[Steverino]

With winter approaching and a relatively nice day, I decided to install my modified ambient outside air temperature sensor. It has a small 1/8W, 39k Ohm resister wrapped around the two sensor poles. This resistor tricks the sensor to see a higher temperature than actual. The result: the Volt always thinks it's about 40°F outside even if it's -10°F.

Why did I do this?

So my gas engine doesn't run 2-3 times on a short trip to a store or restaurant even though my battery is fully charged and the car interior is warm. This is called Engine Running Due to Temperature (ERDTT). GM decided that they would run the gas engine for you when it gets cold outside. Even if you don't want or need it to run. My 2011 initiates ERDTT when the outside temps hit 15°F or below (I think the 2019 allows the ERDTT to be set to -13°F).

With ERDTT, it doesn't matter if my car is already warm and cozy, it doesn't matter if I have enough battery to warm the cabin for my trip. Chevy decided it's going to run the engine anyway, wasting gas to create cabin heat that I don't need. Hence, the ERDTT defeat sensor.

This will be the second year I have used the modified sensor. The only downside is you won't know what the actual outside temperature is.

My install process is to drive the front tires up onto two, stacked 2" x 12" x 36" boards, one set of these "ramps" for each wheel. This raises the front nicely. Engage parking brake, chock the rear wheels.

Using my scissors jack under the front passenger lift point, I raised the car, but not all the way. Loosened the wheel lug nuts, raised the wheel off the wood ramp, removed the wheel. I placed a three-legged jack stand under the jacking point, lowered the scissors jack so the car was now resting on the three legged jack stand as well.

I removed the three 8MM bolts on the skid plate mounted to the underside of the engine area. Removed the 5, 7MM bolts holding the small air dam wing and the first 2 7MM bolts of the longer air dam. Removed the entire fender liner (#2T Torx bit and a small, flat bladed screw driver for to plastic pop rivets). Set aside the wheel liner (it includes the skid plate). Lots of access to the car's underside now. No fighting plastic pieces, scraping my wrists or working blind.

The black air temp sensor with blue connector is located above the 7th air dam bolt, and is press fit into the plastic housing that surrounds the front air intake louvers. I basically twisted it a bit and pulled it out. Using a small, flat bladed screwdriver I gently pried to long black clip running down one side of the sensor, releasing the sensor from it's blue connector. I was careful not to lose the gray, ribbed water/dirt seal.

Plugged in my resistor-equipped replacement. Reassembled.

Resistors https://www.amazon.com/NTE-Electronics-EW339-Flameproof-Tolerance/dp/B008UTY0RC
Related threads https://gm-volt.com/forum/showthread.php?127761-ERDTT-Modification-Options
https://gm-volt.com/forum/showthread.php?308145-Engine-running-during-winter

Will it void my warranty? No
Doesn't the battery need this for it's warming system? No
With this in, what if I want the engine to run? Put it in Hold or Mountain mode depending on your year.

 

[Lug_Nut]

CAT > OAT

I'm looking into a variation of this modification, and have searched the multitude of threads back to 2012 for an image of the Gen 1's Hybrid Powertrain Control Power Module 2 so as to identify the pair of wires that lead to the Outside Air Temperature (OAT) sensor. The text in some threads says reference the image, but there are no images, or the links are dead.

Does anyone have an image file they could post, or link to on a image hosting site, that shows the Gen 1's module and the wire bundle at the module?

The reason for this request is I'm investigating cutting the wires (from module pins 26 and 40) inside the cabin to install a plug and socket connection to a substitute Cabin Air Temperature (CAT) sensor. This would allow EDRTT when the cabin was cold (<25F, or optional <15F as in my 2014) and engine heat assist might be advantageous, but would inhibit engine operation once the cabin was up to a moderate temperature, such as from plugged-in preheating, despite cold out temperature.
The intent is to have the ERDT(L)T not run during my brief 10 mile each way commute when battery range is sufficient for the round trip.
I'd gladly trade the outside temp display, and lose the on-screen reminder that water freezes / thaws around 32F, for a limit to ERDTT. Having an accurate inside temperature display is a bonus.

 

[Bill Step]

just use the "MyHold app" it will keep the engine from running.

 

[Steverino]

I'm looking into a variation of this modification, and have searched the multitude of threads back to 2012 for an image of the Gen 1's Hybrid Powertrain Control Power Module 2 so as to identify the pair of wires that lead to the Outside Air Temperature (OAT) sensor. The text in some threads says reference the image, but there are no images, or the links are dead.

.

It's located under the front passenger seat.Which wires go to the air temp sensor? See this ERDTT Modification FAQ I have in the Newcomers forum: https://gm-volt.com/forum/showthread.php?127761-ERDTT-Modification-Options

just use the "MyHold app" it will keep the engine from running.

I recall some discussion on the pros and cons of this app. It is only temporary and must be used each time ERDTT starts?

