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Discussion Starter · #1 ·
I finally got to performing the ERDTT (engine run due to (low) temperature) defeat on my '14 Gen 1 Volt.
I bought the Volt for its ability to run on battery until depleted to its low state of charge limit, and then switch to electric power produced by its on-board generator. Discovering that low temperature will cause the combustion generator to start first was not something I was willing to tolerate. The numerous ERDTT work-arounds that others have used had additional results (side effects) that I didn't want. I devised a plan to make an ERDTT by-pass / defeat that would satisfy me. This thread is what I did.

I purchased a sensor, sensor pigtail and some 2 pole quick connectors.

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The controller is located under the passenger (right side) front seat on left hand drive cars. Possibly under driver's seat on RHD Ampera. The carpet is pre-cut for access.

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Seat removal allows for much easier access. Slide the seat forward to allow access to the two Torx screws at the rear of the seat rails. The outboard screw has a plastic cover over it. Press/slide the cover forward to permit unclipping the forward edge of the cover, lift the forward edge slightly to keep the clip clear, then slide the cover rearward to unclip the longer rear clip. Now the outboard Torx screw is accessible. The Torx bit is slightly larger than a T50. My T50 worked acceptably. There was a lot of thread lock and I had to fight the screws all the way out.

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Discussion Starter · #2 · (Edited)
Set the seatback to as vertical a position, and the seat bottom to as low a position as possible. Tip the seatback forward enough to lift the rear seat rail locating pins out of the floor. Keep the rear pins clear of their holes and slide the rails and seat as an assembly back enough to clear the rail's forward hooks from their slots in the floor. The whole seat and rail can be moved back and out of the way for clearance to the controller and connectors.

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The carpet over the controller can folded / hinged up to view the unit and connectors. The outside temperature sensor is connected through two wires in the "blue" connector. Slide the orange lock on the connector towards the front of the car. Press down on the latch release (just forward of where the unlocked orange lock has been positioned), and lift the latch.

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Airsoft gun Airsoft Trigger


I found there wasn't enough clearance to completely release the blue connector because the latch couldn't rotate over enough due to carpet interference. I unclipped the controller from its mounting bracket and pulled the whole unit up to get the connector completely off. Note that the connector insert colors of blue and grey are obvious when they are unplugged, even though the latch covers are both black.

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Discussion Starter · #3 · (Edited)
The cover can be unclipped and removed for access to, and color identification of, the wires. I did this step to assure myself that the color coded wires I thought I wanted actually matched the pin locations. The cover releases are seen near the tip of my thumb and the other near the tip of my ring finger.

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I segregated the sensor signal wire (light blue and the grey stripe, pin 26) and the sensor reference wire (black with light blue stripe, pin 40) from the others in the connector. Note that there is very little difference between the light blue and the grey stripe colors on sensor signal wire to pin 26. The wire looks at first to be only one color.

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I got my cutters, and rechecked a third time before snipping these two.
 

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Discussion Starter · #4 · (Edited)
There's no turning back now!

I stripped back the insulation on the four ends of my pair of cut wires and installed them into the mating halves of a two pole connector. The connectors had one pole with a black mark so I used that pole for the black with blue stripe reference wire. The unmarked pole received the light blue with grey stripe wire.

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I plugged the two ends together, reattached the controller to the grey and the blue connectors and performed a system check, to confirm the outside air temp sensor was still functional. All OK! (whew!).

I had concerns about my substitute sensor connection if the sensors were polarity sensitive. I had checked the factory outside sensor and noted the black wire location on that sensor. I made sure to connect my replacement temp sensor with the same location to a second two pole connector and inserted the other lead from the replacement to the remaining location of the two pole connector.

I then unplugged the first two pole connector to disconnect the outside sensor and plugged in my substitute sensor and performed another system check.

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Still good! I tucked the controller back into it's mounting bracket, left the substitute sensor on top of the carpet access, reinstalled the passenger's seat, and went for a coffee with the heater cranked up. The temperature display slowly climbed through the trip. When I got home the display was showing 45F (on the floor under the seat) while the thermometer at home was still showing just below freezing.

Later installments will (may?) show the installation of an ON-OFF-ON switch to select between the outside sensor and my added inside sensor.
Or I may just leave it set up as it is now.
 

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Looking forward to the next chapter :). BTW, listing the part numbers, where purchased and price will be helpful for others. Oh, those Torx bolts need to be torqued 45 nM (33 lb ft) when re-installing.
 

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Discussion Starter · #6 · (Edited)
The first photo in post 1 can be used to identify the part numbers and the vendor that I chose to use.
I could have sourced the items for less, but wanted to use vendors that nearly anyone would have local to them if they wished to exactly duplicate my choices. There is ample information from which to select alternatives if that suits.

Were I to do this again, I'd have cut the wires further away from the connector. I barely left enough for the two pole plug half to clear the connector's strain relief (see post 4, last image).
 

