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This is brought over from another thread. The topic concerns the ability of the dealer to set the ERDTT to the lower setpoint on cars (2012 and earlier) that cannot do it via the config screen.

I've been told by the dealer that it not only depends on when the Volt was built but also the "Build". My son has a 2012 Volt that was built about 460 units after my Volt. I have my Volt set for the lower temperature, yest when trying to do the same thing for his Volt, we can't. When the dealer called GM about this, they repeated it depends on the build or what options you have in the car. In my Volt, I have all the options, NAV, Bose, heated seats, rear camera, etc. My son's Volt is a basic model with no options. I don't know which option or combination of options allows you to set the low temp settings.
This is pretty useful information. Thanks FrankIII.

In Toronto it was often below -3C but not often below -7C this winter. The ICE came on in all kinds of situations where it was not needed (e.g. I was very close to arriving home and plugging in to my 240V charger). And a lot more gas is burned when a cold engine runs for a few minutes. So I burned a fair amount of gas (probably about a full tank - horrors :)) needlessly over the past 2 months.

I have Bose but not the other 3 options you mention, and I cannot set to the lower temperature in my 2012 Volt. It would have been amazing if my dealer could do it.

Does anyone have further information/advice?
 

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I have my MY2013 set for ERDTT to kick in at 2C. I use about half a liter per day for heat in the cold weather for a cost of about 65 cents per day. On the coldest days I am almost certain that the cost of electricity vs. the cost of gas used is pretty much a wash due to the charge sustaining that also occurs while the engine is running and providing heat. I have a relatively short commute ( about 10km each way ) so mileage may vary for others but for me, having a toasty warm car is necessary and the cost difference between the recharge and the fuel used is not significant. I also think that running the ICE in the cold weather everyday keeps it lubed, keeps the gas fresh ( you will be forced to burn it anyway if you don't use it ) and gives me reason to change the oil about once per year knowing that I used it at least a little.

The way I see it, I am driving the volt like I would any other car I own(ed) and my savings based on that pattern are still very decent and the money I would have saved hypermiling is instead spent on simple comfort during the winter.

My pattern looks to be a tank to 2 tanks of gas from May to December and 2 tanks of gas from Jan to April for a total of about 4 tanks of gas per year. Electricity costs for me are about 50 cents per day in the winter and 1.00 per day in the summer so in the course of a year, I am about $1.00 per day for energy costs and all the while comfortable. I do not have the desire to try to save the $50 or so one might gain by always trying to be battery only in the winter.

I leave that much money in half full cups of cold coffee laying around... :)
 

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To get around this with my 2012 I wired in some resistors on a double pole double throw switch. When I see the temp near 25 I throw the switch that reads my resistors instead of outside temp.Temp reads 28 degrees with wired in resistors.
 

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Wow, I would love to have this done to my Volt. Really no reason why it cannot be done on all Volts as there is a 25F somewhere in the firmware. This value just need to be changed to a lower number.
 

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To get around this with my 2012 I wired in some resistors on a double pole double throw switch. When I see the temp near 25 I throw the switch that reads my resistors instead of outside temp.Temp reads 28 degrees with wired in resistors.
Bravo! Can you share some pics and part numbers? (or at least the number and ohms of the resistors?)
 

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To get around this with my 2012 I wired in some resistors on a double pole double throw switch. When I see the temp near 25 I throw the switch that reads my resistors instead of outside temp.Temp reads 28 degrees with wired in resistors.
you know when folks offer up info like this it would be useful to provide some info, photo's and parts list. Dropping a post like this w/o details is inviting posts like mine asking for info.

So how about sharing some real info?

Thanks
 

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Parts I bought to override erdtt. Radio shack; dpdt switch 2750663 $4.99, pc board 2760148 $2.49, resistor pack 2710312 $14.49 and some 22 gauge wire. Put two resistors in series to get the needed resistance 19,000 ohms (red,red,orange,gold) and 22,000 ohms (brown,white orange gold). 40,000 ohms will read at or around 28 degrees F. The two wires from the ambient temp switch go to the controller under the passenger seat, that is a convenient spot I chose to splice in. I am not sure how much of a discrepancy there can be between my 28F and actual outside temp before a dtc is set. I have only gotten to use this when the outside temp was 24F.
 

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Parts I bought to override erdtt. Radio shack; dpdt switch 2750663 $4.99, pc board 2760148 $2.49, resistor pack 2710312 $14.49 and some 22 gauge wire. Put two resistors in series to get the needed resistance 19,000 ohms (red,red,orange,gold) and 22,000 ohms (brown,white orange gold). 40,000 ohms will read at or around 28 degrees F. The two wires from the ambient temp switch go to the controller under the passenger seat, that is a convenient spot I chose to splice in. I am not sure how much of a discrepancy there can be between my 28F and actual outside temp before a dtc is set. I have only gotten to use this when the outside temp was 24F.
How ingenious! I'll be tacking this before next winter. Thanks so much.

Cheers
 

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Parts I bought to override erdtt. Radio shack; dpdt switch 2750663 $4.99, pc board 2760148 $2.49, resistor pack 2710312 $14.49 and some 22 gauge wire. Put two resistors in series to get the needed resistance 19,000 ohms (red,red,orange,gold) and 22,000 ohms (brown,white orange gold). 40,000 ohms will read at or around 28 degrees F. The two wires from the ambient temp switch go to the controller under the passenger seat, that is a convenient spot I chose to splice in. I am not sure how much of a discrepancy there can be between my 28F and actual outside temp before a dtc is set. I have only gotten to use this when the outside temp was 24F.
I like it. Can you describe how to identify the wire you splice into? Do you just install the switch such that this circuit is either left out or put in line based on position?
 

