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Discussion Starter #1
What I wanted:
  • Normal operation when desired
  • Force off mode when making short trips below ERDTT temp.
  • Force on mode when making long trips (further than full charge) but still want SOME heat (ie: ~34°)

Well, this is exactly what I've got now. :D I've got 3 resistors I can choose from:
  • a fixed ~10500Ω which make it think it's 30° (lets call this resistor A)
  • the stock thermistor (lets call this resistor B)
  • a fixed ~9500Ω which make it think it's 34° (lets call this resistor C)

I ran a pair of wires from the connector that plugs into the stock thermistor (I'm calling this the ECM wires) to the passenger compartment. I also ran a pair of wires from the stock thermistor into the passenger compartment. The ECM wires go to the input side of a DP3T switch. The middle output goes to the stock thermistor wires, the left output is bridged by the A resistor, and the right output is bridged by the C resistor.
Now if I want the car to be in "auto" mode, I choose the middle position. If I want to force ERDTT off, I choose the left position, which forces ERDTT off, REGARDLESS of outside temp (car thinks it's 34°). If I want ERDTT to run, even if it's ABOVE 32°, I choose the right position (car thinks it's 30°).
What's even better is that when running in "auto" mode, if I'm near my destination, I move the switch to the left position so the ICE won't cycle back on just as I'm pulling into my parking spot (this has happened more than once). Unfortunately, this is the one tidbit that doesn't work (yet). Apparently, once ERDTT is engaged, it won't give up if the temp only rises to 34°. I need to pick a different resistor value to make it think it's warmer (I know it will give up if temp is 42°). 42° is my next target value, and I'll update this thread when I have a chance to figure out that value. I know a resistor value that will make it think it's 60°, but I don't want to swing too far from reality because the car is too smart. I had a value that gave 119°, but that threw a DTC that indicated the refrigerant was low (it wasn't, but at 119°, the static pressure of the refrigerant should have been higher, but it wasn't because it was really only ~50°. I'm speculating on this last part, but there's also no reason to stray too far from the 32° trigger temp.
Oh, and I also used 'stock' connectors to connect to the thermistor and the ECM wires. I'll post those part numbers next.
 

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Discussion Starter #2
Parts list for connectors

To make the end that connects to the thermistor:
  • 1-1718643-1
  • 1452665-1
  • 967067-1

To make the end that connects to the ECM wires:
  • 1-1703498-1
  • 1718758-1
  • 967067-2

I think the wire seal parts are the same except for the color... Obviously color doesn't matter.
I used 20awg stranded. Everything clicks in place like it belongs there.
 

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That is a great way to implement the hack. I am sure many would be interested in buying a kit like that if it were available, rather than gathering parts and soldering it themselves.
 

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Yes, cabin control is the way to go. Would be nice to see pics of engine bay and firewall wiring, switch, etc.
 

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Discussion Starter #6
The wiring is definitely in "prototype" stages still. Finding a route through the firewall has been impossible so far in this weather. I did manage to get from the engine compartment to behind the grill, though I thought this would be the easiest part. It's not. It's well sealed save for the shutters in front of the condenser.
 

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Discussion Starter #7
Some minor adjustments needed. The 9500Ω resistor needs a lower value to make it think it's warmer than 34°. Here's why. Once ERDTT is engaged (sensed temp drops below 32°), it won't 'disengage' when the temp is 34°. I know 41° is high enough (was 41° the day I tried this). Now off to find a resistor to add in parallel to make the car think it's ~40°.
 

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Hey scoobie. Have you figured out the right set of resistors? I'm interested in doing the same thing my 2017. Having ERDTT for a 10 mile trip when I have more than enough charge drives me crazy!
 

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The only thing I would worry about is if GM used that temperature measurement as part of the plausibility diagnostics for other temperature transducers. So if you get some weird plausibility or rationality errors for a temp sensor, you'll likely know the cause.

Keith
 

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Living in a tropical paradise every day of the year means that a Volt sold here never needs to run the engine for heating. Another benefir is that the battery will be more efficient and deliver more range than the EPA rating. But GM hasn't permitted any local dealer to sell the Volt or Bolt EV.
 