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The first photo in post 1 can be used to identify the part numbers and the vendor that I chose to use.
I could have sourced the items for less, but wanted to use vendors that nearly anyone would have local to them if they wished to exactly duplicate my choices. There is ample information from which to select alternatives if that suits.

Were I to do this again, I'd have cut the wires further away from the connector. I barely left enough for the two pole plug half to clear the connector's strain relief (see post 4, last image).
Part number for the new green sensor male connector?

Yes, a remote switch under the dash could be handy.

But even without that, being able to add the defeat sensor under the passenger seat by (now) simply unplugging the wire coming from the front air intake sensor and plugging in the defeat sensor sure beats doing it in the front bumper air intake grill.

Thanks for posting the pics and steps, Lug Nut!
 

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Discussion Starter · #8 ·
I used:
ambient air temperature sensor: Duralast SU2835, AutoZone item #184248, $9.99
connector pigtail: Duralast 444, AutoZone item #349737, $17.99
plug connector: Ideal model 102, Lowe's item# 540475, $4.98

I have the selector switch but will won't bother listing that until (meaning: unless) I actually install it.

The modification I performed appears to do what I want.
1) prevent ERDTT when the cabin is already pre-warmed above the ERDTT initiation temperature
2) allow ERDTT if the cabin is colder than the initiation temperature
3) keeps the temperature display accurate, even if it is now reading the inside, not the outside, temperature

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That is a great mod.

Forgive me for posting off topic, but the color of your center stack trim (surrounding the center screen) looks coppery brown in post #8. I have not seen that color before. Is that a normal color option? Or maybe the photo just has an odd color balance?
 

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That is a great mod.

Forgive me for posting off topic, but the color of your center stack trim (surrounding the center screen) looks coppery brown in post #8. I have not seen that color before. Is that a normal color option? Or maybe the photo just has an odd color balance?
Looks "woodgrain" to me :D
 

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Discussion Starter · #12 · (Edited)
I don't get why this bugs people. It runs for like 5 minutes at the most.
It is generally understood that one of the worst things to do to an ICE is to start it when the engine is cold. I happen to believe that as well. If I can avoid starting the engine I will. The purported reason for ERDTT is to assist the defrost. I have the car plugged into the grid and pre-heated, windshield defrosted, before I get in to leave in the morning. My commute is short enough that I can make the round trip on battery, even with the diminished winter range. Having the engine run in my circumstance is detrimental.


That is a great mod.

Forgive me for posting off topic, but the color of your center stack trim (surrounding the center screen) looks coppery brown in post #8. I have not seen that color before. Is that a normal color option? Or maybe the photo just has an odd color balance?
The white balance is off a bit. It was 4:30 and sunset this far east in the time zone so the reds and yellows were less prevalent than the blues, but not dark enough for camera auto-flash. The yellowish light of the dome lamp appears to be more pronounced and makes the silver/grey look brownish.

I wired up my switch with the same connectors to permit quick install.

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The switch is installed.

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I can reach the switch (Cambridge Resources item SW12932, purchased from AutoZone, $9.99) from the driver's seat with the passenger's seat slid back, but it is otherwise semi-protected from inadvertent change.

Note: I could have sourced the items I purchased for less, but I wanted to demonstrate that others that wanted to perform the same modification could buy items "off-the-shelf" locally and do the same work in an afternoon.
I spent $40, a few hours time, and have absolutely no pretense that I may ever recoup the expense from fuel savings, but I have successfully eliminated one of the annoyances I have with the car.

My wife, the dog trainer, no longer asks if I'm "marking my territory" when I fix something that isn't really quite broken.
 

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Discussion Starter · #13 ·
Not so fast, Grasshopper... I've uncovered an issue that makes my hack much less effective.

The temperature sensor in the cabin does not appear to react to changes in temperature until some amount of time after the car has been driving. The display shows the temperature when the car is 'started', and then that display remains static, even though the cabin has been warmed, for an unknown period with the car stationary. I could get response only after driving about a 1/2 mile.
That delay in updating the displayed temperature means that the display could continue to show an initial temperature of less than the ERDTT threshold, even though the interior cabin had been pre-heated while plugged in. In that case the engine run would initiate as soon as the umbilical to the house was disconnected.

Until I sort out what and why this condition exists, I have replaced the variable resitance sensor in the cabin with a fixed, 18,000 ohm resistor that produces a fixed "53 F" display when the selector switch is in the "interior" position.
 

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I've had my cheap 1/4 watt resistor perma installed into my Gen1 for now the 7th year (2012-2019) w/o any issue and no fuel-wasting useless ERDTT runs for those several years!:rolleyes:
 

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Instead of having to buy an entirely different vehicle my solution consisted of buying a simple resistor for 35cents!:p
This has been my solution as well, but I like seeing the outside temps, so I replace my resistor-modded sensor with the original in the spring when the ERDTT danger has passed. But combining that modded sensor with a switch in the cabin that enables me to use either the air intake mounted sensor OR the modded sensor inside the cabin seems ideal.
 

