Laramie heated seats wiring question

[Steevo]

My 2020 3500 CCSB has the heated/ventilated seat in front. I would like to install a small switch in the side panel of the drivers seat to allow me to turn the seat bottom heat off/on so that I could run lumbar heat without butt heat. Does anyone here know what wires in the under-seat space go to the seat heating pad?

Thanks

 

[Jimmy07]

On the bottom of the driver seat is the heated seat module. Look for the white connector with 5 wires. The orange/pink wire is the supply for the driver seat cushion, so that’s the one you want to switch off.
A couple issues though:
If the heated seat module detects an open circuit on either of the heat pad suppliers, it will store a fault and automatically shut the circuits off for the whole seat.
You’d have to use a resistor on a relay, so when you switch that circuit off, the heated seat module is still presented with the expected heat pad resistance.
Then, since there are three different settings, it’s looking for a different resistance for each setting, and will fault if the values don’t match. So basically, you have to choose which setting you want the seat back to be on when you switch the seat cushion off, and use a resistor of the same value of that particular setting.

 

[jsalbre]

On the bottom of the driver seat is the heated seat module. Look for the white connector with 5 wires. The orange/pink wire is the supply for the driver seat cushion, so that’s the one you want to switch off.
A couple issues though:
If the heated seat module detects an open circuit on either of the heat pad suppliers, it will store a fault and automatically shut the circuits off for the whole seat.
You’d have to use a resistor on a relay, so when you switch that circuit off, the heated seat module is still presented with the expected heat pad resistance.
Then, since there are three different settings, it’s looking for a different resistance for each setting, and will fault if the values don’t match. So basically, you have to choose which setting you want the seat back to be on when you switch the seat cushion off, and use a resistor of the same value of that particular setting.

Wouldn’t the resistance be relatively static and just the voltage being reduced (or switched with PWM) for settings less than high? You should be able to put a multimeter on the pad leads and determine the proper resistance.

 

[Jimmy07]

Wouldn’t the resistance be relatively static and just the voltage being reduced (or switched with PWM) for settings less than high? You should be able to put a multimeter on the pad leads and determine the proper resistance.

That’s actually most likely the case. Although, when reading the system status of the heated seat module with AlfaOBD, I notice the voltage doesn’t change between settings and status reads. But, that could just be an issue with AlfaOBD because it doesn’t technically support the 2019+ heated seat modules, only up to 2018.

 

[jsalbre]

That’s actually most likely the case. Although, when reading the system status of the heated seat module with AlfaOBD, I notice the voltage doesn’t change between settings and status reads. But, that could just be an issue with AlfaOBD because it doesn’t technically support the 2019+ heated seat modules, only up to 2018.

It may not show any difference if it’s PWM, since the voltage output would remain the same. I’m kinda curious now though. I may hook up some probes on my heated seat module and do some testing. Unfortunately I don’t have a scope anymore so I can’t really look for PWM.

 

[Steevo]

Thanks for the great information, I appreciate it.
This is sounding more complicated than I hoped it might be.

 

[jsalbre]

Thanks for the great information, I appreciate it.
This is sounding more complicated than I hoped it might be.

Don’t give up hope yet, it may not be complicated at all. We just don’t quite know.

 

[Jimmy07]

Ok, working backwards off the seat cushion heating element open circuit fault, looks like a 2.5 ohm resistor will do:


But, a different issue will pop up that will shut off the driver heated seat all together- the seat cushion won’t reach it’s target temperature:

 

[Steevo]

So, a DP switch that re-routed the current back through a resistor would simulate a load for the PCM module, but then the module thinks it is heating the cushion but senses no heat, sending the PCM brain into an endless feedback loop until it decides the cushion is bad and shuts it down altogether. Gotta love computer controlled everything . . .

But thank you Jimmy07 for the great in-depth analysis.