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Discussion Starter #12
The only thing I would worry about is if GM used that temperature measurement as part of the plausibility diagnostics for other temperature transducers. So if you get some weird plausibility or rationality errors for a temp sensor, you'll likely know the cause.

Keith
I mentioned that in the first post (car thought refrigerant was low), but with my current chosen values of 30° and 42°, so far, no problems.
 

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Can I get a description on a long trip with "force on"? I assume this isn't a summer replacement for "hold mode" for 2011, 2012 MY Volts that didn't have hold?

In other words, the engine starts initially, but how long does it stay on? Does it cycle on/off after that?

Thanks.
 

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Discussion Starter #14
I just used the "force on" mode last week. It was 34°F outside, and my total days journey was going to be 71 miles. I can't make that in pure electric mode with the heat on, and I wanted heat. So, "force on", makes the ICE run (at about a 6kw output IIRC) until the coolant temp reaches about 140°F. Then the ICE shuts down until the coolant temp falls below 120°F. It cycles between these two temps, giving you 6kw and heat while it's doing it.
 

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As I suspected, use it as a means of early cabin heating for a trip.

Thanks.
 

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Made the same modification for my 2012 and I am really happy! In my case, I used a DPDT switch because all I want is disabling ERDTT on demand with a fixed resistance to the limit of temperature ERDTT start (-4C in my case) to be closer to the outside temperature for the climate control to behave "correctly". This way, it's better than the parallel resistance that offset the temperature too much when it's cold. Connected a 4 wires cable from sensor and ECM to a switch located just behind the passenger headlight.

The only thing missing to be perfect is if I was able to put the switch inside the car. The wire is long enough to go inside on the passenger side but I really don't know where to pass it. Maybe the glove compartment where the cabin filter is... Maybe later I will build a homemade device which read the outside temperature from the sensor, display it and toggle the ERDTT at the temperature I want just like GM must have done it from the beginning :)

Anyway, if anyone can help me to find a place to pass this wire inside, it will be really appreciated. Thanks.
 

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Made the same modification for my 2012 and I am really happy! In my case, I used a DPDT switch because all I want is disabling ERDTT on demand with a fixed resistance to the limit of temperature ERDTT start (-4C in my case) to be closer to the outside temperature for the climate control to behave "correctly". This way, it's better than the parallel resistance that offset the temperature too much when it's cold. Connected a 4 wires cable from sensor and ECM to a switch located just behind the passenger headlight.

The only thing missing to be perfect is if I was able to put the switch inside the car. The wire is long enough to go inside on the passenger side but I really don't know where to pass it. Maybe the glove compartment where the cabin filter is... Maybe later I will build a homemade device which read the outside temperature from the sensor, display it and toggle the ERDTT at the temperature I want just like GM must have done it from the beginning :)

Anyway, if anyone can help me to find a place to pass this wire inside, it will be really appreciated. Thanks.
Would a RF remote controlled relay work? There are versions that operate off of 12 VDC for automotive applications.

https://www.amazon.com/s/?ie=UTF8&k...qmt=b&hvbmt=bb&hvdev=m&ref=pd_sl_3iisr8h45g_b
 

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Some minor adjustments needed. The 9500Ω resistor needs a lower value to make it think it's warmer than 34°. Here's why. Once ERDTT is engaged (sensed temp drops below 32°), it won't 'disengage' when the temp is 34°. I know 41° is high enough (was 41° the day I tried this). Now off to find a resistor to add in parallel to make the car think it's ~40°.
couple Honeywell d53c110k might speed it up for you
 

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Living in a tropical paradise every day of the year means that a Volt sold here never needs to run the engine for heating. Another benefir is that the battery will be more efficient and deliver more range than the EPA rating. But GM hasn't permitted any local dealer to sell the Volt or Bolt EV.
Raymondjram - Tell the dealer you won't be needing the heated seats or steering wheel either. ;-)
 
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