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None functioning drivers power seat 900 1994

posted by yankee on Sat Jan 28 22:53 CST 2012
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last visit: Thu Oct 16 10:27 CST 2014

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Ok all you power seat guru's. First a little history. Pulled the drivers seat out of the car and replaced the drive cable for the forward and back motor. Tested it and everything worked, back and forth, tilt and recline. My daughter gets in the car moves the seat forward now nothing works. I checked the fuse and it's fine checked connections and they are good, test for power with my multi-meter and that's fine. I also sprayed some contact cleaner into the switches but still nothing.. Could it be the little computer for the memory or the switches. None of them work now... Help please..

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None functioning drivers power seat 900 1994

posted by spook on Sun Jan 29 06:50 CST 2012
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last visit: Fri Oct 24 08:06 CST 2014

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Dear yankee,

Hope you're well. Before pulling the seat, I hope you disconnected negative battery cable terminal from the negative battery terminal. This cuts power to the SRS sensor, affixed to the floor pan under the driver's seat. Cutting power avoids risk of accidental airbag deployment, should seat be dropped onto sensor. Airbag deployment can be lethal at close range. When removing a driver's seat in a 940/960, the SRS system must be made safe, by disconnecting the negative battery cable terminal and waiting 20 minutes (for SRS system capacitors to discharge).

I'd re-check the seat's power connector (gray housing, at front end of door-side seat rail) and connector from the switch to the seat computer (green housing), to be sure they're fully seated.

If memory serves, there's a relay in the seat switch, that protects the computer against a power surge. If present, the relay's case is black plastic (about 3/4" long, 1/2" wide).

There is also a relay - open frame (not encased in plastic) inside the computer, on the side of the circuit board, nearest the power connector. If either relay has failed, power won't (a) get from switch to the computer or (b) from the computer's power input, to the six smaller relays that allow power to flow to the motors.

You can use a voltmeter - and a portable 12-volt source - to find out if power flows past the switch. If power reaches the computer, you should be able to see/hear the main relay operate, when you move one of the seat switch function selector levers. If the computer's main relay does not work, the computer will have to be replaced. Volvo does not supply the relay, only the entire computer.

Hope this helps.

Yours faithfully,

Spook

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None functioning drivers power seat 900 1994

posted by yankee on Sun Jan 29 13:33 CST 2012
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last visit: Thu Oct 16 10:27 CST 2014

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Dear Spook
Good to here from you... I checked the white connector cleaned the contacts check to see if I'm getting power through the connector and saw a good 12 volts.. Funny thing is that with the switch failure started with recline position then tilt then forward and backyard failure. If it was a relay wouldn't switch fail all at once??? I did pull the switches away from the the seat but all I saw was the circuit board. I didn't go any further then that..I can see under the seat and check connections and they all seem solid..

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None functioning drivers power seat 900 1994

posted by spook on Sun Jan 29 13:38 CST 2012
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last visit: Fri Oct 24 08:06 CST 2014

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Dear yankee,

Hope you're well. Your first message suggested the failure was sudden and total. That is, after the seat motor was replaced, your daughter moved the seat forward, and then everything suddenly stopped working.

When you move the switch levers, do you hear the motors running? Or, is there only silence?

If the motors are running, but the seat does not move, the drive cables are not properly positioned.

If the motors stopped turning one-after-the-other, the problem most likely is in the seat computer. Had the switch's relay failed, all motor function would have been lost at the same time.

Hope this helps.

Yours faithfully,

Spook

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None functioning drivers power seat 900 1994

posted by yankee on Sun Jan 29 14:39 CST 2012
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last visit: Thu Oct 16 10:27 CST 2014

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Sorry for the confusion I had to interpret my daughter's conversion then did my own trouble shooting. Motors all three of them do not run.. Now how difficult is the board swap??

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None functioning drivers power seat 900 1994

posted by spook on Sun Jan 29 20:05 CST 2012
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last visit: Fri Oct 24 08:06 CST 2014

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Dear yankee,

Hope you're well. First thing to do is to see if 12 volts arrives at the computer. If it does, but if the main relay does not work, then the computer has failed.

The seat computer's circuit board is not available from Volvo, so far as I know. The entire computer must be replaced, unless you have: (a) the means to trouble-shoot the circuit board and (b) a source of replacements for circuit board components.

The part is #9128546. New from Volvo, it is about $300. I'd guess you could find it at a salvage yard for a fraction of that.

When you remove the driver's seat, be sure to remove the negative battery cable terminal from the battery terminal. Wait 20 minutes. You will then not be at risk from the SRS (airbag) system.

Hope this helps.

Yours faithfully,

Spook

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None functioning drivers power seat 900 1994

posted by yankee on Mon Jan 30 01:08 CST 2012
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last visit: Thu Oct 16 10:27 CST 2014

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Where is that relay located???

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None functioning drivers power seat 900 1994

posted by spook on Mon Jan 30 06:53 CST 2012
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last visit: Fri Oct 24 08:06 CST 2014

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Dear yankee,

Hope you're well. If you refer to the seat computer, see my prior post. The relays inside the seat computer are "open frame": they are not encased in plastic.

On the seat computer's circuit board, the main relay is close to where the cable from the seat switch enters the computer housing. The main relay protects the circuit board. On the opposite side of the sat computer's circuit board are six smaller relays. These smaller relays control the flow of power to the seat motors.

Hope this helps.

Yours faithfully,

Spook

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