MGf ABS Problem by carlpenn (Page 1 of 2)



carlpenn
Seeing as it isn't 75/zt related I am popping it in here.

Basically the MGf ABS (Antilock Braking System) Warning light doesn't come on when the Ignition is switched on, nor does it come on when driving. Checked Fuses, all ok.

So I unplugged the Modulator and the ABS Warning light lit up on the Instrument Display?

Anyone have any idea's? Could the Modulator be faulty ?
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Posted 24 Jun 2012, 19:17 #1 

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Duncan
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I assume both fuses check out? I only have circuits for the TF but I'm guessing they will be the same. Theres a 15A in the passenger compartment, and a big one underbonnet somewhere. Also worth checking the earths.

I did see one car where there was a problem with the ignition switch meaning there was no power to certain circuits, though I can't remember if ABS was one, though Epas was.

Edit: just had another look. According to the circuit diagrams, the ABS light couldn't come on with the abs disconnected as it's simply a bulb. At least thats what the TF circuits show. There have been some people switching bulbs around, to hide faults. Has it always done this?
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Posted 24 Jun 2012, 20:51 #2 


carlpenn
Duncan wrote:I assume both fuses check out? I only have circuits for the TF but I'm guessing they will be the same. Theres a 15A in the passenger compartment, and a big one underbonnet somewhere. Also worth checking the earths.

I did see one car where there was a problem with the ignition switch meaning there was no power to certain circuits, though I can't remember if ABS was one, though Epas was.

Edit: just had another look. According to the circuit diagrams, the ABS light couldn't come on with the abs disconnected as it's simply a bulb. At least thats what the TF circuits show. There have been some people switching bulbs around, to hide faults. Has it always done this?



Hi Duncan :)

It has done it since we bought it a few months back. The ABS Doesn't work so I know it is a fault, when it snowed I tried it on a quiet road with slush and the car skidded without the ABS Judder.

I do not understand how someone could change the Bulbs round? Do you mean swap the pins in the connectors? The Bulbs are linked through a Printed Circuit board on the back of the Instrument Panel.

When I disconnected the Wiring loom from the Modulator the light came on, so if it isn't coming on with the Modulator connected at Pre Ignition but when disconnected at the Modulator it comes on, then would I be right in thinking its something to do with the Ignition wiring as you mentioned?
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Posted 24 Jun 2012, 21:18 #3 

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Duncan
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Theres a few possibilities. It could be that the F and TF are different, it could be the workshop manual is wrong (it's more common than it should be) or it could be ignition wiring.

I'll do a bit more investigation into the circuit this evening.
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Posted 25 Jun 2012, 06:59 #4 


carlpenn
Duncan wrote:Theres a few possibilities. It could be that the F and TF are different, it could be the workshop manual is wrong (it's more common than it should be) or it could be ignition wiring.

I'll do a bit more investigation into the circuit this evening.



Thank You kindly Duncan :)
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Posted 25 Jun 2012, 18:00 #5 

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Duncan
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Well either the TF is too different, or it's someone been playing. On the TF theres a blue red wire that goes to pin 7 of one of the instrument pack connectors. According to the manual, one end of the bulb is supplied with 12v from the ignition switch, the other side is connected to the blue red wire. The ABS unit grounds this wire to switch the bulb on. So how it comes on when you disconnect the ABS is a mystery. Unless as I suspect, the system is too different. The F is an older model than the TF and the 25 that I also checked, though so it is possible there's a difference.

I may have some info buried somewhere for the F. I'll dig!
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Posted 25 Jun 2012, 18:18 #6 


carlpenn
Duncan wrote:Well either the TF is too different, or it's someone been playing. On the TF theres a blue red wire that goes to pin 7 of one of the instrument pack connectors. According to the manual, one end of the bulb is supplied with 12v from the ignition switch, the other side is connected to the blue red wire. The ABS unit grounds this wire to switch the bulb on. So how it comes on when you disconnect the ABS is a mystery. Unless as I suspect, the system is too different. The F is an older model than the TF and the 25 that I also checked, though so it is possible there's a difference.

I may have some info buried somewhere for the F. I'll dig!


Thank you so much for all this, I would not know where to begin looking.

I did find a Circuit Diagram for teh early F and it I will see if I can find the link again as I forgot to save it in my Favourites.

Here is one of them:

http://www.mgfcar.de/schedules/sb15.jpg

This one I looked at last night, but Electrical Diagrams make little sense to me !!

http://www.apttony.co.uk/Circuits/ABS.JPG
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Posted 25 Jun 2012, 19:15 #7 

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Duncan
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Well, F is the only one I don't have it seems.

However I've checked the 200 and 400 as well which are older than the F, and they are the same as the later cars. So unless the F is the only one that's different or the manuals are all wrong, I suspect either a faulty pack (can't see what the fault would be), or someones been changing wires around to hide a fault. I have seen that a few times now!

So I can only suggest: check the ignition feed wire to the ABS is getting volts (green pink, pin 15), the two big power connectors are getting volts (17 and 18 both brown pink), and the earths are OK (16 and 19 black). Pin 21 is blue red, to the instrument pack.

If you are still stuck, I can only suggest someone needs a look. If you could get to me I could try to help but I can't promise to fix it. The link to the F circuit diagrams would help too!
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Posted 25 Jun 2012, 19:26 #8 


carlpenn
Duncan wrote:Well, F is the only one I don't have it seems.

However I've checked the 200 and 400 as well which are older than the F, and they are the same as the later cars. So unless the F is the only one that's different or the manuals are all wrong, I suspect either a faulty pack (can't see what the fault would be), or someones been changing wires around to hide a fault. I have seen that a few times now!

