Why Prius ECU can't reduce battery temperature while Dr Prius app can?

The fan is supposed to come on somewhere right around the temperature you're talking about 117 122 something so maybe you flip the doctor prius app too quickly . And I would have trouble thinking 120° is any kind of massive temperature for a big metal battery like this but be that as it may That's only a few degrees hotter than a person well 20° or so that's not very much so I can't imagine 120° would be any kind of serious not good situation.

 

Do not assume that the temperature thresholds Toyota selected for their fan program are the same as the thresholds set in the app for text display color.

 

May have a clogged battery blower wheel.

 

the ecu does reduce battery temps by changing the blower speed as necessary

 

I think that what Leadfoot means is that Toyota engineers don't consider 120° to be too high. The ecu will turn the fan on when it's programmed to, and will set codes if things go bad.

Yes, it's generally better to have the battery cooler, but the OE design has worked quite well for hundreds of thousands of Gen2's. You can play with the fan if you want. I ignore it and use the A/C when it makes sense to.

They likely had to balance noise from the fan (& power use) vs temperatures.

Posted via the PriusChat mobile app.

 

Yes that's part of it.

I don't know what temps Toyota thinks are okay. I do know that they spent a big bag of money figuring out how much cooling air the battery should get, and a lot of high-mileage cars on the street means they did pretty well as far as I'm concerned. I'm sure they didn't want noise complaints, and they didn't want the fans to wear out in 3 years and leave the battery totally unprotected after. We know they were on the hook to maintain very long warranties on the batteries themselves, so they were motivated to make it last. A delicate balance.

The bigger point is that the car ECU is running one set of code to keep that battery cool, and the Dr. Prius app is running completely unrelated code to display and evaluate those temperatures and say whether the car is OK or not. You are the only thing coordinating these disagreeing phenomena.

Because these are two disconnected systems doing different things with the same voltage and temperature data, they will always disagree slightly and give you reasons to doubt one or the other. That doesn't mean it isn't useful as a tool, just that you need to be ready to read between the lines.

 

Dr. Prius has to be running continuously in order to control the fan or else the cars ECUs take over.

 

I was under the impression that Dr. Prius (and Torque Pro) did not have any intelligence behind the battery fan override. This might not be too much of a concern if you override to run the fan at speed 6 (full speed) but if you set the speed to (say) 4 and the ECU wants 5 or 6, it won't be able to set the fan to the speed it wants until you stop running Dr.Prius. So there is that consideration.

 

The ideal Hybrid Battery temp for a Gen 2 and Gen 3 Prius is between 77°F-104°F. When the HV Battery is outside of this temperature range... the Hybrid Control ECU begins to throttle charge in and out of the Hybrid Battery due to how temps affect internal resistance and to protect the Hybrid Battery. You can watch this happen in real time by monitoring the MAX Charge Parameter in Dr. Prius. 33.5HP is the maximum charge allowed into the vehicle... when it is outside the ideal 77-104°F temp range the MAX Charge parameter will be less than 33.5 HP.

The Hybrid Battery fan kicks on low at about 100°F and stays off until that point.

At about 127°F... the Prius effectively stops using HV Battery power to propel the vehicle... the only time after this point the HV Battery provides power output or charge to it is under heavy acceleration or if the HV Battery is low.

At 132ish°F... the Prius HV Battery fan kicks on to high. Before that point... the fan is on at a quiet speed... but the Hybrid Control ECU will be taking other measures to keep the battery cool like severely restricting charge in and out of the Battery during Acceleration and Regenerative Braking.

The Red warning you're seeing at 120°F in Dr. Prius is arbitrary and just how @jacktheripper (Dr. Prius) programmed the app. It is not overheating... but the Hybrid Battery is not in it's ideal range.

Reconditioned Hybrid Batterys heat up very easily due to being an old battery and the wear causing increased Internal Resistance.

Everything you've experienced in your post is 100% normal and nothing is wrong.

This is false... the Hybrid Control ECU will override any external input whether from an app or from techstream during conditions that require the Hybrid Battery to be protected... If the Hybrid Battery is too cold... you can't even turn the fan on. (Tested when below 50°F)

If it's too hot (above 132°F) the fan will run on high no matter what. Up until 132°F the Hybrid Battery fan runs at a slow speed.

 

You’re making an assumption that may not be true: the fan can run at multiple speeds and it’s not that audible.