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Hey guys, I've seen a few threads around the forums discussing adding OEM heated seats, but haven't seen anyone complete it. These cars are getting more common in junkyards now which should help bring the cost of this swap down considerably. I was at the junkyard the other day and found a 2LT with a pretty nice interior, so I'm going to document my attempt at this and we'll see how far I can get.

My car is a 2011 Eco, with the base manual cloth interior. I did a full interior swap since the dirty gray was ugly, but the only parts I think you need will be the seats and the control module. If at all possible, try and get the vehicle side harness that connects the seats to the harness under the carpet - 6" or so would be good. It will make the wiring much easier later on. You will also want to make sure the seat comes with the heater control unit installed underneath - if you pull it yourself it will, but if you buy it off the shelf it's possible it could have been removed before sale.

Wiring is of course the main trick. Here's what I've figured out so far:

  • my Eco was already pre-wired for power seats, with the fuse already in place under the dash. I don't know if this will also be true for LS cars, but I'm guessing 1LT cars will be the same. That's awesome, because I was able to just drop the seats in for now and continue driving while I plan out the heated seat portion later.
  • The control switches should be plug and play. The base HVAC switches and the ones with the heated seat button integrated both use a single 3-pin connector to communicate with the main HVAC module.
  • There are 8 wires missing from the driver side harness that you'll need to run yourself. 5 wires run between the driver and passenger side seats to communicate for passenger heating (could possibly skip these for ease of install, but I'll come back to this.) The other 3 are B+, ground, and low speed GMLAN communication. If you got the vehicle side harness as suggested earlier, you can pop the white plastic retainer off the ends and make yourself a pigtail harness by moving each missing wire to your own harness.
  • The GMLAN wire is missing from the driver side harness - however, it IS present on the passenger seat harness, due to the occupant sensor. I think I can tap into this wire to allow the seat heater module under the driver seat to communicate with the BCM and heater controls. Since I have to run one wire from the driver to passenger seat, I might as well run the other 5 and have both seats functional.
  • The heated seat fuse is also preinstalled on my Eco, and connecting a multimeter showed that it has +12V running through it. I'm still trying to figure out where it goes from there so that I can run the second 12V line to the driver seat. In theory I think you could reuse the power seat line, but that's a little sketchy and also would allow you to run the heated seats indefinitely with the ignition off - probably not a great idea.
  • Cost: at a local pick-a-part, I pulled the entire interior - front/rear seats, door panels, bolsters, dash trim, and the HVAC controls - for $305 including tax. For just the seats and controls, it would have been around $100. My assumption is that programming will be another $200 or so, so I think this can be done for around $300 total.

Things I still don't know:

  • Programming - I'm pretty sure BCM programming will be needed to enable heated seats. Maybe I'll be pleasantly surprised on this, but I'm not counting on it. I know White Auto Media specializes in this kind of custom programming so that's an option. Possibly a helpful dealer with an MDI would be willing to reflash it also.
  • Does the HVAC control module itself require any programming? I'm not sure on this yet. If so, could the module be replaced with one from a heated seat car?

Summer is just kicking in so updates will be a bit slow in this thread until I can work through a few other projects I have. Still, I plan to daily this car through the fall/winter so I will definitely be coming back to this as time/ideas warrant. If anybody else has given this a try, let me know what you've found out!
 

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Hey guys, I've seen a few threads around the forums discussing adding OEM heated seats, but haven't seen anyone complete it. These cars are getting more common in junkyards now which should help bring the cost of this swap down considerably. I was at the junkyard the other day and found a 2LT with a pretty nice interior, so I'm going to document my attempt at this and we'll see how far I can get.

My car is a 2011 Eco, with the base manual cloth interior. I did a full interior swap since the dirty gray was ugly, but the only parts I think you need will be the seats and the control module. If at all possible, try and get the vehicle side harness that connects the seats to the harness under the carpet - 6" or so would be good. It will make the wiring much easier later on. You will also want to make sure the seat comes with the heater control unit installed underneath - if you pull it yourself it will, but if you buy it off the shelf it's possible it could have been removed before sale.