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I am also thinking about making a hold switch using the hood ajar circuit, being the engine turns on when the hood is open or thinks its open. I really did not want to alter my Volt, but Gm has let me down by not offering software updates for the erdtt issue that I do not think would take new hardware.
 

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I like it. Can you describe how to identify the wire you splice into? Do you just install the switch such that this circuit is either left out or put in line based on position?
Give me sometime, I will draw up a schematic, and have more details. Going out to wash my Volt.
 

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I am also thinking about making a hold switch using the hood ajar circuit, being the engine turns on when the hood is open or thinks its open. I really did not want to alter my Volt, but Gm has let me down by not offering software updates for the erdtt issue that I do not think would take new hardware.
I don't think that would work. When the hood is detected as being opened, the engine runs, but it does not actively try to maintain an energy buffer. I fact, I don't believe it puts any energy to the wheels or battery when running in this way.
 

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I don't think that would work. When the hood is detected as being opened, the engine runs, but it does not actively try to maintain an energy buffer. I fact, I don't believe it puts any energy to the wheels or battery when running in this way.
Here is what WopOnTour said about this.

To be fair, this was true for the original pre-release software. In fact this detail was even part of the Volt training materials provided to dealers. (ie will not charge by "hood open" input alone) But control strategies change for a myriad of reasons as it did here. Apparenty there's really very little incentive to change the decriptions in the owners manual as there's no scenario in which GM advises this behavior to be taken advantage of by the owner.
But knowing HOW it REALLY works doesnt hurt and there mght be some opportunity created to take advantage of that knowledge.
WOT
 

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Discussion Starter #16
I am not advocating anybody does this. Also has not been tested through a wide range of temps below 25f.
Thanks Regen. Your description and schematic is the type of answer I was hoping for when I asked the original question. Of course, making a modification like this is a bit scary. I wish GM would come through with a simple dealer procedure. I'd even pay for it.

Given that GM selected a lower setpoint of about 15F, might there be a reason (some protective action) why this value should be respected? If true, then you'd have to remember to throw the switch back at 15F or below to allow the control system to do its thing.
 

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There was a long thread back in May on exactly this topic - culminating in details how to perform a mod like this. But for some inexplicable reason...the thread was removed from the forum. However, I've been able to acquire much of the data. Will post some relavent service manual pics here.

2407258.jpg 2405937.jpg 2474736.jpg 684793.jpg 2387399.jpg
 

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Couple more pic.

It was confirmed the temp sensor is a thermister. There was a temperature/resistance curve provided...but unfortunately I don't have that. The suggestion was a 40kOhm resistor in series with the temp sensor. That's different than the parallel solution you've implemented.

I'd be concerned about the parallel implementation - when you switch over, if the vehicle is on, for a brief moment the Volt control circuitry will see open circuit rather than the thermister or the 40k. Dunno how it would react to that. I suppose depending how rapidly you switch, and how much bounce the switch has, the result might be somewhat variable from trial to trial.

I also have most of the text of the thread, but pretty much all of the useful data is contained in the pics. A bunch of the posts of the original thread revolved around comments of a particular user who seemed to be doing his best to put down anyone that would actually desire to change this aspect of Volt behavior. 'Nuff said.....

Ambient.jpg Misc.jpg
 

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Anyway, I've been seriously considering trying this mod for myself. But didn't want to be the first..... ;-)
I went as far as pulling up the carpet to look at the control module....but then decided I didn't want to be cutting wires on my baby.

I totally LOVE my Volt (and before I get jumped on for criticizing Volts, let it be clear I put a deposit down 1.5 years before available in Canada, and I believe I was the first Canadian country wide to have one parked in his driveway - that's how keen I was)....but....I think GM REALLY dropped the ball on this ERDTT implementation. And the clearly realized since the MY13 was changed. Boggles my mind a simple firmware change can't globally be offered to uses of pre-MY12, but rumour has it there's some kind of hardware issue that makes this not possible.
ERDTT, as gets discussed over and over again, is NOT for heating the battery. Good authority in this forum has indicated it's about having heat available for use warming the cabin. I think specifically heat available for clearing the windshield. I suppose perhaps a safety thing. GM maybe didn't want hyper-milers choosing not to use battery heat and thus driving along with a partially obscured wind screens since they were trying to save every electron possible. Not really sure. Never seen a 100% clear and complete justification why GM chose to take the option out of users hands and force the ICE to run just so there's warmth for the cabin.

I will say I like ERDTT when it's -20C (-4F) here in Ottawa...because under THAT circumstance I'm happy to use some gas, along wtih come electrons, to warm up the cabin as quickly as possible. But I FREQUENTLY (ie. sometimes 5 times on Sat) drive my daughters to competitive dance classes and drives me bonkers that each time I make that 10km trip, when it's -4C (ie. all the time in Ottawa winter!) I have to waste 0.5L of gas even though I have a totally full battery. Utterly ridiculous in THAT scenario to force the ICE on (vehicle warm from my garage and fully charged). As a user I'm all about choice. And I really wish the choice to use the ICE, or not, was more under my direct control.

All this has got me thinking again. Spring not far around the corner...but maybe I'll do this mod for next winter.

Interested in anyone else who has actually performed this mod...please post and share your experience.
Thanks!!
 

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I've been considering a mod like this, but haven't had the time to implement it. I was going to get a little fancier using a microcontroller with a digital pot device for the output. It would report "real" temps above 30 or 35 F and would offset temps by 10F below that (perhaps with a ramp in-between; something you could reverse in your head). So ERDTT would still run at 15F, like the 2013.
 
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