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Correct the MAF sensor also provides the engine fuel computer with air temp.

The question is: Is this temp sensor used only by the climate control system and the display for 'outside air' temp.
Does the Battery TMS use 'outside air temp' and does it share this same sensor? (Does anyone have access to the wiring diagram)

A set resistor replacing this sensor would keep the engine from coming on at low temps. (This would be used only seasonally. which came WAY too early this year ! )
The 'outside air temp' display would be wrong and you'd have to return it to stock before taking it to the dealer for any service.


I don't want my engine coming on. I'm fine with electric heat.

For example:
I experienced a situation today that is not good for the engine.
>Left the house, indicating 20° outside temp.
>Within 1/4 mile of my destination the engine came on, indicating 14° outside temp.
>I shut down the car because I had arrived at work.
>The engine did not even run 1 minute.

There is now moisture in my engine, engine oil and exhaust system,, just sitting there,,, until I finally run the engine again. ( which I will do on the way home to make sure the engine and oil get fully warmed up).

Dang it.... I was within 30 miles of 1000 miles without gas !!
I can live without the outside air temp display seasonally, in exchange for not having the gas burner come on !!

somms,
Thanks for all the research !
 

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No the car has a separate sensor for intake air temperature.
Yes, that is correct the Mass Airflow Sensor with Inlet Air Temperature Sensor is integrated into a single sensor attached to the AIR CLEANER ASSY.

BTW: For those who disconnect the Ambient Air Temp Sensor like I did to test, when you reconnect this sensor the center display will initially read -40F on the DIC. Just disregard this as it will take several minutes for the sensor to be recalibrated prior to reading an accurate temp again!;)

Pics below are how I installed a 1/2W 15k Ohms 5% resistor in place of the Ambient Air Temp Sensor in order to prevent unwanted engine runs this winter during our periods of inversion and below 15F temps here in the valley. After putting this resistor in, the center display now displays 58F and will not drop below this even when temp does fall. If I do decide that I want engine assisted heating, I can still manually turn engine on by putting the Volt into Mountain or Hold mode! Also dropped the Config setting from Very Cold (15F) back to Cold (35F) since this setting is now bypassed anyways. Probably leave this resistor in for the duration of the winter and will reinstall the actual sensor sometime in the spring. Just left the loose sensor in the glovebox for safekeeping!:D



 

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somms,

Thanks again for getting this ball rolling!
You have a workaround.
My only concern is the battery TMS and where it gets its temp sensing from.
This quote is from the following linked thread:
These passages permit the cells to be cooled or heated depending on operational requirements. The coolant inlet to the battery housing includes a debris filter, and a variable high voltage heating element that operates directly off the 360V Lithium Ion battery, and able to accurately heat the coolant when the battery cells are too cold. http://gm-volt.com/2010/12/09/the-chevrolet-volt-coolingheating-systems-explained/

How do you know your battery is happy?

The approach I may do is: parallel twin wires at the original temp sensor and run them into the cabin.
(This may be a be chore.) And have a pot to dial in a correction factor, always to a slightly higher temp, and only as it gets close the 15° 'Engine running' point. You can watch your adjustment on the display.
This would be much harder to conceal when taking the car in for service. I would rather use your approach but,,,
We have to find where the battery TMS gets its air temp sensing from.
 

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somms,

Thanks again for getting this ball rolling!
You have a workaround.
My only concern is the battery TMS and where it gets its temp sensing from.
This quote is from the following linked thread:
These passages permit the cells to be cooled or heated depending on operational requirements. The coolant inlet to the battery housing includes a debris filter, and a variable high voltage heating element that operates directly off the 360V Lithium Ion battery, and able to accurately heat the coolant when the battery cells are too cold. http://gm-volt.com/2010/12/09/the-chevrolet-volt-coolingheating-systems-explained/

How do you know your battery is happy?
My approach to the engine running due to low temperature is different. I just put a piece of cardboard on the lower grille and some transparent tape on the higher grille. This way, the temperature sensor is not exposed to the cold air directly. it works as now the temperature on the DIC is 2degC higher than the outdoor temperature and the engine kicks in 2 degC lower.

