its own subculture, and it’s very likely that your question has been addressed before and information published on a Prius forum.

I posted on the PriusChat forums, and it was members there who alerted me to the customizations available on the 2010 US Prius and the 2012 Prius sold in Korea and Mexico, but I didn’t get any further suggestions on how I can fix this myself:

At the risk of stating the obvious, @Asthmatic, if it can’t be done, it can’t be done!

You’ve done an awful lot of legwork into this, and have run into multiple stone walls. Given that, you have a choice of living with it, or finding an alternate means of accomplishing your goal.

I understand such a fix lies outside your skill-set, but that’s why people specialize in things: can’t be good at everything, but you CAN find somebody who is.

Set your trunk monkey loose on the polluter in front of you. He/She could give them a good bop on the head.

Warm up the sensor which tells your car what the temperature is.