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How To Make Heated Seats Hotter

37K views 104 replies 28 participants last post by  Rainne 
#1 · (Edited)
NOTE: Always disconnect the 12V battery for awhile before messing with seat connectors due to airbags in the seats...

One of my grips with the Bolt used to be due to the pathetic amount of "heat" the "heated seats" would create. The heated steering wheel is great and will get up to ~120F, which will add heat into the body. The OEM Bolt seats would not even get above body temp, so they don't really "add" warmth to the occupants. And the amount of heat was far less than any of my other vehicles with heated seats.

I gripped about it and posted infrared measurements in this old thread where the temp gun was showing a max of 95/96 F on the "high" setting: https://www.chevybolt.org/forum/226-interior/30687-heated-seats-seat-covers.html

The reason GM and others are going to lower temp heat levels has to do with lawsuits against auto makers where people have sued, and won, for damaging their skin from heated seats getting "too hot" and occupants not taking precautions to make sure they don't hurt themselves. The Nanny State wins again and we have to dumb things down for everyone else...

There are lots of online rants about GM's newer models having pathetic heat output from their "heated seats". This was confirmed by multiple calls to local chevy dealers who confirmed the lack of significant heat output on newer models, and I was told there was no way to calibrate the heat level with software intervention.

So, this weekend I did some ******* Engineering and hacked/modified the seat heater control module to do my own calibration of the driver seat heat level. I am happy to report that this relatively simple modification (if you can cut and solder) will raise the seat heating output above body temp and actually warm the occupant in winter cold conditions. In fact on "High", it gets a little uncomfortably hot... you might not want to go with quite as large of a series resistor that I used, which was 2.2 kOhm.

The general theory of operation is there are thermistors with negative temperature coefficiets in the seat back and bottom that relay changing temp information to the seat heater control module. As the seat warms up, the thermistor value decreases and the sensing current increases. To make the seat get hotter, I cut into the circuit and added a fixed, non changing resistor inline with the thermistor. This shifts the entire temperature control behavior "up". The amount of the shift will depend on the resistor used.

I updated the photo link with some pics of the seat heater control module (its under the passenger seat), how I used an electrical heater blowing on the driver seat to isolate that seats thermistors (as the seat warmed up I can measure which resistance values were getting smaller), which leeds in the heater control module I cut, the 2.2k ohm resistors soldered in series across the cuts, and then pics of the new seat temps after returning from home this afternoon (the bottom cushion is a little hotter than shown when sitting on it, but the seat surface cools off rapidly with the door open and 20F outside temps and by the time I aimed the gun there it had decreased to that level).

Link to pics: https://photos.app.goo.gl/hPzrLsKoy9SG4Vom7

Immediate temp measurements show around 118-120F on the seat back on high, 104-106F on low, and similar on the seat bottom. You could decrease this by going to a lower value series resistor.
 
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#11 ·
Thanks.

You should be able to zoom in on the fairly high resolution pics int he google link. Hopefully that's enough. A quick verbal description is the thermistor leads for the driver seat are on the outside row, 3rd ones in from each side. I placed black marker "dots" on the driver thermistor leads in one of the pics that's easy to see when you zoom in. The zoom in should also show you the leads being cut and separated. The resistors just bridge across the cut leads (one terminal on each side of the cut lead).

The larger connector has fatter leeds and carry the switching FETs current that goes to the actual heating elements.

It was -10F this morning on the drive to work. I had to turn down the seat heat setting to 2 instead of 3 as my back side was getting too hot. And this is with a heavy winter parka. Before this mod I couldn't tell if the seat was even on when wearing winter clothing due to the pathetic heat output.
 
#7 ·
An asside on the term Nanny State

Sorry to be way off topic, but I'm curious why you used the term "Nanny State" in the original post when in fact it was private individuals suing a private company that caused the situation you are complaining about. And the damage payments were awarded by 12 person juries of non-governmental employees. I've lived in other countries where government magistrates have a lot more power to dismiss cases. In my experience there are many fewer damage awards made to stupid people when the "state" is more involved.

So ... looks to me like the blame lies with the people, rather than the state.
 
