LX570 Passenger Seat Heater ECU - Possible Solution

[lx200inAR]

My driver-side seat won't heat or vent. The control knob lights up but nothing happens. Following what others did, I got an LS driver-side ECU from eBay and did the swap, but the seat climate functions still don't work.

Next, I checked all the fuse boxes in the engine bay, driver's side, and the passenger side... all were good.

What else am I missing here?

View attachment 3244106

Did you get a front seat or a rear seat?

 

[mzhu]

Did you get a front seat or a rear seat?

It was a front-seat ECU. Going to swap the passenger-side ECU which is working to the driver's side next.

 

[lx200inAR]

Do you have Techstream? It connects to the seat ECUs. It would interesting to see what it thinks about the ls ecu.

 

[mzhu]

Do you have Techstream? It connects to the seat ECUs. It would interesting to see what it thinks about the ls ecu.

I don't have a Techstream. From what I can see after opening up both ECUs, I could not tell a difference between the circuit boards.

 

[Zjohnsonua]

My driver-side seat won't heat or vent. The control knob lights up but nothing happens. Following what others did, I got an LS driver-side ECU from eBay and did the swap, but the seat climate functions still don't work.

Next, I checked all the fuse boxes in the engine bay, driver's side, and the passenger side... all were good.

What else am I missing here?

View attachment 3244106

Following this one. Passenger side in ours has the same problem of no function but the switch light illuminates.

 

[mzhu]

I just swapped the ECUs between the driver's side and the passenger side (which is working). The passenger side works with the new LS ECU, driver's side still doesn't work.

This means it's not the ECU but something else.

 

[RunTheDistance]

Just wanted to do a follow up on this. My passenger seat was not heating or cooling and no light coming on. I bought and swapped the LS part from a similar year. Everything is working again! Pretty happy on the savings of the LS part vs the LX.

 

[mzhu]

Problem solved!

After consulting with another LX owner on an LX570 Facebook group, he figured it out. We both had exact same troubleshooting steps: checking all the fuses, under-seat connectors, switching out ECU and the only thing that was missing was a plug that was located behind the seat-back area. See pics below:

This is what it looks like after you remove the back cover of the seat. It's a relatively straight forward process. Loosen two bungee straps on the bottom, remove two screws in the mid-section, then pull the backing downward to remove.

After taking off the back cover, there's one white plug that's right next to the vent. Upon a closer look, the wires attached to the bottom portion of that plug had somehow broken clean off.

To fix this issue, I had to break off the last hanging wire, re-pin the entire plug with new wiring and then solder the new wires onto the existing wiring harness.

To remember which colored cable goes where, I marked the original locations with G (grey), Gr (green), B (blue), and R (red).

I added some solder to the pins to ensure the connections are secure.

Now solder them to the existing wiring harness.

Once that was done, I plugged it back in, and Voilà! The heat/vent both work now. I hope this helps those who are still struggling with their broken seat climate issues.

 

[lx200inAR]

Problem solved!

After consulting with another LX owner on an LX570 Facebook group, he figured it out. We both had exact same troubleshooting steps: checking all the fuses, under-seat connectors, switching out ECU and the only thing that was missing was a plug that was located behind the seat-back area. See pics below:

This is what it looks like after you remove the back cover of the seat. It's a relatively straight forward process. Loosen two bungee straps on the bottom, remove two screws in the mid-section, then pull the backing downward to remove.
View attachment 3260515

After taking off the back cover, there's one white plug that's right next to the vent. Upon a closer look, the wires attached to the bottom portion of that plug had somehow broken clean off.
View attachment 3260518

To fix this issue, I had to break off the last hanging wire, re-pin the entire plug with new wiring and then solder the new wires onto the existing wiring harness.

View attachment 3260522
To remember which colored cable goes where, I marked the original locations with G (grey), Gr (green), B (blue), and R (red).

View attachment 3260524
I added some solder to the pins to ensure the connections are secure.

Now solder them to the existing wiring harness.
View attachment 3260529

Once that was done, I plugged it back in, and Voilà! The heat/vent both work now. I hope this helps those who are still struggling with their broken seat climate issues.

Good find. I suspect this means that you wouldn't have seen an error in Techstream. This was sort of the issue I had when I got my LX570 originally. Only mine was just unplugged. There are 2-3 plugs that go between the bottom and seat back. I think the dealership had probably had the seat apart to try and freshen up the leather and when they put the seat back together they didn't reconnect any of the connectors. I was able to see this in Techstream as a failed sensor.