 

[simplex]

About the warranty thing: The mechanic at the dealer saw this device and told me to remove it because if something fails later and they found you have modified this, the warranty could be voided.
Use precaution with this when you are still on warranty and going to the dealer for a repair that should be under warranty...
The good thing is, in the GEN2, it's easy to install/uninstall this in a few minutes without tools.
In Gen1 it's another story...

 

[G-PA]

Does anyone else appreciate the irony of the posters trying to defeat the ERDTT VS. those who can't get any heat in the cabin. With winter coming,I'm grateful for ERDTT.

 

[Steverino]

About the warranty thing: The mechanic at the dealer saw this device and told me to remove it because if something fails later and they found you have modified this, the warranty could be voided.
Use precaution with this when you are still on warranty and going to the dealer for a repair that should be under warranty...
The good thing is, in the GEN2, it's easy to install/uninstall this in a few minutes without tools.
In Gen1 it's another story...

Saw what device? Mine is the stock ambient air temperature sensor with a very small resistor wrapped around the two poles inside it. Unless they remove the air sensor (why?), and actually carefully look inside, they would see nothing.

If you had two side by side you would see nothing different. Again, you'd need to take it apart and look inside.

Unmodified sensor, modified sensor (there is normally a 2-wire connector plugged into the oval open end):

 

[Steverino]

Does anyone else appreciate the irony of the posters trying to defeat the ERDTT VS. those who can't get any heat in the cabin. With winter coming,I'm grateful for ERDTT.

The resistance cabin heater not working would have nothing to do with this defeat, but yes, I get it.

My resistance heater works fine, I get all the heat I need, no need to run the gas engine. ESPECIALLY on short trips with a full battery. Once the battery is half used, I can turn on Mountain Mode if I want gas-powered heat. Later years can use Hold mode at any time to do the same.

 

[Lug_Nut]

It's located under the front passenger seat.Which wires go to the air temp sensor? See this ERDTT Modification FAQ I have in the Newcomers forum: https://gm-volt.com/forum/showthread.php?127761-ERDTT-Modification-Options

I'm not adding a resistor to the current thermistor. I'm adding a second thermistor and a switch to select between the two sensors.
The factory front mounted thermistor will remain exactly where it is with no shunt resistor.
The wires to and from the factory sensor will be cut inside the cabin, wired to a switch, that will then select between the factory sensor up front or an identical sensor I add inside the cabin.

The FAQ link identifies the two wires by their number in the connector, but in which of the two connectors on that module?
Are the pin numbers in one connector not duplicated by the other connector, or does each connector have a "pin 26" inside?
Can I trust that the wire color code does not change at some conector / junction between the control module and the sensor at the bumper? If only one connector has a "pin 26" with a light blue with grey stripe wire, and the other connector's "pin 26" is a different color, that might help.
I've learned from 20 years of VW self-service that wire identification by insulation color alone is no assurance that the light blue with grey stripe at that end is the same circuit as the light blue with grey stripe at the other end.

 

[Steverino]

I'm not adding a resistor to the current thermistor. I'm adding a second thermistor and a switch to select between the two sensors.
The factory front mounted thermistor will remain exactly where it is with no shunt resistor.
The wires to and from the factory sensor will be cut inside the cabin, wired to a switch, that will then select between the factory sensor up front or an identical sensor I add inside the cabin.

The FAQ link identifies the two wires by their number in the connector, but in which of the two connectors on that module?
Are the pin numbers in one connector not duplicated by the other connector, or does each connector have a "pin 26" inside?
Can I trust that the wire color code does not change at some connector / junction between the control module and the sensor at the bumper? If only one connector has a "pin 26" with a light blue with grey stripe wire, and the other connector's "pin 26" is a different color, that might help.
I've learned from 20 years of VW self-service that wire identification by insulation color alone is no assurance that the light blue with grey stripe at that end is the same circuit as the light blue with grey stripe at the other end.

Yes, that's my idea of "ideal" as well, an in-cabin switch that effectively puts the resistor between the two wires as needed. ERDTT: On, Off.

Yes, would be nice to know the answers to the connector question. If you do find out, please let me know, but that's all the data on the wiring I have been able to gather to date. I'd love to see the pics and step by steps if you do this mod.

 

[Steverino]

I found some added info, maybe it will help?

x107 Forward Lamp Harness to Body Harness, p 12-644 R/Car 2011 Service Manual

Location: Engine compartment, right rear, at the top of the strut tower (ill. at 12-258)

Harness type Forward Lamp, (female) OEM Connector 13603186. Service Connector 13576550 40-way F 1.5/2.8 Series, Sealed (GY). Pin 6, BK/L-BU wire color. Circuit 61 Outside Ambient Temperature sensor Low Reference

Harness type Body, (male) OEM Connector 13603206. Service Connector 13576553 40-way M 1.5/2.8 Series, Sealed (GY). Pin 6, BK/L-BU wire color. Circuit 61 Outside Ambient Temperature sensor Low Reference

