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850/x70 S1 Articles How to's and step by step guides on a specific repair or modification to a Volvo 850/70 car.

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Electric seat diagnosis

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Old Jun 16th, 2018, 00:15   #1
SwedishBus
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Default Electric seat diagnosis

The electric seat on the V70 and similar with the memory function is fairly easy to diagnose when it fails. The faults that are likely to occur fall into two broad catagories;
1) Faults with the motor/s and associated harnesses
2) Faults with the switch panel and associated harness

There is, of course, the possibilty that a fault could have occurred in the control module under the seat, however this is much more unlikely than a straightforward electro-mechanical fault elsewhere on the seat, so unless all other avenues have been explored, it's not worth swapping-out the module. Likewise, if the power to the seat has failed at the fusebox, etc., then that will need dealing-with first.

To narrow the two categories down, a few tests of the switch panel are required;

a) Does the seat move with any switch input at all? If not, then check the fusebox and the supply +12v and ground to the seat module first, before stripping the switch panel out for further tests

b) Does the seat not move on one or more switch inputs, but otherwise moves if the Memory buttons 1, 2, 3 are pressed? Again, the seat switch panel needs stripping out and repairing.

c) Does the seat not move on some switch inputs, but a clicking can be heard from under the seat on those failed movements? This is more likely to be the motor/s within the seat, requiring the seat itself to be stripped down. If the backrest angle function is the failed movement, this can be done with the seat in-situ in the car, otherwise it is going to be easier to remove the seat completely in order to repair it, as the raise/lower and forwards/backwards motors are all underneath the seat cushion - very tight to access for motor removal.
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Old Jun 16th, 2018, 01:52   #2
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Default Electric seat switch-panel removal

Assuming that the seat is making no clicking noises, the switch panel is the likely area of failure in the V70 electric seat. It is fairly exposed to the weather when the door is open, but also incorporates some fragile (in old age) circuit-board electrics. As I will explain later in this thread, there is one specific area that is likely to fail in old age, which is very easy to repair with a soldering iron (small tip circa 1mm required), some solder, and a little time. You will also need a 12v test-lamp with its own built-in battery for continuity testing (a 12v battery, some wire, and a 12v/5W sidelamp bulb will make a good tester), or a simple electrical meter with a Resistance function will suffice.

The first job is to safely remove the switch panel from the side of the seat. There is no need to disconnect the main vehicle battery for this work, though caution is needed to ensure that all correct procedures around the airbag system are adhered-to. It will help with diagnosis and confirmation-of-repair if the seat module is otherwise left powered-up, which is its normal state with the ignition key in the "OFF" position, or even out of the column.

The main thing is to make the seat panel as easy to maneouvre as possible, so that means disconnection of the green multiway plug on the front of the seat module that feeds the harness going across to the switch panel. Volvo have chosen to make thsi plug as fiddly to remove as possible; the latch that needs to be depressed into the plug to release it from the module is facing down towards the module mounting panel. A small digit can just squeeze into the gap to push the latch whilst the plug is gentle wiggled free.

Release any tie-wraps securing the harness to the seat frame.

(see photo 1) Lift the front-facing edge of the switch panel straight upwards to release it from the airbag trigger housing, then knock it backwards towards the rear seat to disengage it from the seat tubular piece near the seat buckle. IT IS IMPERATIVE THAT THE SEAT SIDE AIRBAG TRIGGER IS NOT ACCIDENTALLY PUSHED TOWARDS THE SEAT CUSHION DURING THIS STAGE.

As soon as the switch panel and seat trim surround is loose from the seat, carefully remove the inhibitor (orange coloured) plastic piece from its stowage under the trim panel, and insert it between the inner and outer parts of the side airbag trigger unit. Do not knock or accidentally push the trigger face towards the seat. Once the inhibitor piece is in place, things are much safer to work-on.