Wiring is of course the main trick. Here's what I've figured out so far:

  • my Eco was already pre-wired for power seats, with the fuse already in place under the dash. I don't know if this will also be true for LS cars, but I'm guessing 1LT cars will be the same. That's awesome, because I was able to just drop the seats in for now and continue driving while I plan out the heated seat portion later.
  • The control switches should be plug and play. The base HVAC switches and the ones with the heated seat button integrated both use a single 3-pin connector to communicate with the main HVAC module.
  • There are 8 wires missing from the driver side harness that you'll need to run yourself. 5 wires run between the driver and passenger side seats to communicate for passenger heating (could possibly skip these for ease of install, but I'll come back to this.) The other 3 are B+, ground, and low speed GMLAN communication. If you got the vehicle side harness as suggested earlier, you can pop the white plastic retainer off the ends and make yourself a pigtail harness by moving each missing wire to your own harness.
  • The GMLAN wire is missing from the driver side harness - however, it IS present on the passenger seat harness, due to the occupant sensor. I think I can tap into this wire to allow the seat heater module under the driver seat to communicate with the BCM and heater controls. Since I have to run one wire from the driver to passenger seat, I might as well run the other 5 and have both seats functional.
  • The heated seat fuse is also preinstalled on my Eco, and connecting a multimeter showed that it has +12V running through it. I'm still trying to figure out where it goes from there so that I can run the second 12V line to the driver seat. In theory I think you could reuse the power seat line, but that's a little sketchy and also would allow you to run the heated seats indefinitely with the ignition off - probably not a great idea.
  • Cost: at a local pick-a-part, I pulled the entire interior - front/rear seats, door panels, bolsters, dash trim, and the HVAC controls - for $305 including tax. For just the seats and controls, it would have been around $100. My assumption is that programming will be another $200 or so, so I think this can be done for around $300 total.

Things I still don't know:

  • Programming - I'm pretty sure BCM programming will be needed to enable heated seats. Maybe I'll be pleasantly surprised on this, but I'm not counting on it. I know White Auto Media specializes in this kind of custom programming so that's an option. Possibly a helpful dealer with an MDI would be willing to reflash it also.
  • Does the HVAC control module itself require any programming? I'm not sure on this yet. If so, could the module be replaced with one from a heated seat car?

Summer is just kicking in so updates will be a bit slow in this thread until I can work through a few other projects I have. Still, I plan to daily this car through the fall/winter so I will definitely be coming back to this as time/ideas warrant. If anybody else has given this a try, let me know what you've found out!
Following.

Let me know if you figure this out. I started down that rabbit hole a few years ago and stopped at the controls as it seemed as if it were a bit insurmountable, but maybe I missed something.

This was the beginning for me.

How I swapped in power seats
How I Swapped in Power Seats part 2
How I removed and replaced my Rear Seats
How I removed and replaced my Rear Seats pt 2
 

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In case you don't know, the heated seats use serial communicatiom with the HVAC control head. I do not know about module swap compatibility without programming like you said. But I can assure you that the seats aren't a simple "enable/disable" like heated steering wheels are.

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2014 LT program car, Pull Me Over Red, 1.4T Auto
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In case you don't know, the heated seats use serial communicatiom with the HVAC control head. I do not know about module swap compatibility without programming like you said. But I can assure you that the seats aren't a simple "enable/disable" like heated steering wheels are.

Sent from my SM-G781V using Tapatalk
Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, ...
 

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A PWM signal is an analog voltage. The HVAC control module uses serial communication with the heated seat module. If it was a PWM signal talking to the heated seat module, it'd be easy to fake it out without the HVAC module. Since it is not, I'm not sure if you could can do it without the correct HVAC control module, which probably needs to be VIN matched to the car. Clips from the service manual for 2011 Cruz below.


Art Font Pattern Circle Number


Rectangle Font Slope Parallel Pattern
 

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A PWM signal is an analog voltage. The HVAC control module uses serial communication with the heated seat module. If it was a PWM signal talking to the heated seat module, it'd be easy to fake it out without the HVAC module. Since it is not, I'm not sure if you could can do it without the correct HVAC control module, which probably needs to be VIN matched to the car. Clips from the service manual for 2011 Cruz below.


View attachment 297668

View attachment 297667
Art Font Circle Technology Pattern


If that is the case, where is this voltage applied and what is that voltage/waveform etc.?
Also where is that diagram from?
 

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Diagram and verbiage are straight from the service manual. Serial com is digital, so a bunch of 1s and 0s. It is not PWM.

Sent from my SM-G781V using Tapatalk
 

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Diagram and verbiage are straight from the service manual. Serial com is digital, so a bunch of 1s and 0s. It is not PWM.

