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The seller, Jason, has been a member of the GM-Volt forum for a very long time and came out with the original ERDTT defeat kit for the Gen 1 Volt for those who do not want to make their own. They appear well thought out and constructed, though I do not have one. I made my own with a sensor and resistor. Of course that requires seasonal removal, something that at least on of Jason's solutions addresses with a simple switch.

We have a handful of non-commercial members who sell home-made items for the Volt including WOT sensors, air intake grills, charge handle cozy's that block winter ice/snow buildup in the charge port, rear cargo shelf, inverters to convert the Volt into an emergency AC power supply are just a few.

This is different than commercial businesses like car dealers, etc., and we give them a pass. So no, this post will not be treated as spam.

One thing I would like to encourage is fo all members to post their car make, model and year in their signature.
 

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The seller, Jason, has been a member of the GM-Volt forum for a very long time and came out with the original ERDTT defeat kit for the Gen 1 Volt for those who do not want to make their own. They appear well thought out and constructed, though I do not have one. I made my own with a sensor and resistor.
What resistance did you add to the sensor? 47k ohm?
 

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What resistance did you add to the sensor? 47k ohm?
39k Ohm. 1/8 watt. $5/pack of 6 Amazon. Outside temp sees high 49°F. No ERDTT last winter or this winter which is exactly what I was going for. Mines not fancy, just an OEM sensor with the resistor wrapped around the two sensor prongs. It is a pain to install and remove which is why Jason's switch solution is nicer.
 

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What temperature is displayed on the dash when it kicks on? Does it have any effect on auto defrost or anything else besides ERDTT?
 

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What temperature is displayed on the dash when it kicks on? Does it have any effect on auto defrost or anything else besides ERDTT?
It doesnt "kick in", instead it continually gives a false, higher temperature reading. My dash temp display is always in the 40's while the modified sensor is in. I haven't seen any affect on defrosting, but I normally use manual defrost.

How easy of an install is this? You mentioned switch, I'm assuming it's on the unit your installing correct?
Mine has no switch, mines always on. Then again, I didn't spend $50-$75, I spent under $10. If you want a switchable mod, then get joesonvolt's very nice unit off ebay. His has the added advantage of install once and you are done. Mine is a seasonal install and removal.

For my approach, I recommend getting a second sensor for $6 to add the resistor too.

You spiral wrap the resistor wires around the two pins of the sensor, one resistor wire per sensor pin (doesn't matter which is which).
You end up with spiral resistor spiral like this
@-•[email protected]
The pins are small, and so is the resistor wire. One way to do this is to use a nail of a slightly smaller diameter than the sensor pins, wrap the resistor wire in a tight spiral around the nail shaft like making a spring. Slide off the nail and slide/push onto the sensor pin. No need to solder, just push the coiled wires and resistor all the way to the bottom of the the connector cavity. Now replace the original sensor with the modified one.

I do this in Nov/Dec while the weather is still relatively warm. and then remove in April or so.
 

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My install cost me around $25 including a switch, but that includes $5 in shipping from Mouser and overly expensive waterproof switches I bought from Amazon (I likely could've purchased them from Mouser for a lot less). All you need is:

The connector housings (1 of each):

The pins and sockets (you need 2 of each, but order extras in case you mess up):

The wire seals (4 of each):

Waterproof switch (below is the one I used, but I'm sure there are cheaper options available)

Appropriate wire (OD of insulation must be 1.4-1.9mm, diameter of wire conductor must be 0.5-0.75mm). I found that wires I cut from the molex connectors on an old computer power supply were the perfect size.

Appropriate resistor. I used a 22kohm resistor, which I calculated should raise a temperature of -40F up to 16F.*

There is a data sheet with instructions on assembling the connectors at http://www.te.com/content/dam/te-co...bal/mcon-interconnection-system-1308070-4.pdf

Wire up the connectors, switch, and resistor as shown below, using waterproof heat shrink around any solder joints (surprisingly, the Hyper Tough heat shrink from Walmart has an inner glue lining to make waterproof connections):

OAT Bypass diagram.jpg

Bundle the wires together with waterproof tape, install between the OAT sensor and the cable leading to it, and zip tie the switch somewhere convenient (I attached it to the top side of the bar between the openings under the nose of the car, so I can reach under the car to activate it).

*Someone else posted a bunch of values they measured from their Gen2 sensor, and I did a trinomial curve fitting in Excel. According to the curve, a temperature of -40F corresponds to a resistance of 65,536 ohms, which makes sense as that is the largest value that a 16-bit variable can hold and -40 is the temperature that the car reports when the sensor is missing. In any case, a 65,536ohm resistor in parallel with a 22kohm resistor gives an equivalent resistance of 16.5kohm, which the car reads as 16F. If you want to raise the temperature higher, use a smaller resistor (e.g. if you want to accommodate the coldest-ever temperature in the US of -70F, use a 19.2kohm or smaller resistor.
 

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My install cost me around $25 including a switch, but that includes $5 in shipping from Mouser and overly expensive waterproof switches I bought from Amazon (I likely could've purchased them from Mouser for a lot less).
Awesome, thanks for the details, zanhecht. I may eventually make one of these, but with work and other projects, well, someday! :)
 
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