The switch panel can be removed from the seat side trim panel on the workbench. There are three screws (Torx T20) securing the switch panel. The tie-wrap securing the harness to the seat trim near the airbag trigger clipping area will need to be cut to release the harness. It is important on reassembly to renew this tie-wrap, as it prevents the seat switch harness from fouling the airbag trigger unit.

(see photo2) Release the plastic latch at one end of the switch panel, and push the panel upwards (in its normal, fitted orientation in the car) out of the trim. It might be a bit tight on its dovetailing, but it will just slide out. Guide the harness through the trim, and then the module connector plug.

The switch panel can be further dismantled by removing 8x screws securing the circuit board to the switch front panel. Note that two (ringed) are also cord-grip screws. It is important that the switch buttons are facing down towards the workbench, and stay in that orientation during this work. There are four tiny springs (yellow-ringed in photo3) that will escape from the memory buttons if the panel is inverted, then there will be fun trying to find then, let alone feed them back into the buttons. Just work with the circuit board facing upwards towards you.

(see photo3) The main concern on this circuit board is the harness connection plug that is header'd onto the circuitry (red-ringed in photo); the joint is mechanically loaded, and the solder cracks. It is obvious from each of the microswitch units where the circuits go, and the best test is to operate the switches in turn and measure the continuity to the common 12v feed to them. This is the main circuit around the outside of the circuitboard, it is fed by the Orange and Blue wires in parallel to each other (either will work as a test-point). If the header solder joints have both failed on these two wires, then all switch functions will cease to work, hence this switch panel is a valid part of the overall seat diagnostics after a fusebox check for supply voltage. The wire colour that feeds the main seat module (pin_1 on plug A) is a Green with a Red tracer, and this should have 12v on it permanently when the car is "awake" with the doors open.

All the microswitches have a unique wire colour which should show good continuity to the Orange or Blue wires as each is pressed. Note that the switch contacts are made on each unit in the opposite direction to that which the switch is pushed. The functions and their wire colours are;

Forwards - Red wire
Backwards - Black wire
Rear raise - Yellow/white wire
Rear lower - Orange/white wire
Front raise - Brown/white wire
Front lower - Red/white wire
Backrest raise - Violet wire
Backrest lower - Green/white wire

(see photo4) It is likely that a close inspection of the header joint for the harness plug has broken (cracked or "dirty" looking solder) joints on one or more pins (see close-up photo). To rectify this, the joint should be heated with a fine-tip iron, wiped clean of old solder (an old cloth will suffice), the joint fluxed slightly, and new solder added back into the joint. The important thing is to work progressively through all the affected joints in turn, and avoid bridging across between the pins with solder that is being removed/added.

Reassembly, as they say, is the reverse of disassembly, but it is well worth doing a series of checks before putting everything back. Firstly, check for continuity between all adjacent pins - there should be none, except the diagnostic resistance pins with the Yellow and the Grey wires - that is normal. Secondly, assemble the switch button panel back to the circuit board, then plug it into the car and check that everything is now working - don't panic if it doesn't, as if the switches have been duff for a while, there is a chance the motor/s have seized in the meantime from lack of use. That is a further repair!

Remember to secure the harness lead inside the seat side trim over the airbag trigger moldings (that clip the trim down over the airbag trigger) with a new tie-wrap, and leave the harness plug loose whilst the switches/trim are refitted to the seat - it will lessen the chance of the airbag trigger being pushed accidentally once the orange piece has been removed and re-stowed. Locate the trim panel first over the tube at the rear edge of the seat, ensuring the seat buckle is clear of the area, then lower the front of the trim panel squarely over the side airbag trigger housing, and push downwards to latch.

If the seat motors need investigation, that is to be continued....

Apologies for lack of photos - forum is having difficulty uploading these right now. To be added later.
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Old Jun 16th, 2018, 11:49   #3
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Brilliant, SwedishBus, great write up so far! Many thanks in advance for going to such lengths!

If you're having difficulty uploading pics it could be that they're too big...? Do you have a means to resize them such as Microsoft Office Picture Manager or Image Resizer for Windows?
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Old Jun 17th, 2018, 00:37   #4
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Originally Posted by Baffler View Post
Brilliant, SwedishBus, great write up so far! Many thanks in advance for going to such lengths!