The difference in our failure modes is that the light did not work on mine, because the ECU essentially just shut everything down due to the failed (unplugged) sensor. I suspect your broken cables were probably what actually power the cooling/heating, so the ECU didn't know anything was wrong.

 

[Grumvee]

Massive thank you and props to @turbotwo!

I ordered that part number (#85861-50052 ) off of eBay for $100, and fixed this issue that has vexed me since I bought the vehicle 2 years ago.

My wife also thanks you. We spent winter weekends skiing in the Sierras, and her butt will now be warm

 

[turbotwo]

Massive thank you and props to @turbotwo!

I ordered that part number (#85861-50052 ) off of eBay for $100, and fixed this issue that has vexed me since I bought the vehicle 2 years ago.

My wife also thanks you. We spent winter weekends skiing in the Sierras, and her butt will now be warm

Nice, I'm glad you got it sorted out! I live in the Canadian prairies so I understand the importance of having a seat heater for the wife!

Does yours get heat on both the lower back and the seat cushion? My passenger side only seems to heat the lower back, so I'm not certain whether to blame the ECU or if there's actually a problem with the heater in the seat. Either way it works well enough that I'm not highly motivated to address it.

 

[Grumvee]

Yes ours works for the seat and the lower back

 

[RocketCityCrzrs]

Reviving this a little bit in case anyone is still following. With you guys that had ECU failures, was your light coming on? My driver's seat will not heat or cool, but the light comes on. Also text stream shows voltage changes on the heat and cool circuit when you operate the switch, which makes me think that the ECU is probably okay and reporting back correctly. My passenger seat heats but doesn't cool, and text stream, again, shows normal functionality and voltage changes when you maneuver the switch.

 

[Zjohnsonua]

Reviving this a little bit in case anyone is still following. With you guys that had ECU failures, was your light coming on? My driver's seat will not heat or cool, but the light comes on. Also text stream shows voltage changes on the heat and cool circuit when you operate the switch, which makes me think that the ECU is probably okay and reporting back correctly. My passenger seat heats but doesn't cool, and text stream, again, shows normal functionality and voltage changes when you maneuver the switch.

My PS seat neither heated nor cooled. Light stayed on. Replaced board with the LS unit. Seats now work.

 

[tbisaacs]

I replaced my 08 LX570 DS seat ECU with a used LS460 ECU. It required swapping cases but that took 5 minutes.

This fixed multiple symptoms:

• Seats would heat for a few minutes and then stop but light remained on
• Seat heat would not turn off and light would blink when dial was in middle position.

1-banana job and great opportunity to clean under seats and replace the seat fan filter

 

[lx200inAR]

View attachment 3818627

I replaced my 08 LX570 DS seat ECU with a used LS460 ECU. It required swapping cases but that took 5 minutes.

This fixed multiple symptoms:

• Seats would heat for a few minutes and then stop but light remained on
• Seat heat would not turn off and light would blink when dial was in middle position.

1-banana job and great opportunity to clean under seats and replace the seat fan filter

I also did this last week with my passenger seat. Mine was completely inoperable. Works fine now.

 

[loualbano]

Has anyone tried 85861-50191?

85861-50191 Genuine Lexus Part

Genuine 85861-50191 Computer, Seat Climate Control, Front RH fits 2007-2009 Lexus LS460, LS600hL. LexusPartsNow offers 8586150191 for $947.04.

www.lexuspartsnow.com

According to that site, it's the previous part number for 85861-50052. There's a ton of the 85861-50191 on ebay.

 

[Omsok]

Doe anyone know if the front seat temperature control ECUs are specific for passenger or driver side?

Is a front ECU interchangable to left or right?

 

[Omsok]

Has anyone tried 85861-50191?

85861-50191 Genuine Lexus Part

Genuine 85861-50191 Computer, Seat Climate Control, Front RH fits 2007-2009 Lexus LS460, LS600hL. LexusPartsNow offers 8586150191 for $947.04.

www.lexuspartsnow.com

According to that site, it's the previous part number for 85861-50052. There's a ton of the 85861-50191 on ebay.

Did you try this one?

 

[Omsok]

I just swapped the ECUs between the driver's side and the passenger side (which is working). The passenger side works with the new LS ECU, driver's side still doesn't work.

This means it's not the ECU but something else.

Just to verify.
As far as you can tell the front ECUs are interchangeable between passenger side and drivers side?
Is this correct?