The temperature sensor for the battery is different. I have made extensive measurements (see http://gm-volt.com/forum/showthread.php?84778-Battery-thermal-management-Actual-measurements) and my piece of cardboard did not change the TMS behavior.
 

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Fredo,

I looked over your thread on TMS. You plot 'air temp' but we still don't know which temp sensor the TMS is using.
There are 2 that I know, the one provided by the MAF and the on up front that the temp display and 'ERDTT' uses.
Are there more? Which one were you plotting?

Your idea of blocking off the grill is not adequate to keep the ERDTT from running the engine when it's less than 15° F.
Why would it be warmer up there? The transaxle and inverter are making a little waste heat but any wind speed at all and that is gone.

I won't be using a pot to 'dial in' a temp slightly above 15° until I know for sure if this affects TMS.
 

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somms,

Thanks again for getting this ball rolling!
You have a workaround.
My only concern is the battery TMS and where it gets its temp sensing from.
This would be much harder to conceal when taking the car in for service. I would rather use your approach but,,,
We have to find where the battery TMS gets its air temp sensing from.

AFAIK, The battery pack has 16 temperature sensors. The temperature sensors are located on the top of the batteries. There are schematics in the Volt service manual that shows these temp sensors 1-16 to confirm this. I'm not concerned with trying to conceal the Ambient Air Temp Sensor since its primary function when it is cold is to display the current air temp on the Center console display which will force the ICE to run regardless if the cabin temp is already comfortable and the ICE was already previously running if it ever senses a resistance greater than the software ERDTLT threshold!;)
 

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Fredo,

I looked over your thread on TMS. You plot 'air temp' but we still don't know which temp sensor the TMS is using.
There are 2 that I know, the one provided by the MAF and the on up front that the temp display and 'ERDTT' uses.
Are there more? Which one were you plotting?

Your idea of blocking off the grill is not adequate to keep the ERDTT from running the engine when it's less than 15° F.
Why would it be warmer up there? The transaxle and inverter are making a little waste heat but any wind speed at all and that is gone.

I won't be using a pot to 'dial in' a temp slightly above 15° until I know for sure if this affects TMS.

Blocking the grille won't prevent ERDTT but will trigger it at a lower temperature. This is my second winter with the grilled blocked and I have never seen the ERDTT above 11°F so this is a 4 degree "saving" for a 5 minutes trick.

I have a short 15 minute commute. The temperature of the transxale jumps from 36 to 48°F and the power inverter from 32 to 48°F providing some heat to the radiator not so far from the sensor. In my logs, I have seen up to 54°F for the transaxle for longer trip with below freezing temperature.
 

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So you're saying the TMS does not really monitor ambient air?
It is only looking at the 16 battery cell temp sensors?
How does it decide to just run the 'radiator' fans or turn on the AC compressor also in hot situations?
I'm pretty sure I just had the fans on during hot weather charging last summer.

I am concerned about the air temp sensor because I don't want my engine to come on for 30 seconds at the end of my commute and then shut down with condensation everywhere. That's what happened to me a few days ago.

I can commute just fine with electric heat only.
I want to decide when I need 'ERDTT'.

I am just trying to figure out if 'adjusting' the ambient air temp sensor is messing with the TMS system.

