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Discussion Starter #1 (Edited)
Hi everyone!

I bought my Volt a few months ago and where I live, it's finally cooled off enough to turn on the heat for the first time. Sure enough, it doesn't get hot in EV only mode, it's ice cold. I did some searching on the forums and ound a few things to look for:

The Problem
Before turning on the car: heat is set to HI, Fan Only mode ON, air power is OFF, auto defog OFF
Right after turning on car: heat is HI, turn to Comfort Mode ON, air power Level 1 (lowest), auto defog OFF

Attempted Diagnostics
Check Fuse #13 (Cabin Heater Pump) w/ ohmmeter: OK
Feel Heater Core Inlet Hose Under Dash: Unable to locate, can't diagnose
Check Both Coolant Levels Under Hood: OK

Observations
1. When turning on the above settings, Heat icon turns ON, cold icon turns ON, car makes a whirring buzzing sound from outside (hard to describe but I hear it when window is down) and car goes up to 6kW
2. Whirring buzzing sound from outside starts to taper down in volume every ~5 seconds, each time the kW reading drops by about 0.5-1kW
3. Whirring buzzing sound stops when car is around 1-2kW and Heat icon turns OFF, Cold icon is still ON
4. No hot air ever produced, instead ice cold air is produced

I hope this makes sense on what I tried! What do you all make of this? I've read up that it could be a few different problems:

  • Bad heater coolant pump
  • Bad coolant filter within the hose
  • Firmware update required
  • Clogged heater transfer core
  • Bad K10 Control Module

Any ideas on what the best next steps should be would be great! No DTC light is illuminated and the only scanner I have is a wifi one (not Bluetooth). I will attempt to connect it tomorrow to see if any codes are present, but am not sure that this scanner will be able to read the Volt (never tried it on this car before).

My background is that I have years of hobby repair and modding experience, so I'm comfortable working on cars. However, please let me know if any of this should be covered under some warranty/TSB/etc. so I don't have to spend my time looking. I would like to avoid unnecessary costs like dealer visits if possible.

Thanks again!
 

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Hi everyone!

I bought my Volt a few months ago and where I live, it's finally cooled off enough to turn on the heat for the first time. Sure enough, it doesn't get hot in EV only mode, it's ice cold. I did some searching on the forums and ound a few things to look for:

The Problem
Before turning on the car: heat is set to HI, Fan Only mode ON, air power is OFF, auto defog OFF
Right after turning on car: heat is HI, turn to Comfort Mode ON, air power Level 1 (lowest), auto defog OFF
Why?

Attempted Diagnostics
Check Fuse #13 (Cabin Heater Pump) w/ ohmmeter: OK
Feel Heater Core Inlet Hose Under Dash: Unable to locate, can't diagnose
Check Both Coolant Levels Under Hood: OK

Observations
1. When turning on the above settings, Heat icon turns ON, cold icon turns ON, car makes a whirring buzzing sound from outside (hard to describe but I hear it when window is down) and car goes up to 6kW
2. Whirring buzzing sound from outside starts to taper down in volume every ~5 seconds, each time the kW reading drops by about 0.5-1kW
3. Whirring buzzing sound stops when car is around 1-2kW and Heat icon turns OFF, Cold icon is still ON
4. No hot air ever produced, instead ice cold air is produced

I hope this makes sense on what I tried! What do you all make of this? I've read up that it could be a few different problems:

  • Bad heater coolant pump
  • Bad coolant filter within the hose
  • Firmware update required
  • Clogged heater transfer core
  • Bad K10 Control Module

Any ideas on what the best next steps should be would be great! No DTC light is illuminated and the only scanner I have is a wifi one (not Bluetooth). I will attempt to connect it tomorrow to see if any codes are present, but am not sure that this scanner will be able to read the Volt (never tried it on this car before).

My background is that I have years of hobby repair and modding experience, so I'm comfortable working on cars. However, please let me know if any of this should be covered under some warranty/TSB/etc. so I don't have to spend my time looking. I would like to avoid unnecessary costs like dealer visits if possible.
How much heat to expect to transfer away from a thermostatically controlled heater core with the fan off or at its lowest possible setting? The core's probably hot. Try blowing a bunch of air past it.
 

