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Discussion Starter #1
Hi all hoping someone can help. So I've got a 2005 147 jtdm lusso with factory fitted leather heated seats none of which are working. So obviously since neither work my first port of call was the fuse which looked fine but I replaced anyway. Still nothing so then I took the fuse out and checked the socket with a multimeter first with just the power on then with the engine running. Still no power getting to the fuse. So checked the only other thing I could think of relays. All working there yet still no power to the fuse. I've checked other fuses such as electeic windows and radio to see if maybe it's my multimeter but they all get power just fine. So at this point I am baffled does anyone have a clue what might be going on ?
 

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Discussion Starter #3
Not sure which fuse in the engine bay it is but they only seem to go up to 60 also that diagram lists a 30 amp in the wash fuse box but the owners manual says 15 amp. I did also find somewhere that the largest relay in the wash fuse box was fornthe seats but this also appears to do the windows which work fine so not sure. So pic one is the engine bay fuse box in front of the battery and pic 2 is the dash one from my understanding the heated seat fuse is the 15 amp one 3rd down far right (this gets no power) and the relay is the largest one at the bottom under the 2 red ones. I could be wrong
 

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yeah, in the schematic, you can see power to seats is via F45, 15 amp.

from elearn:
Description
The front seats may be optionally fitted with a special heating system (consisting of two heater elements located in the cushion and squab): these heat the seat to ease the discomfort of entering a cold passenger compartment in very cold weather, e.g. when the car is left outside for long periods during winter.

The heating device located in each seat consists of two resistors operated by a switch located on the outside of each seat.

Once a certain temperature is reached, the heating action is automatically cut off by a thermal contact inside the device.

An LED located on the button itself indicates when the resistors are switched on.

The circuit is controlled by the services relay and is protected by a specific fuse, both located in the unit under the dashboard. The heating is switched on both when the ignition is on and when the ignition is off.

With the ignition on during starting, this relay is temporarily deactivated.

With the ignition off, the Body Computer keeps the relay activated - which also supplies the door mirrors and electric windows - for 3 minutes, but deactivates it immediately when one of the two front doors is opened.

The switching on of the resistors is disabled if the battery voltage is less than 10 V.
 

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Discussion Starter #6
Ok so just had a look. Battery is 12.5 (engine off). Found the correct fuse in the engine bay, nothing wrong there. Confirmed it was the correct fuse by taking it out and checking the windows (since they use the same relay as the heated seats) with the fuse out windows did not work And with it in they did. So engine bay fuse is good, battery’s is good and relay works on the windows yet still no power to the 15 amp f45 fuse. So is it possible the ecu just isn’t activating that function because it has forgotten it has heated seats installed (seems unlikely as dont think it works like that but I’m no expert) or does the relay have multiple switch circuits and the window one works but heated seat circuit has gone (is this possible). If nether of those is the case then I guess only other thing would be something burned out in the fuse box itself (again seems unlikely but not impossible). Is there anything new else I’ve missed?
 

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Reading that if I understand correctly the BCM energises the services relay this must be happening as windows etc work.
Not seen the circuit but the power from relay does it go directly to the fuse or does it go via a dedicated heated seat relay that the switch energises which would then put the feed via the fuse to the seats?

As there is a thermal cut out in the heater pads I would suspect a dedicated relay,but you will need a drawing to determine the set up of the circuit.
 

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Discussion Starter #8
Yeah, you would have thought there was a dedicated relay but judging by the schematic it just goes from the services relay to the f45 fuse and from there directly to the seat switches which are then both grounded together. I wonder since both seats are grounded together if my problem may, in fact, be a bad earth? does anyone know which wires do what on the switches? I assume the 2 red wires are power and the switch when active connects these 2 together but then there's brown and black one of which will be earth just not sure which and whats the other? being a 2 door it's possible that the earth wire may have been damaged over time due to the seats sliding back and forth although i'm only the 3rd owner and don't think the back seats have been used all that often but hey never know
 

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..... does anyone know which wires do what on the switches? I assume the 2 red wires are power and the switch when active connects these 2 together but then there's brown and black one of which will be earth just not sure which and whats the other? ....
The wire colours are mentioned in the schematic (post #2), see https://www.alfaowner.com/Forum/alfa-147-156-andamp-gt/65864-wiring-colors.html for colour codes.....

The fact that there is no additional relay for the seat heaters is one of the reasons quite a lot of people report defective switches on the seat heaters (high current)
 

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If that’s the set up of the system then I would be checking the wiring between services relay and fuse 45 as you already mentioned no power there.
I wouldn’t bother with the grounds yet until you sort out the power side as even with good ground they still wouldn’t work.

