Power Seat Question

[John Gustafson]

The passenger side power seat on our Volvo 850 (95) stopped working properly
a couple of weeks ago. It would recline the seatback but would not move it
back up (each time the switch was pushed it only moved a small fraction).
My mechanic (who I've used for some time and trust) diagnosed the problems
as a faulty seat switch. $400 later, the switch now brings the seatback up,
but not all the way. We can get it all the way up by repeatedly pushing the
button, but it will not raise all the way up in one motion. The interesting
bit is that the seat moves smoothly up to the up right position when using
the memory buttons (e.g., once we had it up we stored that position in
memory).

I'm clearly going to take it back to my mechanic and have them complete the
repair, but thought I would ask the group if any one has had a similar
experience and if so, what the problem and final solutions where.

Thanks,

Gus

 

[Gus]

We did have a similar problem on the driver's side that was the 'known'
cable problem (about $140 to replace). This time the seat does move, so I'm
fairly sure it is not the cable. It behaves more like the override switch
(that stops the seat when it runs into something) kicks in early. Anyway,
thanks for the input and advice.

John

 

[K Bourke]

Had the same problem win my '93 850, and was advised it was the "known cable
problem" ....

Turned out to be the resistor/potentiometer as Bob describes, and resulted
in a *much* cheaper/easier fix.

Kevin

 

[volvowrench]

I'll give that a whirl. I wonder if I can get some of my $400 back from the
mechanic for an unneed repair. Any idea how the seat "unlearns" the proper
position or was the initial problem the seat switch and the mechanic just
didn't reset the set position detector? Anyway, thanks for the advice.
I'll let you all know if this works.

Gus

The control unit measures the load on the motor. When the seat is run all
the way back until it begins to compress the rear seat cushion, the load
goes up dramatically. The control unit measures the resistance across the
linear pot at that point, calls that one end point and calculates the
other end point based on a preset value for degrees/ohm up to a design
standard of whatever it is (120-135 degrees, I would guess).

Since the old value remains in memory the seat back stops prematurely. By
forcing the seat forward a little bit at a time you extend the forward
limit. Kind of like sliding a tab on an old typewriter.

Bob

 

[Tony Rairden]

I just had the seat back angle adjust on my '95 854T fail; my Used Volvo
specialist dealer (JR's Vovo [sic, due to Volvo's lawyers...] Sales in
Louisville, KY) diagnosed it as cable breakage or disengagement... I'm
hoping for the latter... (I guess I may be better off with a non-power pax
seat than with both power...)

Tony Rairden

 

[Tony Rairden]

When the limit switch "learning" is the problem, does the motor run at all?
I can hear it (different pitches for up and back) when I hit the switch,
which makes me think cable disengagement or break rather than limit switch
malfunction...

Tony Rairden