#8 ·
Sorry to be way off topic, but I'm curious why you used the term "Nanny State" in the original post when in fact it was private individuals suing a private company that caused the situation you are complaining about. And the damage payments were awarded by 12 person juries of non-governmental employees. I've lived in other countries where government magistrates have a lot more power to dismiss cases. In my experience there are many fewer damage awards made to stupid people when the "state" is more involved.

So ... looks to me like the blame lies with the people, rather than the state.
Fair comment. Perhaps the term “state” is being used in the context of “culture” or “society” rather than “government”.
 
#10 ·
I've never had an issue with my '17 Bolt's heated seats. Whenever I do turn on the seat heaters manually, I never set them higher than 1.
From the "seat of the pants" feel, my '12 Volt's heated seats do seem a bit stronger than my Bolt's, but the Bolt's seats still supply plenty of heat for me.
 
#15 ·
Take an infrared heat gun to the seat to get a dispassionate measurement of how hot its actually getting. You may be surprised on how "hot" the seat isn't.
I will try that this week, just to see what measurements I get.
However, I agree with Sean Nelson, 3 dots is to hot for comfort.
It takes longer, but I can feel definite heat, even through a 1/2” sheared sheepskin cover. I too turned off the AUTO HEAT selection, anyone in passenger seat turns it on manually, & so far everyone thinks 3 dots is too warm. The Bolt seems to be at the same level as my Benz, which is also to hot if turned fully up.
I’m not sure the infrared measurements are valid. The heating grid is below the top surface of the seat. When you sit on it, the top fabric & foam compresses, essentially making the substrate more dense, which transfers the heat better, & creates a better “heat sink”.
As soon as you get out of the seat, the material expands, & fabric, having little density or thermal mass, cannot retain much heat. Within seconds,(especially on a cold day with a large temperature delta), the seat cover will cool considerably.
Have you tried placing a thermometer on the seat, with a weighted blanket on top, (simulating your azz), to see what the temp reads?
Also remember that you don’t need 98.6F to feel warm, or to “add heat”. That value is basal temp, your core temp. Skin temp, especially top of arms & legs can be considerably lower.
I don’t think the Canadian models use a different controller or heat element, but the few times I’ve tried it on my 2018 LT, 3 dots is too much.
 
#16 ·
Thanks. I look forward to your measurements.


I wonder if some of the variability is between the leather seats in a Premiere and the cloth seats in the LT? Although we'd need some actual measurements from more owners to know this... Are those of you who have "hot" heated seats in an LT or Premiere?



Agree on the rapid cooling when getting out of the seat. I mentioned the initial seat surface temps being hotter than what the pics show from the infrared heat gun. And the temps do drop rapidly. The hottest measurements of ~120F came from doing a quick lean forward and shooting at the seat back within 1 second. But with the OEM seat heater control module setup the seats would only get to ~95F with this quick measurement, which is roughly what skin temp is for a normal ambient situation for most humans, so my seats weren't "adding" much of any heat: http://www.healthyheating.com/Definitions/facts_about_skin.htm


The emissivity of leather is basically the same as human skin, so the temps from the infrared heat gun should be accurate.

https://www.optotherm.com/emiss-table.htm


I'm not sure of the material in the LT seats and what is its emissivity, so a heat gun could give false readings on that fabric.
 
#19 ·
NOTE: Always disconnect the 12V battery for awhile before messing with seat connectors due to airbags in the seats...

One of my grips with the Bolt used to be due to the pathetic amount of "heat" the "heated seats" would create. The heated steering wheel is great and will get up to ~120F, which will add heat into the body. The OEM Bolt seats would not even get above body temp, so they don't really "add" warmth to the occupants. And the amount of heat was far less than any of my other vehicles with heated seats.
Sorry if this is a bit off topic, but since you have been working with the seat heaters you might be able to give me some advice.

The heated rear seat on the driver's side stopped working. If you push the button to activate nothing happens. The indicator light doesn't even come on.

My 2017 Bolt has 46,000 miles and is out of warranty for this. Could it be something as simple as a fuse? If so, do you know which one to check?
 
#20 ·
I haven't messed with the rear seats, so I have no specific info to share. Sorry. But based on your description, checking the fuse sounds like a good place to start.