You able to post picture of the circuit diagram?
 

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Discussion Starter #11
hmm still seems odd as even if the switches were defective or the earth was bad I should still surely get 12v being supplied to the switch if I test with the multimeter earthed to a good earth point on the chassis. a bad switch would just prevent the 12v from getting to the seats themselves. As it stands no power is getting to any part of either switch. I have unplugged them and tested the wires coming in. it does seem to be that somehow nothing is getting from the relay to the fuse and so nothing gets to the seat switches but there's nothing else between the relay and the F45 fuse. So this week when I get a free evening I will check the earth and general condition of wires under the seats and then take off and test the switches and hopefully find something. I would say that if there is a bad switch or a bad earth then its possible the electricity wouldn't travel up to the switch (based on the principle of electricity taking the path of least resistance) but then if I'm testing with the multimeter on a good earth I am compleating the circuit and therefore should be getting 12v on the feed to the switch. hmm ill check the condition of all the wiring related to the seat heaters and report back.
 

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Discussion Starter #12
If that’s the set up of the system then I would be checking the wiring between services relay and fuse 45 as you already mentioned no power there.
I wouldn’t bother with the grounds yet until you sort out the power side as even with good ground they still wouldn’t work.

You able to post picture of the circuit diagram?
There's a diagram on post 2. since the relay and fuse 45 are plugged into the same fuse board (in Dash) I guess I need to take the fuse box out and have a look at the back of it to test the connection between the relay and fuse right?
 

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Very simple circuit then that is, you have power to the common on relay (30) assuming you have power out of switched side (87) as other electrics like windows or mirrors can’t remember which work? Which suggests the feed out is linked to more than one fuse in the cabin fuse box. As you have no power to fuse 45 this suggests the problem is within the fuse box area.

I would leave grounds,switch alone and also wiring under seat as fault is on the supply side of fuse 45 is dead.
Unless of course it is a double pole relay? A look at the circuit drawing for the other circuits powered by services relay will confirm if they are supplied via 87 or a different contact?
 

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Just for clarity, I've enclosed the circuit with the relevant bits enlarged.
I'm sure you've taken this into account, but of course you will only see power on fuse F45 if the services relay is activated ......
P.S. just for info, windows are also powered via pin 87, and two 20 amp fuses (F47, F48) on the same services relay.....

if there is indeed no power on F45, with services relay activated, I would indeed look at the back of the fusebox, to see if there is a problem there (burnt trace f.i. ?)
 

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other thing you could try of course is, with relay pulled, measure continuity between pin 87 of relay socket and one of the pins of Fuse F45 ......
 

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Discussion Starter #16
Just for clarity, I've enclosed the circuit with the relevant bits enlarged.
I'm sure you've taken this into account, but of course you will only see power on fuse F45 if the services relay is activated ......
P.S. just for info, windows are also powered via pin 87, and two 20 amp fuses (F47, F48) on the same services relay.....

if there is indeed no power on F45, with services relay activated, I would indeed look at the back of the fusebox, to see if there is a problem there (burnt trace f.i. ?)
Yeah, ill test the continuity later. if it is a burned out trace I'm hoping the box is not too difficult to get out. I'm fairly good at fixing wiring and soldering so should be able to fix it if it is that. would be odd for it to burn that out but not the fuse but then it wasn't working when I bought the car so maybe it did blow the fuse as well and the previous owner replaced the fuse. either way, I'll check it out later its a silly little thing as being the middle of summer it's not like I need heated seats right now but its currently the only thing on the whole car that doesn't work so being the enthusiastic tinkering type I'm straight in there lol
 

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Yeah, ill test the continuity later. if it is a burned out trace I'm hoping the box is not too difficult to get out. .....
it's not too difficult, couple of screws and connectors.
You'll find a number of descriptions on the forum, as the bodycomputer is mounted on the back of the fuse panel, and people regularly need to access this... ;)
 

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Discussion Starter #19
Ok so update. I’ve got myself a better multimeter with continuity buzzer and checked the connection between pin 87 and the f45 fuse. Connection there is good so checked the fuse that’s also good. So then tested between the two terminals the fuse plugs into and absolutely nothing so I think that’s the problem bad connection on the fuse holder will hopfully have time on Thursday to investigate further
 

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Discussion Starter #20
Actually no there wouldn’t be a connection there as the fuse is the connection so I actually need to check the wiring from the fuse to the switches
 
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