Electric Seat ECU

In the last blog, we dealt with the rebuild of the switch pack and warned that if the controls still play up, the ECU would be the probable cause. In my own case, that is exactly what happened.
Before starting, purchase a new 3.5 volt 140 Ma battery – make sure it is one with THREE pins. namely TWO positive and ONE negative.(You can’t buy 100 Ma batteries any longer)
Apart from you usual tools, you will also need fine sandpaper, cheap white vinegar, cotton buds, some tweezers and a small soldering iron (I swear by the gas version – easier to control and no cable to get tangled)

Undo the main battery negative terminal – you do NOT want to fry anything.
The seat ECU is under the RIGHT HAND front seat – accessible from the rear. There are three different units under there and the one we want is the light-coloured box actually attached to the seat base itself. Do NOT mess with the others.
The first objective is to remove the unit from the vehicle. Start by feeling in the gap at between the box and the seat for a “twist” connector. This is usually only finger-tight and requires only a quarter-turn anti-clockwise to release it. Then the box will drop away from the frame.
GENTLY pull the connecting looms back to get better access to the box and connectors. A head-torch helps to see what you are doing in the confined space. Undo each of the multi-plugs – this allows the unit to come further away from the seat so you can see what you are doing.
Now for the worrying bit – with a Philips screwdriver, undo the two screws holding the two halves of the box together. Then ignoring the notice “this voids warranty” peel off the sticker and separate the two halves of the box. You will then see the BACK of the circuit board.
Carefully remove the entire board and wiring looms from the case. Turn it over so you can see the connectors. It is pretty obvious where each loom section plugs into the board but it never hurts to mark each one “A-A” “B-B” etc to avoid any confusion later. When all plugs have been removed, the entire unit will be free to move to the work-bench.

Now you are ready to examine and hopefully fix the unit:

The cause of failure will almost certainly be the leakage of the battery. With luck, it will not have damaged the circuit board beyond repair. With SMALL side-cutters, snip the THREE pins holding the battery to the board. Do this as close as possible to the battery itself leaving as much of each pin attached to the board. Electronic experts will argue about this because they will probably prefer to un-solder the pins from the board but the cutting technique make the positioning and soldering of the replacement battery much easier.
With the battery removed, examine the board carefully. There will probably be a whitish deposit all round where the battery leaked. The deposit may also be on the adjacent components – especially the IC chip and/or a condenser or resistor. These deposits MUST be neutralised.

Using a cotton-bud, swab the area with plain white vinegar Рa mild acid that will neutralise the alkaline from the battery. Rinse away the vinegar with water and GENTLY dry the board with air (a hairdryer on low setting is good). Scrape any residual deposits off with very fine sandpaper and blow it clean.
Now examine it again- it will be obvious if the board and/or components are beyond repair. The copper tracks on the board may still look damaged but they can often be cleaned with sandpaper. Do NOT cut into the board – just remove all of the gunk and oxidization. When it is all clean, give it a LIGHT coat of nail polish (Gee, thanks Juliette, I will return it, I promise).
CAREFULLY bend each pin you cut off earlier and position the new battery so all pins are nicely aligned, just touching the battery. (Now you know why you cut them high). Use FINE resin-cored solder to solder each of the three pins to the battery. Examine each joint carefully so ensure you have good joints but no solder anywhere you do not want it.

BEFORE you replace the board into the box, (you can do this after it is back in the vehicle) it is real smart to return it to the vehicle, replace ALL of the plugs, replace the main battery negative terminal and test to see if the seat switches now work. If not, you have either messed something up OR the board/components were damaged beyond saving. However, all you have lost is $20 for the battery and a few hours work. If it all works, SMILE – you have just saved $1000 for a new ECU and several hours of expensive workshop time


This picture shows the refurbished ECU – note the new battery in the top right corner. The wiring plugs have been replaced and the unit is ready for testing.


Remember that a NEW ECU costs around $1000 plus labour. If this procedure is beyond your skill level, at least you now know what is involved and Grahame Cooper Automotive has arranged with this author to do the job for you at a cost of $250 per board, plus postage.
Terms are as follows:
1) A deposit of $125 is required at the time of commencing work
2) The motors must have been hot-wired AND the switch pack must have been tested and/or repaired first to eliminate these items as the causes of the problem
3) When we examine it, If it becomes obvious that the board is damaged beyond repair, there will be NO charge and the deposit will be refunded
4) Even if the seat motors work afterwards, there is NO guarantee the memory functions will work

Please contact Craig (parts@graemecooper.com.au) if you want us to do the work for you