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markwilko79 · Jun 5th, 2020, 07:28

Hi,

This is a strange issue that I hope someone can help with. I have a 2016 XC70 and it has developed a problem where the power seat motors only move in one direction. Normally I would suggest that there might have been something jamming the motors but the odd thing with this is that all of the controls have the same issue slide, tilt, height etc. all move in one direction but not the other. What I have noticed is when you move any of the switches in the direction that the motors so not move you sometimes get a small blip of movement and then nothing and other times it does nothing. I can hear the relays clicking but no movement.

I have done some diagnostics and found the following:
Checked diagnostic codes with VDASH and there were a few codes, one said that a motor was short to ground (I believe). And the other said lost comms with the PSM. Cleared the codes and re-checked several times and no new codes generated.
Removed the memory module and manually connected power to the motors. They all moved in both directions fine which proves that the motors are basically OK. Plus I think if it was a motor at fault then the other chair movements would work OK. I think its unlikely that all the motors have failed at the same time.
This pointed to an issue with the PSM so I got hold of a replacement and it exhibited exactly the same issues albeit VDASH registered an error code saying the PSM software version was incorrect.
So the results of this suggest that the motors should be OK and it is more likely a control issue. Swapping out the PSM has (I believe) proven that the PSM is OK. So I'm at somewhat of a loss as to what might be the issue. A couple of other odd things (I believe) that might be indicators or could be contributing to the issue are that:
The power seat only works (in the directions that do work) when the engine is running and the doors are closed. This may be correct operation but I would have thought that it would work any time the ignition is on and would not be dependent on the doors.
The power window controls in the drivers door also inly work when the engine is running and all doors are closed. This could be unrelated but I don't think it used to do that and I think it only started at the point that the power seat failed.
So my thoughts on this are that
There may be a relay somewhere outside of the PSM that is triggered by the ignition that could be causing an issue. I don't have any of the wiring diagrams so can't tell. This might explain a link to the window controls if they run through the same relay
A ground or continuity issue, this again might explain not functioning when any of the doors are open but it feels like it's a control law issue as it doesn't seem to be based on door position but more based on the closed sensors.
A CEM/UEM fault. I'm not sure how the control laws work on the XC70 but the PSM doesn't work at all if the CAN connector is unplugged which suggests another controller on the CAN bus can enable/disable operation and maybe said faulty controller is giving false information to the PSM to stop moving the seat???
I've read a lot of posts on power seat issues but haven't seen anything the same as this. Hopefully someone has some ideas or has seen this before and can help. Thanks in advance.

Jun 5th, 2020, 07:28	#1
markwilko79 New Member Last Online: May 17th, 2022 23:57 Join Date: Jun 2020 Location: Herne Bay	Power Seat only moves in One Direction Hi, This is a strange issue that I hope someone can help with. I have a 2016 XC70 and it has developed a problem where the power seat motors only move in one direction. Normally I would suggest that there might have been something jamming the motors but the odd thing with this is that all of the controls have the same issue slide, tilt, height etc. all move in one direction but not the other. What I have noticed is when you move any of the switches in the direction that the motors so not move you sometimes get a small blip of movement and then nothing and other times it does nothing. I can hear the relays clicking but no movement. I have done some diagnostics and found the following: Checked diagnostic codes with VDASH and there were a few codes, one said that a motor was short to ground (I believe). And the other said lost comms with the PSM. Cleared the codes and re-checked several times and no new codes generated. Removed the memory module and manually connected power to the motors. They all moved in both directions fine which proves that the motors are basically OK. Plus I think if it was a motor at fault then the other chair movements would work OK. I think its unlikely that all the motors have failed at the same time. This pointed to an issue with the PSM so I got hold of a replacement and it exhibited exactly the same issues albeit VDASH registered an error code saying the PSM software version was incorrect. So the results of this suggest that the motors should be OK and it is more likely a control issue. Swapping out the PSM has (I believe) proven that the PSM is OK. So I'm at somewhat of a loss as to what might be the issue. A couple of other odd things (I believe) that might be indicators or could be contributing to the issue are that: The power seat only works (in the directions that do work) when the engine is running and the doors are closed. This may be correct operation but I would have thought that it would work any time the ignition is on and would not be dependent on the doors. The power window controls in the drivers door also inly work when the engine is running and all doors are closed. This could be unrelated but I don't think it used to do that and I think it only started at the point that the power seat failed. So my thoughts on this are that There may be a relay somewhere outside of the PSM that is triggered by the ignition that could be causing an issue. I don't have any of the wiring diagrams so can't tell. This might explain a link to the window controls if they run through the same relay A ground or continuity issue, this again might explain not functioning when any of the doors are open but it feels like it's a control law issue as it doesn't seem to be based on door position but more based on the closed sensors. A CEM/UEM fault. I'm not sure how the control laws work on the XC70 but the PSM doesn't work at all if the CAN connector is unplugged which suggests another controller on the CAN bus can enable/disable operation and maybe said faulty controller is giving false information to the PSM to stop moving the seat??? I've read a lot of posts on power seat issues but haven't seen anything the same as this. Hopefully someone has some ideas or has seen this before and can help. Thanks in advance.