Thanks for all your help, I have Torque running on a 7" tablet but don't log anything, just watch my many many gauges,, Bill
 

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The AC compressor function is to provide refrigerant flow in the AC refrigerant loop to help cool down the cabin, help dehumidify the air in a defrost mode and help maintain the battery temperature. Rather than a more typical pulley, the A/C compressor uses a 3-phase alternating current, high voltage electric motor to operate. It has an on-board inverter that takes High Voltage direct current from the vehicle's High Voltage Battery and inverts it to alternating current for the motor. The AC compressor shall be activated when any of the three following events occur:

• The customer pushes the AC button
• The HVAC control, in AUTO mode, requests the electric AC compressor on to help in cooling the cabin or removing moisture in the defrost mode
• The High Voltage Battery Thermal System requests the AC compressor on to help maintain the battery temperature

The Hybrid Powertrain control module 2 uses values from the A/C refrigerant pressure transducers, A/C refrigerant thermistor, duct temperature sensors, ambient air temperature sensor, passenger compartment temperature sensor, evaporator temperature sensor, battery cell temperature sensors, battery coolant temperature sensors and battery coolant pumps to determine the speed at which the compressor will operate. This speed request message is sent from the Hybrid/EV Powertrain Control Module 2 to the A/C compressor control module via serial data message.

The ambient air temp sensor is one of nine values used by the Hybrid Powertrain control module 2 in order to determine the speed at which the 3-phase AC compressor will operate if the Air Conditioning button is pushed, in AUTO mode to remove moisture in the defrost mode or High Voltage Battery Thermal System requests the AC compressor on to help maintain the battery temperature. This is why I plan on only using the bypass during the cold winter months and reinstalling the sensor before the summer months!;)
 

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All of this to prevent random condensation in the engine that will quickly evaporate on next run anyway? I suspect there will be very little condensation if any and in my mind, not running the engine with a bit of frequency might also be damaging equally or worse than condensation by letting seals get dry, cylinder walls end up with no oil on them, hard deposits forming and so on. All for the sake of burning a little bit of gas which in the long run is pretty insignificant to the overall cost of ownership. I don't mind running my ICE in the winter at all as I feel it is good for it. Also, I know that in two years I will certainly use up my oil life this way instead of pouring good oil down the drain. There are a lot of reasons to just not be worrying about it and let the engineering and technology in the volt manage it.
 

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All of this to prevent random condensation in the engine that will quickly evaporate on next run anyway? I suspect there will be very little condensation if any and in my mind, not running the engine with a bit of frequency might also be damaging equally or worse than condensation by letting seals get dry, cylinder walls end up with no oil on them, hard deposits forming and so on. All for the sake of burning a little bit of gas which in the long run is pretty insignificant to the overall cost of ownership. I don't mind running my ICE in the winter at all as I feel it is good for it. Also, I know that in two years I will certainly use up my oil life this way instead of pouring good oil down the drain. There are a lot of reasons to just not be worrying about it and let the engineering and technology in the volt manage it.
Exactly! I am a button push away from still having the "option" of turning on the ICE whenever I choose by either selecting Hold or Mountain mode on the fly. Now, the ICE is not being "forced" to run whenever the temp may drop slightly below a software threshold even though the cabin may already be nice and toasty which is rather silly and redundant!;)
 

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Exactly! I want the option of NOT running the gas burner when I don't want it.

It was not "random condensation". It was a worse case scenario of the engine coming on for the first time in maybe a month and it's 14°F and the engine ran for < 1 minute.
Can you imagine what the inside of the combustion chambers and the entire exhaust system looked like?

I had the option of running the engine for 30 mins. on the commute home and getting it warmed up thoroughly. I pressed HOLD.

Now I want a workaround to make sure that does not happen again.
 

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Wish there was a logical reason why GM didn't give us the option to disable engine running due to temperature
If we so choose. Seems rather silly to me to waste gas producing additional heat I don't need when I have plenty
electric range for my commute plus electric heat.
 

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Wish there was a logical reason why GM didn't give us the option to disable engine running due to temperature
If we so choose. Seems rather silly to me to waste gas producing additional heat I don't need when I have plenty
electric range for my commute plus electric heat.
Yes, I too am unclear on why they setup the car to auto-run the ICE when the temp goes below 35°F/26°F/15°F. What's the benefit to me or the car?

Perhaps it's a convenience idea that went too far ("they will like the extra cabin heat when it's x°F outside"), or not far enough ("nah, few will want a switch to turn it off").
 