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Discussion Starter · #18 ·
Learn from your mistakes. Better yet, learn from someone elses' mistakes.
Learn from mine.

I also thought it ideal: A user selectable choice of two ACCURATE temperatures, and inhibition of ERDTT. I'd still like to find out why the temperature update is delayed. Until then I have a user selectable choice of either the accurate outside temperature with ERDTT available, or of a fixed nonsense display value and elimination of ERDTT.
 

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I have a user selectable choice of either the accurate outside temperature with ERDTT available, or of a fixed nonsense display value and elimination of ERDTT.
That works for me. My outside air temp reads in the high 40's or 50's regardless of the outside freeze. The difference is, I have to crawl under the front of the cars and dismantle a bunch of plastic when I want to re-install the normal sensor. Your mod let's you do it with a convenient switch.

Did you add the resistor to the stock sensor used under the seat?
 

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variation on a theme

Interesting mod lug_nut, and it tempted me, but...

Background: My 2014 lost electric cabin heat a few days ago. Perused the forums here, and both the number of failure modes and reported repair costs for some of them were disheartening. And to top it off, the ambient temp during those days was hovering just *above* the ERDTT "cold" Config setting (35F). FWIW, the only time I normally use any gas is the occasional 'road trip' and when ERDTT triggers below the "very cold" Config (15F).

I tried 'Hold mode' to get some heat, but it was clumsy for my short commutes, and doesn't help at all with remote start pre-heating. Used the 'start car / pop hood latch' trick to run engine for morning 'pre-heat' but it's also clumsy.

Pondering my options, I decided to temporarily hack the OAT sensor so I could take my time on the electric heat issue. My idea was to replace the sensor with a resistor that would report a temp between the two Config set points. Thus, I could turn ERDTT off by selecting "Cold" or on by selecting "Very Cold" Config option.

Again turning to these forums, I saw almost everybody focusing on the rather inaccessible connector behind the grill / fender. YUCK. Using the leaked / ripped 2012 service manual pdf I traced the circuit from there to X107 in the engine compartment and then to HPCM2 X1 under the passenger seat.

Compliments again to lug_nut for the excellent write-up on accessing the OAT sensor wires off HPCM2 X1, but the need to remove the seat (plus having the heated seat option in my Volt) ruled that out for me. That left X107 in the engine compartment. It's easily accessible, the wire bundle is fairly small, and pulling it (and X105 beside it) gives plenty of slack. The only remaining decisions were how to physically wire my mod up, and what resistor size to use.

Looking through my various bins and drawers of electronics stuff (I'm a licensed ham, and also dabble building / fixing stuff) I came across some telephone wiring splices - neat little plastic thingies with gel inside you push 2 or 3 wires into and press to make electrical contact. Not something I'd want to use long term in the engine compartment, but it should do until I get the root problem figured out.

So, what resistor to use? That 2012 SM pdf has an 8 entry table in it (that has also been posted in these forums) that shows temp vs resistance for the OAT sensor. And there were also a couple references here to a data sheet and a 44034 model number. HOWEVER, there were also some random posts of "I used resistor X and got temp Y" that DON'T line up with those tables. For example, lug_nut reported 18K gave him 53F above, and somms reported 15K gave him 58F.

Something fishy going on :confused: I collected several reports like above, and examining the referenced data sheet, it seems they 'fit' the table for "44006/44031" better. And if I'm reading the table headings in the data sheet right the '44006' has Black body / Blue end. Hmmm... Ok, midpoint between "Cold" and "Very Cold" would be 25F or approx. -4C, which for the 44006 would be 35.57K.

Blast it - I didn't have *any* thirty-k-ish resistors. Ended up using a pair of 74K resistors in parallel yielding 37K which, at the end of the whole process, gave me 29F. Higher than my target, and off some from the 44006 table (which says 37K should give 23F) but still safely between the two config set points. Hurray! :D

OK, I will post pics and commentary in a follow up post. Promise!

In the meantime I need help with an unanticipated problem. I now have a "Service High Voltage Charging System" message, check engine light, and the car won't charge from the charge cord (but it *will* from the engine). Looking back on it, pulling X105 in addition to X107, while making the process physically easier, may not have been the best idea when you look at the signals it carries. Stuff like:
Code:
High-Voltage Interlock Loop Signal 
High-Voltage Energy Management Communication Enable
CAN Bus Serial Data
High Speed GMLAN Serial Data
X107 is mostly sensors and control lines, so I doubt that's the cause. But that's not relevant at this point.

How do I clear this code? I just had an oil change and 'PM' visit about 6 weeks ago so (other than the recent electric heat issue) I'm pretty sure the car just got confused. I don't have any OBD dongles. Will a trip to an Autozone (or equivalent) be fruitful? I know they will generate reports and clear 'check engine' lights for free, but for the Volt?

Suggestions?
 
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