Sent from my SM-G781V using Tapatalk
Do you know where the voltage is applied in that circuit per the highlighted statement?
 

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Full disclosure I am not familiar with any of the hardware.

Simply going by the circuit diagram (if it's right, I've found the service manuals to have circuit errors in the past), terminal B on the x1 connector. Probably a two pin connector. That is the B+ that turns the heated seat module on, and supplies the high current (30A according to the diagram). It would be ignition switched (so the module doesn't stay on all the time). The com wire is on x3 terminal 11. If you've got the harness, it says it's blue. The connectors are numbered too, so it's easy to find.

That's about the best I can do.

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Full disclosure I am not familiar with any of the hardware.

Simply going by the circuit diagram (if it's right, I've found the service manuals to have circuit errors in the past), terminal B on the x1 connector. Probably a two pin connector. That is the B+ that turns the heated seat module on, and supplies the high current (30A according to the diagram). It would be ignition switched (so the module doesn't stay on all the time). The com wire is on x3 terminal 11. If you've got the harness, it says it's blue. The connectors are numbered too, so it's easy to find.

That's about the best I can do.

Sent from my SM-G781V using Tapatalk
So the actual voltage applied is just line (battery) voltage?
 

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What's labeled "B+" on the left side of the diagram yes. When you turn the key to "ON," the BCM turns on a relay that energizes that circuit, turning on the heated seat module. The HSM then waits for some kind of message on the other wire from the HVAC module to tell it to heat the seat.

The relay exists for two reasons. First, to turn on the HSM ONLY during key on. The second, so that the BCM can load shed if the battery voltage is too low.

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That tells me I should be able to use a Raspberry Pi and some simple programming to run my factory heated seats sans the factory controller. (I have long ago dumped the other parts.)
 

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If you can figure out what the heated seat module wants to see in order to turn on the heat (level one two three), that certainly would work. Would be pretty awesome.

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Discussion Starter · #14 · (Edited)
Hey guys, glad to see this picked up some momentum. I've been looking through the schematics in AllData and I think I can answer some of these questions:

Power - B+ comes from the underhood fuse block (fuse 33) and is a 2.5mm red/white wire. This wire will need to be run through the firewall since it doesn't exist on our harness. Oddly, according to the description, this wire is always powered - if you were willing to be a bit hacky you could probably just reuse the red/brown power seat wire as an input, although it is a bit smaller (1.5mm). Ground is a black 2.5mm wire. The driver seat harness also provides 12V power to the passenger heated seat (Brown/Dk Blue positive, Black/Dk blue return.)

The HVAC module sends a command to the heated seats over low speed GMLAN (dark green wire). Our module is most likely not sending this command and will need to be reprogrammed or replaced with the module from a 2LT car with heated seats/manual HVAC. That's one piece I forgot to grab out of the junkyard. I doubt this is VIN locked, given the age of the car and the fact that it's not a critical safety component like the ECU or BCM; I'm guessing this can just be swapped in. It's located behind the glovebox, next to the blower fan. Here's the operation description:

The driver and passenger heated seats are controlled by a single seat heating control module that is located under the driver seat cushion. Both heated seats are controlled by separate heated seat switches that are located in the HVAC control. When a heated seat switch is pressed, a serial data message is sent from the HVAC control to the HVAC control module indicating the heated seat command. The HVAC control module then serves as a gateway to transmit the message to the seat heating control module via the serial data line. In response to this signal, the seat heating control module applies battery positive voltage through the element supply voltage circuit to the appropriate seat heating elements. The seat heating control module then sends a serial data message back to the HVAC control module to gateway the information to the HVAC control to either illuminate or turn off the appropriate temperature indicator.
From that it sounds like the brains involved are just the seat heater module, the control panel, and the HVAC module. Could be plug and play!

EDIT: Side note, since I'm looking at the HVAC module schematic... the only communications lines the module has are the dark green GMLAN (seats), green/yellow (control panel), and dark blue/gray blower speed control, which goes directly to the blower motor controller. It's possible that replacing the HVAC module and blower motor module as a pair would allow you to use the 6 position fan switch from the later 2013-2015 Cruze. Hmmmm.
 

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Just curious as to why they have a fuse in the heated seat module spot if it wasnt wired for heated seats, which mine doesnt have heated seat. Im planning on getting a set of leather power seats that are heated. Getting the heat part working would be a bonus but nothing big. 🖖
 
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