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Discussion Starter #3
Thanks for asking, I should have clarified. When I first discovered the problem it was on full blast. I tried again on another trip this morning and it was freezing cold the whole commute haha!

I didn't want to test again Saturday night on full blast since it is so stinking cold on full blast.
 

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Seems kinda common on Gen 1's … mine, as I recall, was the pump. I seem to recall it being in one of the rear fenders wells (not 100% sure though).
 

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If you are still within the 3/36 bumper to bumper warranty, it is likely covered (except for the obvious, like it was caused by a collision, etc.)

If the 3/36 has expired, you are probably still under the Voltec warranty. Some heating problems are not covered by this, but some can be, so it is worth asking.

Until you get it fixed, you might be able to get heat by running in hold mode.
 

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One other thing I didn't see listed which seems to probably be more likely is the heater coolant control valve. This isolates the heat circuit when the engine is off to circulate between the K10 module and the heater core. If it's stuck in the "ICE" mode, the coolant won't flow between the heater module (k10) and the core, but you will get heat with the engine on since it's stuck in the position to allow coolant to flow between the engine and heater core. This will be the control valve located just to the right of center along the firewall (drivers side) with 3 hoses attached to it. Since it seems you are getting power to the K10 as evident by the kW usage starting at 6, it would appear it is generating heat but unable to circulate to the heater core. I found mine had a plugged heater contamination filter (the inline filter) but that impacted both gas and EV heat, however if I turned the heater on for a few minutes, turned it off for a couple, then back on, I would get a small amount of heat for a moment which appeared to just be residual heat that warmed the water in the core through the convection process since the coolant wasn't flowing due to the plugged filter. If you have a VCX you can easily test that the coolant pump is operating as well as verify that the 3 way heater coolant control valve is operating. In my case, both functioned properly and removing the filter and cleaning the debris out fixed mine.
 

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Discussion Starter #7 (Edited)
Thanks everyone! I called a few Chevy dealers and they all want to charge $70 to diagnose the issue and then who knows how much they'll charge to fix it. I'm thinking about just do it myself.

Also yes, I can get heat in ICE hold mode. So sounds like the 3 way pump might be the issue?

Can someone tell me a bit more about the VCX module? Basic googling tells me it's a GDS tool, is that right? I have a GDS tool for my Kia and love it!

Any specific brands/models that you would recommend? It seems that VCX Nano seems to be the popular device choice for Chevy.

Thanks!
 

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The VCX nano definitely seems to be the preferred unit around here. I have one and found it invaluable when I diagnosed my heater as it gave control over the control valve and the auxiliary pump so I could test that the valve was in fact opening and closing as indicated and the pump was in fact operating. It also reads the heater core temperature which also gave additional confirmation that any sensors involved were reading correctly. I haven't yet bought a single VIN subscription since I haven't had to program any modules but just for diagnostics it's already paid for itself by allowing me to avoid a service visit.
 

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Discussion Starter #9
Awesome thanks! Did you need to pay for a GDS subscription or was the software included in the price? The GDS software that came with my Kia tool was part of the one time price and I only need to subscribe if I plan to do firmware updates, ECU flashing, etc.

If only I could use the same VCI tool for both cars... Haha!
 

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the VCX comes with the GM GDS software that runs through a virtual console. As for the subscription for updates, that was not included and I have yet to buy one since I haven't needed to perform anything that requires it. I can't imagine the VCI is any different though so you would likely be just buying the software to gain access to the GM functions.
 

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I'm probably going to go to the dealership this week because I have the same exact problem. I've had the car for about 2 years now and I believe about two weeks ago was the first time I turned the heater on in more than a year and same thing as you....just cold air. If I change it to "Hold" from EV only then I get hot air. Also sporadically the car will heat in EV mode but more than anything it will not. I will update here with whatever the dealership tells me is wrong and the fix.
 

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Discussion Starter #12
Awesome, thanks jimmy! I can't wait to hear what they say, and I'm on the prowl for one of those VCX nanos this month. Maybe Santa will be good to me! Haha
 
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