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It's 20 degrees and the engine goes on so offer that I can't even drain my battery on my commute. Is there any way to override that?
Move to a warmer clime...:rolleyes:
 

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somms, thanks for the super useful resistance to temperature chart!

Instead of substituting a fixed resistor I am going to calculate a series or parallel resistor (with a switch) so my 2012 will act more like a 2013 and use ERDTT only below 15 deg. F (or maybe 10). On really cold days I see (feel) the benefit but it is pretty annoying to have it come on at 24 deg. F. So I think lowering the threshold (like the 2013 does) will work better for me, and will also give me a better idea of how cold it actually is outside (with a correction factor).
 

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somms, thanks for the super useful resistance to temperature chart!

Instead of substituting a fixed resistor I am going to calculate a series or parallel resistor (with a switch) so my 2012 will act more like a 2013 and use ERDTT only below 15 deg. F (or maybe 10). On really cold days I see (feel) the benefit but it is pretty annoying to have it come on at 24 deg. F. So I think lowering the threshold (like the 2013 does) will work better for me, and will also give me a better idea of how cold it actually is outside (with a correction factor).
Chart would be better if it were anywhere close to being accurate!:p

By the chart, 15Kohms should be @40F whereas the center console for my 2013 Volt is reading static 58F instead!;)

Maybe if I get a chance later I may experiment with various other Kohm resistors and report back what other values readback on the display. Keep in mind that the center console temperature display is NOT realtime as soon as the resistor or even the original sensor is plugged in. You will initially get the max -40F reading until the BCM consistently reads this value for several minutes. In my case, I installed the resistor at night and of course, the center console initially read -40F (and engaged the ICE immediately) but by the next morning it had registered at 58F where it has held at ever since. If you have no resistor or sensor attached and power on the Volt, the center console will display NO temperature value as well as the ICE engaging immediately upon power on.

You could get creative and put 2 10Kohm resistors in series for 20Kohm or 2 32Kohm resistors in parallel for 16Kohm resistance, ect. but I just wanted to keep it simple as possible and the way I have this installed, I am literally about a minute (1ea 9/32 screw away) from reconfiguring the original temp sensor back in if I really had to. The actual sensor will probably get reinstalled eventually in the spring!:)


Charging System Operation

The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
• Battery Sulphation Mode
• Normal Mode
Fuel Economy Mode
• Headlamp Mode
• Voltage Reduction Mode
• Plant Assembly Mode


Fuel Economy Mode

The BCM will enter Fuel Economy Mode when the ambient air temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is greater than -8 A but less than 5 A, and the battery state of charge is greater than or equal to 85%. Its targeted accessory power module set point voltage is the open circuit voltage of the battery and can be between 12.6-13.2 V. The BCM will exit this mode and enter Normal Mode when any of the conditions described above are present.

BTW: Keep in mind that you probably shouldn't pick a fixed resistance that reads back on the center console<32F since it may possibly throw you out (or in?) of Normal mode for 12V battery charging!?:confused:
 

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Man, this is getting complicated. Now it affects the 12V battery along with the HV battery???

So what about putting a resistor in parallel or series (it's early) with the original sensor to offset ambient temp up 10° or 20°?
This offset would be easy to figure if you want to know what the real outside air temp is from the display.
10° would work for me. Canucks would need more.
 

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Man, this is getting complicated. Now it affects the 12V battery along with the HV battery???

So what about putting a resistor in parallel or series (it's early) with the original sensor to offset ambient temp up 10° or 20°?
This offset would be easy to figure if you want to know what the real outside air temp is from the display.
10° would work for me. Canucks would need more.
Yes, that's exactly what I proposed. Ideally something that goes inline using the existing connector, and has a weatherproof bypass switch that makes turning it on and off easy at the start and end of the cold season. But I might try modding the existing piece first (but I haven't taken mine off yet so I don't know how feasible this is; maybe I'll do that today).
 
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