There are good youtube videos that show and describe the diagnosing and fixing of heated seat issues. That should be helpful if something simple like the fuse doesn't fix things. There's several things that can go wrong, but if you're somewhat mechanically inclined, have the time and some simple tools it's generally a DIY to find and fix the problem.
 
#21 ·
https://my.chevrolet.com/content/da...als/2017/Chevrolet/BOLT EV/Owner's Manual.pdf

Page 265-266. The rear seat module is fuse 24, so that would be a good place to start. But if its blown, then I would expect neither side of the rear would work.

You could also check the rear seat heating module itself. I haven't investigated that one, so I'm not sure where its located or how to access it. The switching FETs inside are a common failure point and can often be visually seen to be bad due to melting...

Might also be the heating elements are damaged, which would measure as an high impedance or an open when probing the impedance with a multimeter. My front seat heating elements measured less than 2 ohms, which is typical for a good element.

Cold also be something with the thermistors in that seat...
 
#32 ·
Interesting. Thanks!

Did you happen to identify the leads to the passenger seat while you were at it? I guess I might be able to do that using the info you have already provided. :)
 
#33 ·
Glad to help and contribute to the knowledge base.


The passenger seat thermistors should be the two leads between the two I cut and modified for the driver seat. Those two had the same initial thermistor resistance readings as the two in the driver seat, and only reduced in value a little during the space heater testing (the entire cabin was getting a bit warmer as the space heater was running so the passenger seat temp increased a little, and its thermistor values decreased slightly).
 
#42 ·
Thanks.

Based on other GM heated seat module schematics (here's a Cruze one for example that is kinda close to the Bolt's, but not exactly the same: https://www.cruzetalk.com/forum/att...eat-question-seat-heat-electrical-diagram.jpg) I believe the thermistor path, and thus the resistors I added, have 5V applied to it. At worst case if the thermistor shorts out then the 2.2k resistors I'm using would have V^2/R = 5*5/2.2k=11mW. Or if its actually 12V instead of 5V, then worst case would be 12^2/2.2k=65mW. I believe the resistors I used are physically large and rated at 1/2W=500mW which has lots of margin on what it would ever see.

I didn't use high tolerance resistors. These were from my undergrad lab kit from many years ago :)

The seat heating elements were less than 2 ohms as I recall based on my multimeter measurement and their paths would have the 12V switched on/off via the switching FETs to modulate the power going to them to regulate the heat. V^2/R for the seat heating elements is pretty high power when the FET switches are "on", but the thermistor path is low power.

Here is an example "theory of operation" for the cruze seat heater:

Temperature Regulation
When the engine ON, the heated seats will initialize in the OFF state. With each activation of the heated seat switch, the seat heating control module will cycle the temperature setting in the following manner: HIGH, MEDIUM, LOW, and OFF.
The seat heating control module monitors the seat temperature through the temperature sensor signal circuit and the temperature sensor (thermistor) that is located in the seat cushion. The temperature sensor is a variable resistor, it's resistance changes as the temperature of the seat changes. When the temperature sensor resistance indicates to the seat heating control module that the seat has reached the desired temperature, the module opens the ground path of the seat heating elements through the heated seat element control circuit. The module will then cycle the element control circuit open and closed in order to maintain the desired temperature.
 
#44 ·
@TDIwyse, I have data for you

I used an Omega HH82 dual thermocouple digital thermometer, one thermocouple measured interior ambient, one measured the A** Interface Temperature, typically abbreviated as AIT.

The type of thermocouples used were fast read film type, (Type K), pictured, very low thermal mass for minimal error contribution.

Why not use a thermal camera? Because a thermal image has no relevance to the desired measurement, with a thermal camera you are measuring the surface temperature of a poor thermal conductor being convection cooled. By using the thermocouple and placing it in the back jeans pocket, at the optimal A** to Seat contact position, we can measure the interface temperature or AIT, directly perceived by the driver occupant.

Test conditions and measurements:
The Bolt drivers side seat heater was turned on to high and the temperature was allowed to stabilize for the duration of 2.5 radio airplay rock songs, or about 10 minutes.

