ERDTT = Engine Running Due To Temperature

Sounds reasonable. Here is the Ambient Temperature Sensor test graph from the 2010 Repair Manual:

 

Tricking the computer to think the temp is higher than it is, could cause abuse to the battery pack. It would be allowed to charge/discharge higher than the "safe" parameter. There is a reason it was programmed to act this way.

Having said that, it is good to have an option to mod it and use it wisely, if we know what we are doing.

 

In the Volt's case, there are many battery temperature sensors internally, and this single temperature sensor "only" controls the ERDTT and driver display temp. I say "only" in quotes because some people have suggested that may not entirely be the case.

The particularly frustrating part about this for Volt owners, is that the "ERDTT" condition is ONLY to help heat the cabin, despite the fact that the resistive heater is capable of doing that sufficiently without the engine running.

ERDTT is great for trips that exceed the battery range of the car: You're using waste engine heat to keep you warm instead of the battery's electrons, so you get more electric miles. However, on short trips, it just results in wasted gas.

The Volt also has a mode where the engine needs to run while the battery warms up, but that's after the battery is at a temperature of something like -15F, which requires a 24 hour cold soak at that temperature or colder without being plugged in.

In extremely cold temperatures, a "Battery Too Cold, Plug in To Warm" message is displayed on the Volt, but to date no person has ever seen it in "real world" conditions.

Back to the Prius, does it do this to help assist with cabin heating, or to warm up the battery to an acceptable temperature? Does the PiP have a resistive heater to use when the engine is not running, like the Volt?

 

I'd worry about this too. The engine-start-when-cold behavior wasn't put in the Volt and PiP just to annoy users. I would think that particularly the Volt engineers, with their design goal of using the ICE only to extend range and not to use it unless absolutely necessary, wouldn't have put this in unless they felt there was a very compelling technical reason.

 

No. The prototype had a heat pump, but that was removed in the production model. The ICE is the only source of heat in the PiP.

 

Thanks for the clarification.

It's possible that, when the battery is cold, the Prius engineers don't want to extract too much capacity from it. The ability for the battery to accept and provide current decreases with cold temperatures. Depending on the size of the battery, the power draw, and the temperature, there's likely situations where they decided running the engine to decrease the battery load was the best course of action.

This is what happens in the Volt when the battery is below -15F or so, after not being plugged in for a long time in very cold weather. As a result, the battery is only used to turn the motor to start the engine, and then the engine provides the majority of propulsion while the battery is heated. In the case of the Volt, this is rarely seen, and was really only observed this year in the good old "Polar Vortex" days

 

the pip doesn't always fire the ice at low temp, aswitnessed by member 'retired4999'. it's multifactorial, and we don't understand all the conditions or reasons. i would be careful not to abuse this. this also says something about used plug in hybrids, how is the buyer to know what abuse has taken place prior to owning?

 

I only know of one or two Volt owners that have done this. Many agree with you (including myself) about not unintentionally breaking something.

I would expect that, if the PiP did fire at low temp, it would be due to the temp of the battery, not necessarily the outside temp. Not knowing what "retired" observed exactly, though, I can only speculate.

 

he routinely drives in 10-20 below weather, all ev. but he charges in a 45 degree garage. some members can't make it down there street at 25 mph and 30 degrees without the ice coming on. i can almost always drive all ev down to zero degrees, but i'm in an unheated garage. it's frustrating when it comes on for short trips, and i'm not sure how it helps the battery since it shuts down within minutes of startup if you have the heat off.

 

The Prius engineers are probably using a bit of self regulation inherent in their design. Since the PiP battery is air temperature regulated, the battery pack sees larger temperature swings. Cold causes internal resistance to rise in Li-Ion as do most batteries. Increased internal resistance is also seen by the electronics as a sign of increased discharge (decreased capacity) and with air cooling not all modules have the same cooling or heating effect. For instance modules on the outside see more extreme temperature drops and don't benefit from being sandwiched in between other warm battery cells/modules. So the entire battery pack will be judged by the lowest common denominator - the coldest cell/module. If the battery pack is allowed to heat up gradually during a discharge, say by extremely slow acceleration then the outside cells/modules will gradually get some of the heat being generated by the interior cells/modules. These outside modules may also get heated up if the Sun is shining and warms up the cabin slightly.

Since the electronics see the increased internal resistance from the colder cells/modules their discharge/power trigger points are met fairly early and the ICE is fired up.

 

Torque can log IR of each battery modules along with ICE rpm. We can test that theory.

 

FWIW: Absolutely no worries since this single B9 sensor is used only for creature comfort in the Volt. The A4 Li-ion battery pack actually contains 16 temp sensors preventing any 'abuse' of the batter pack. I have had no issue using only the electric heat provided by K10 and have not had the need to manual select ICE-assisted heating by choosing either HOLD or MOUNTAIN mode this entire winter! Now that it is spring, I've already removed my fixed resistance 'fix' and returned the OEM B9 sensor in place. Will definitely be implementing this quick fix again next winter since I only had to remove a single screw on the Volt in order to access B9!

Cheers!

 

Somms, that's not what this thread suggests:
Battery heating DOES depend on ambient temperature/sensor

I know you posted in here as well. Was the OP's observations de-bunked, or is the jury still out?

 

Are you guys using pre-conditioning?

 

I precondition whenever possible. Gotta love a warm car when it's freezing out.

 

Doesn't that stop the ICE from starting? Oh, I guess not since the temp sensor is for outside temp.

 

Correct (and sorry for the late response). On the Volt the driver can configure the car to prevent the ICE from starting when it's plugged in though (2013 and newer), so you can remote start and come back to a toasty warm car with zero engine/gasoline use. But if it's below 15F outside, the engine still comes on. (GAH!) Seems like some further optimization could take place there via a small code rewrite!