Hack achieved! ERDTT is now ERDTD (Engine Running Due To Driver)
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Thread: Hack achieved! ERDTT is now ERDTD (Engine Running Due To Driver)

  1. #1
    Join Date
    Sep 2016
    Location
    SW Michigan
    Posts
    17

    Cool Hack achieved! ERDTT is now ERDTD (Engine Running Due To Driver)

    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. 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.

  2. #2
    Join Date
    Sep 2016
    Location
    SW Michigan
    Posts
    17

    Default 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.

  3. #3
    Join Date
    Jul 2013
    Location
    North East USA
    Posts
    1,041

    Default

    Neat setup. I like this better than the "Ban ERDTT" hack.


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  6. #4
    Join Date
    Sep 2015
    Location
    North Carolina
    Posts
    1,641

    Default

    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.

  7. #5
    Join Date
    Jan 2011
    Location
    Illinois
    Posts
    15,290

    Default

    Yes, cabin control is the way to go. Would be nice to see pics of engine bay and firewall wiring, switch, etc.
    2011 Cyber Gray, Std Wheels, Black Leather/White Console, Bose, Nav, Htd Seats, Park Assist. Picked up May 2011
    B3320
    Best All Electric Miles: 54.2
    Lifetime: 85,558 miles, 125 MPG, Remaining Oil Life 38%
    Typical Commute: 60 miles
    30 day Stats: 966 miles, 108
    MPG, 62% Electric, 38% gas, Saved 33 gal., 31 kW-hr/100 miles
    Hidden Content Free Volt Manual here: Hidden Content

  8. #6
    Join Date
    Sep 2016
    Location
    SW Michigan
    Posts
    17

    Default

    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.

  9. #7
    Join Date
    Sep 2016
    Location
    SW Michigan
    Posts
    17

    Default

    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.

  10. #8
    Join Date
    Mar 2017
    Location
    Michigan
    Posts
    1

    Default

    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!

  11. #9
    Join Date
    Sep 2016
    Location
    SW Michigan
    Posts
    17

    Default

    Yes, 7500Ω resistor to make the car think it's warmer than 32 outside. Makes it think it's 42. Works great.
    Last edited by scoobie; 04-03-2017 at 06:05 PM.

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  13. #10
    Join Date
    Mar 2017
    Location
    VA
    Posts
    21

    Default

    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
    2017 Volt LT

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