------------------------
Harness type Forward Lamp, (female) OEM Connector 13603186. Service Connector 13576550 40-way F 1.5/2.8 Series, Sealed (GY). Pin 7, L-BU/GY wire color. Circuit 636 Outside Ambient Temperature sensor Signal

Harness type Body, (male) OEM Connector 13603206. Service Connector 13576553 40-way M 1.5/2.8 Series, Sealed (GY). Pin 7, L-BU/GY wire color. Circuit 636 Outside Ambient Temperature sensor Signal

K114B Hybrid Powertrain Control Module 2 X1, p 12-565, 12-245 (pictures here https://gm-volt.com/forum/showthread.php?185202-hybrid-powertrain-control-module-2)

Location: passenger compartment, under passenger seat (12-329)

Fuse F33UA, 5A, X50A Fuse Block, Underhood (12-294, 12-292)

Harness type Body, (female) OEM Connector 34566-0703. Service Connector 13577545 80-way F mx123 Series, Sealed (BK with BU Terminal Position Assurance Lock).

Pin 26, L-BU/GY wire color. Circuit 636, Outside Ambient Temperature sensor Signal
Pin 40, BK/L-BU wire color. Circuit 61, Outside Ambient Temperature sensor Low Reference


B9 Ambient Air Temperature Sensor, p 12-439

Harness type Forward Lamp, (female) OEM Connector 13543521. Service Connector 12101856, 2-way F Metri-Pack 150 Series, Sealed (BK).

Pin A, L-BU/GY wire color. Circuit 636, Outside Ambient Temperature sensor Signal
Pin B, BK/L-BU wire color. Circuit 61 Outside Ambient Temperature sensor Low Reference

 

[Lug_Nut]

Sweet! That indicates that the OAT sensor wires continue the same wire insulation jacket colors through the lamp harness and body harness all the way to the control module.
The description of the module connector as "BK with BU lock" means that I don't need to inspect the module's GY color connector either.
As long as I can confirm the black connector has a blue with grey jacket at pin 26, and a black with light blue jacket at pin 40, I'm golden!
Thanks so much!

 

[Steverino]

Sweet! That indicates that the OAT sensor wires continue the same wire insulation jacket colors through the lamp harness and body harness all the way to the control module.
The description of the module connector as "BK with BU lock" means that I don't need to inspect the module's GY color connector either.
As long as I can confirm the black connector has a blue with grey jacket at pin 26, and a black with light blue jacket at pin 40, I'm golden!
Thanks so much!

It took me a while to track all that down, not being exactly sure what I was looking for.

Please posts pics and step-by-steps for your mod, Lug_Nut. It should be interesting and I think it'll be a first.

 

[2VoltFamily]

Will it void my warranty? No
Doesn't the battery need this for it's warming system? No
With this in, what if I want the engine to run? Put it in Hold or Mountain mode depending on your year.

Doesn't this affect cabin precondition? If it thinks it is warmer outside than it is would cabin precondition need to be set to HI?

 

[apoc69]

I went old school: Cardboard between my VoltScreen & the radiators intake. Just installed it so not sure it will do much of anything in the frigid Winnipeg winter but easy to un-do.

 

[2VoltFamily]

I went old school: Cardboard between my VoltScreen & the radiators intake. Just installed it so not sure it will do much of anything in the frigid Winnipeg winter but easy to un-do.

How would that keep ERDTT from coming on? If it is 0 degrees it is not going to change anything.

 

[Steverino]

I went old school: Cardboard between my VoltScreen & the radiators intake. Just installed it so not sure it will do much of anything in the frigid Winnipeg winter but easy to un-do.

If the Volt had a windspeed sensor that corrugated board might work. But it won't have any effect on an ambient air temperature sensor. It may help a bit when ERDTT goes on in that not as much cold air will be blowing over the engine coolant, so the coolant may stay warmer longer, slightly delaying the next ERDTT event.

 

[2VoltFamily]

It may help a bit when ERDTT goes on in that not as much cold air will be blowing over the engine coolant, so the coolant may stay warmer longer, slightly delaying the next ERDTT event.

Possibly, but my understanding is the ERDTT event only runs long enough to warm the coolant running to the heater core. The engine thermostat never opens to let the coolant go to the radiator during an ERDTT. Therefore, keeping air off the radiator will not affect cabin heating.

 

[hellsop]

Possibly, but my understanding is the ERDTT event only runs long enough to warm the coolant running to the heater core. The engine thermostat never opens to let the coolant go to the radiator during an ERDTT. Therefore, keeping air off the radiator will not affect cabin heating.

Letting it circulate in the radiator would waste the heat, and therefore be wasting fuel. Better to keep the temperature down to where the heater core alone is what's sapping heat from the engine.

There. We've solved the "Why doesn't ERDTT ever get the engine to operating temperature?" question and turned it into a fuel-saving virtue!

 

[jcanoe]

If you only use the gas engine for ERDTT and when EMM is active then the engine is never fully warmed up. That is not good for the engine oil, engine as any moisture in the crankcase is not driven out of the engine.