So I can only suggest: check the ignition feed wire to the ABS is getting volts (green pink, pin 15), the two big power connectors are getting volts (17 and 18 both brown pink), and the earths are OK (16 and 19 black). Pin 21 is blue red, to the instrument pack.

If you are still stuck, I can only suggest someone needs a look. If you could get to me I could try to help but I can't promise to fix it. The link to the F circuit diagrams would help too!


Links above in previous post Duncan :)

I suspect someone has been messing with the Pack and possibly changed a wire as some of the Clips where broken when I was removing it for a look yesterday. Hopefully it is just they have switched a Wire or something simple. :)
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Posted 25 Jun 2012, 19:30 #9 

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Duncan
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Thanks for the links. The colours and pins are the same as other models. So either the diagrams are wrong, and the description of operation too, or someone has been messing.

Look for the blue / red wire at the instrument pack end, and see where it's connected. It should be in pin 7. If not then it confirms someone playing.

Edit: I would try it on my 45 to confirm, but the ABS modulator connector is impossible to get to without removing the fusebox.

Anyone else with an F fancy pulling the ABS connector and seeing if the light stays on?
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Posted 25 Jun 2012, 19:37 #10 


carlpenn
Cheers Duncan, Tina is at work tonight with the F so will probably be tomorrow night now :)
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Posted 25 Jun 2012, 19:41 #11 


carlpenn
Hi Duncan, Blue Red Wire is in Pin 5 and there is a Brown Orange Wire in Pin 7?
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Posted 27 Jun 2012, 17:35 #12 

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Duncan
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OK, I've looked at the links you sent again. The circuits are quite different. On the one I looked at, the circuits are pretty much the same as the F, and with the colours and pin numbers I quoted. However the blue red and brown orange aren't even in the same connector.

On the other site (the one that is scanned copies) the pin numbers are quite different. However I'm struggling to be sure what's going on as the scans are a bit unclear. I'll see if I can decipher them. To help me, how many connectors are there on your car in the instrument pack? Even better if you have some time, could you list the wires in each one as it will help identify them.
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Posted 27 Jun 2012, 18:10 #13 


carlpenn
There are two connectors. The one with the ABS Wire is listed below:


Wiring as follows:

1. Black
2. Yellow Green
3. Green Black (or Grey)
4. Blue Red
5. Green Red
6. Green Yellow
7. Brown Orange
8. Black White

These are listed in order as they appear and there is a small No. 1 at the Black Wire and a small No. 8 at the Black White wire.
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Posted 27 Jun 2012, 18:41 #14 


carlpenn
Found this Picture here and the one on the Right matches the one in my Car so can I assume the wiring is correct?

http://www.mgfcar.de/navi/instruments_cp_0091_1.jpg
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Posted 27 Jun 2012, 18:54 #15 

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Duncan
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OK, that's the connector, and the right wires in the right holes. The blue red is in 4 where it should be according to one diagram. Maybe the other link (which is easier to read, hence I used it) is for later cars, and I think yours is an earlier one.

There are certainly errors in the circuits I've found, so maybe there's an over simplification of the function of the warning that means it does come on when you disconnect it.

So now we know which diagrams to use, lets dig in!

You need to check two fuses. One is in a 'satellite' fusebox, which probably means a small group of fuses in a separate fuseholder clipped to the side of one of the others. It's a 15A fuse with a green pink wire. It connects to pin 4 of the ABS modulator. Check there is 12v on this pin with the ignition on. From what I can see it might be clipped to the side of the fusebox in the passenger compartment.

The other fuse is a big fuselink in the underbonnet box. Fuselink 2 which is 40A. This supplies pins 2 and 3 via brown pink wires, and both should have 12v all of the time.

According to the scanned circuits that are for your car they show the blue red wire goes to pin 40 but also pin 26. This is only shown on the instrument pack drawing, not the ABS one so I'm a little confused. There's a join in the wiring harness to let it do this and maybe that's something to do with the problem. Just check the blue red in the instrument pack is connected to both those pins in the ABS.

Last thing to check is the earths. There should be a good connection to ground on pins 1 AND 15 of the ABS unit. There should also be an earth connection to the body of the unit in the form of a strap.

I know its a lot to do, but it should help trace the problem!
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Posted 27 Jun 2012, 19:11 #16 


carlpenn
Thanks Duncan, will make a start :)
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Posted 27 Jun 2012, 19:15 #17 

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Duncan
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Oh! and of course, don't forget to check fuse 1 in the passenger compartment box (10A) as this is the supply to the warning lamp. Mind you other warning lamps would have failed, too. Should be 12v on pin 3 of the middle connector in that photo. Third pin from the right, green wire. The feed is the same as on pin 1 also green.
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Posted 27 Jun 2012, 19:19 #18 

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Duncan
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Just found the location of this satellite fusebox. It's clipped to the right hand side of the passenger compartment fusebox. Second one up, 10A

http://www.lame-delegation.de/mgfcar.de ... es_rhd.jpg
http://www.lame-delegation.de/mgfcar.de ... uses_2.jpg

Theres six of them in the little box. From top to bottom: 20, 25, 15, 15, 10, 10. Can you see where I mean? It's possibly even just been removed!
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Posted 27 Jun 2012, 19:25 #19 


carlpenn
I checked all Fuses and Earth Strap. All seems ok. So it is now to the more complicated stuff.
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Posted 27 Jun 2012, 19:51 #20 


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