Outdoor ambient as reported on Bolt display 40F
AIT = 107.5
Internal cabin ambient 70.5
Subject was a 165Lb male wearing levi 505 jeans.

And yes, I can only run my stock Bolt LT seat heater on high for a very short duration before I need to reduce the power level to avoid the dreaded "seat heater swamp A**" condition that would result. ;)
 

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#45 ·
@TDIwyse , I have data for you

I used an Omega HH82 dual thermocouple digital thermometer, one thermocouple measured interior ambient, one measured the A** Interface Temperature, typically abbreviated as AIT.

The type of thermocouples used were fast read film type, (Type K), pictured, very low thermal mass for minimal error contribution.

Why not use a thermal camera? Because a thermal image has no relevance to the desired measurement, with a thermal camera you are measuring the surface temperature of a poor thermal conductor being convection cooled. By using the thermocouple and placing it in the back jeans pocket, at the optimal A** to Seat contact position, we can measure the interface temperature or AIT, directly perceived by the driver occupant.

Test conditions and measurements:
The Bolt drivers side seat heater was turned on to high and the temperature was allowed to stabilize for the duration of 2.5 radio airplay rock songs, or about 10 minutes.

Outdoor ambient as reported on Bolt display 40F
AIT = 107.5
Internal cabin ambient 70.5
Subject was a 165Lb male wearing levi 505 jeans.

And yes, I can only run my stock Bolt LT seat heater on high for a very short duration before I need to reduce the power level to avoid the dreaded "seat heater swamp A**" condition that would result. ;)

Thanks for taking the time to do this and reporting.



I don't agree with your assessment about the lack of accuracy with the thermal gun/camera for the condition of extended "on time" of the seat heater and a human sitting in the seat. The temperatures will stabilize even though the seat material is a poor conductor. 25 minutes of riding in the seat with the seat heater on is more than enough time to fully "saturate" the thin leather material and have a stabilized temperature. However, you do need to have an emissivity close to 1 for the thermal gun/camera to give an accurate result. Your LT seat material is likely too far below 1 to give an accurate result based on the emissivity chart link I posted earlier. But leather, as with the seat of the Premiere, is very close to 1, and will thus give an accurate reading.


But I will test this additional measurement approach with a similar method you used to compare to the results I got with the thermal gun and report back.
 
#54 ·
I’m jumping in late here, but just to add a data point:
17 Primier.
Automatic mode during pre conditions just about removes the ice cube feeling.
Automatic mode during use - useless
3 light manual mode - take about 20 min to really feel warm if the weather is cold enough to want heated seats in the first place.

I previously had a 12 Cruze LTZ and the heated seats in it would indeed become uncomfortably hot after 5 minutes on high in anything but the coldest VA weather (say aroun 0deg F). I miss those seats!

I hadn’t looked at this post before because I can’t really picture myself doing the mod, but now I’m thinking I just might!
 
#56 ·
...
3 light manual mode - take about 20 min to really feel warm if the weather is cold enough to want heated seats in the first place.
...
This would be the mode I'm most interested in. Would you be able to take some temperature measurements and reply back? I think we're to the point where we don't need pics, although please add those if you can. However it would be good if at least some discussion of how the measurement was taken, what was the measurement device, and waiting long enough so the seat has time to stabilize at its max temperature.
 
#59 ·
I don't have any hard data like temperature measurements to share, but in manual "3-dot" mode the seats in my 2017 Premiere become too hot for me within 5 to 10 minutes and I have to turn them down to the "2-dot" level. I agree that automatic mode is completely inadequate.
 
#60 ·
2017 Premier on 3 dots. Measured after ~15 mins. Ambient temp was about 28°F.
Seat back = 108°F (42°C)
Seat bottom = 100°F (38°C)

It occurs to me that I took the measurements with a thermal camera, so that's the hottest spot. The average temp would be lower.

Subjectively, I've been ok with "Auto" mode - particularly if I've remembered to precondition. It's like sitting in a seat someone else recently got up from.
The 3 dot setting was noticeably warm, but I wouldn't say hot. After 15 mins there was no need to turn it down.
 