If you're having difficulty uploading pics it could be that they're too big...? Do you have a means to resize them such as Microsoft Office Picture Manager or Image Resizer for Windows?
Hi Baffler,
Yes, I had already resized them down again - I normally resize photos for other forums to 450kB max, but I see this forum needs them much smaller. There are four shots that are around 250kB apiece, but I will double-check that the pixel count also meets the forum requirements.

To be frank, I'm probably struggling because of my geographic location; we are the land that time forgot as far as broadband is concerned - as well as any governments!

I'll keep trying, as a picture speaks a thousand words, and I'll do the write-up on the seat motor repair ASAP. If you are having trouble with your base motors, that is the fore/aft slides, and the cushion raise/lower functions, then the seat/s will need to come out, as I think motor access is just too tight against the floorpan.
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Old Jun 17th, 2018, 00:46   #5
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Photo_1 Switch panel removal;
D5252T_seat_switches_removal.jpg

Photo_2 Switches being dismantled;
D5252T_seat_switches_dismantle1.jpg

Photo_3 Switches exposed for working-on;
D5252T_seat_switches_dismantle2.jpg

Photo_4 Detail on dry-joint inspection;
D5252T_seat_switches_dryjoint.jpg
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Old Jun 18th, 2018, 10:40   #6
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Originally Posted by SwedishBus View Post
Hi Baffler,
Yes, I had already resized them down again - I normally resize photos for other forums to 450kB max, but I see this forum needs them much smaller. There are four shots that are around 250kB apiece, but I will double-check that the pixel count also meets the forum requirements.

To be frank, I'm probably struggling because of my geographic location; we are the land that time forgot as far as broadband is concerned - as well as any governments!

I'll keep trying, as a picture speaks a thousand words, and I'll do the write-up on the seat motor repair ASAP.
That would be great! Thanks so much, SB! Pictures are indeed invaluable

I see you and others have managed to attach them directly to the page as opposed to a thumbnail...what option does one need to select in order to make them appear like so?


Quote:
Originally Posted by SwedishBus View Post
If you are having trouble with your base motors, that is the fore/aft slides, and the cushion raise/lower functions, then the seat/s will need to come out, as I think motor access is just too tight against the floorpan.
If I remember correctly it was only the drivers fore/aft and passenger backrest that nothing was happening...all other functions were there so I'm hoping it's just a bad solder joint in both cases. I had managed to remove both front seats for inspection, removed and stripped the drivers control panel and gave it several blasts with contact cleaner but never thought to inspect and solder the joints

I'll get another look later in the summer as we only just bought the car early last July so my priority was to get it 100% mechanically for its trip across Europe. Never missed a beat, by the way, but do you know what makes this thread even more interesting...it was originally registered in Sweden making it a proper Swedish Bus
Attached Images
File Type: jpg LHD V70 3.jpg (306.3 KB, 10 views)
File Type: jpg LHD V70 2.jpg (375.9 KB, 5 views)
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Old Jun 18th, 2018, 23:53   #7
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It sounds like you need my next stage of the post!

I am sure, from your description, that your problem is a dirty commutator and/or brush-box on the seat recline motor.

This is the one motor you can do with the seat in-situ, and is not a bad job to do at-all. The motor will have to come out onto the bench, but once you have it loose, I reckon you could fix this in 40minutes.

I'll try and get the next bit uploaded ASAP, but in the meantime, double check whether you are getting a distinct "click" when you try to operate the seat recline button in either direction. If you are, job is in the motor or its wiring from under the seat. If not, then the job is likely to be in the circuit board and wiring header as I described above. Good luck!

PS. Your car looks great in the thumbnails, and your seats are certainly in far better condition than mine. I have only had my second V70 (TDI) for 4weeks as a "wrecker", but it has potential - if it behaves itself after its engine rebuild!
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