#62 ·
2017 Premier on 3 dots. Measured after ~15 mins. Ambient temp was about 28°F.
Seat back = 108°F (42°C)
Seat bottom = 100°F (38°C)
...
Thank you.

This is beginning to get interesting. Already there is a wide distribution in the reported temps. The design might just be such that there is large standard distribution in the temperature control range and some of us get the lower end of the distribution.
 
#65 ·
Ok, I drove home from work, about 20mi and stoped at Harbor Freight, about half way, and picked up an infrared thermometer. Temp in car set to 73. Left the car running at home with seat set to 3. After 20min the temperature read from 73 to 83 deg. To me this means "barely functioning". At this point I'm wondering if this is worth a warranty visit to the dealer. BTW, I pointed new thermometer at one in the house and they read the same within 1deg, so I don't the thermo' is miss calibrated. Outside air temp about 45.
 
#66 ·
73 to 83 is way too low. How does the seat feel when you're sitting in it and the heated seats are at 3? If it's not at least = body temp, then I'd go to the dealer.
What might be happening is that the surface of the seat is loosing heat to the interior of the cabin, so it reads more or less the same as cabin temp. If you sat on it (ie, insulated it), it might get warmer. Just a thought.
 
#68 ·
Here are my results in our 2018 LT using a temperature probe from a digital kitchen thermometer. I will try to verify the accuracy of the probe by comparing it to an IR thermometer later this week. I was sitting on the temperature probe with it under my right thigh.
- Starting temperature - 23°C (73°F).
- after 5 minutes - 35°C (95°F).
- after 10 minutes - 37°C (98°F).
- after 15 minutes - 38°C (100°F).
- after 20 minutes - 39°C (102°F).
- after 25 minutes - 40°C (104°F).

I then moved to temperature probe the seat back, a little above the small of my back. So at this point the seat had been on for twenty-five minutes. After five minutes of stabilizing the seat back temperature seemed to be 40°C (104°F). The same as the seat bottom.

My question after this is: what size resistors should I use if I want to increase the max temperature from 104°F to closer to 120°F?
 
#70 ·
Thanks for doing this.

If you want to be precise, measure the thermistor value from the seat heater module after the interior temp has stabilized for 2 different temps (the farther apart the better). That would give you the slope for the negative temperature coefficient of your individual thermistors. You can then plot the line and project to the 104F point where your seats stabilize, and to the desired final temp of 120F. The delta R between 104 and 120 would be the amount of additional resistance you'd want to add.

Here's a good quick read on NTC thermistors and shows some example curves for a ~10K NTC thermistor and would show the kind of graph I'm talking about above.

https://components101.com/ntc-thermistor-10k

If you want a quick "projection" from my results, which may not work precisely for you as we may have variations in our thermistor behaviors... your seats are getting about 9-10F hotter than mine were. The 2.2k took mine from ~95 to ~120 on High, or a 25 deg delta. If you want to go from ~104 to ~120, or a 16 deg delta, I'd estimate 16/25*2.2k-> 1.4k would get you close. Larger values will shift it hotter.
 
#69 ·
I have a 19 LT. I would describe it as:
3 dots - eventually too warm (~20 mins)
2 dots - can be left on indefinitely, most of the time
1 dot - the only indication it's working is the dot on the screen

I would agree the seat heaters are the weakest I've experienced, but I can understand Chevy backing them off.
The above is with wearing jeans in temperatures 0F and colder.
If people are expecting to start shivering and be wearing insulated coveralls that are chilled from being outside, then get into the car and get warmed up just from the seat heaters in a couple of minutes, that isn't going to be successful.

I would like to see an "arctic heater" option that has more oomph, but I don't think most people need it and I'm in MN and we had -30F. Eventually the seat heater got hot enough that I needed to turn it down. Soldering in resistors is a good workaround, but not a change I'm fond of.

Also, if you go beyond 3 settings, you will then need different UI, cycling through one button would have to be replaced with up/down or something, eating valuable screen real estate.
 
#71 ·
...
Also, if you go beyond 3 settings, you will then need different UI, cycling through one button would have to be replaced with up/down or something, eating valuable screen real estate.
We could wire in external potentiometers instead of the internal R's and then have lots of control range, and independent control of the seat bottom and back :)
 
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