ECU "Brake switch" error - Alfa Romeo Forum
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ECU "Brake switch" error

It never rains but it pours. Just put the clutch back together with a new release bearing in the GT and I have ABS and VDC Failure warnings on the dash at switch on: my "ASR Off" light is also on as might be expected.
I have a single fault showing in both the engine and ABS ECUs and that is Brake Switch. I know the brake pedal switch is working - at least partially- because the brake lights work. So does this mean there is some other kind of pressure sensor/switch somewhere in the system I could have disturbed during the gearbox removal and replacement, it seems too coincidental that the fault started exactly after I changed the clutch to not be my fault but I certainly didn't go anywhere near the brake pedal.

Infamy, Infamy, They've all got it In For me!
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If it's the same switch as used on 147s it will have two pairs of contacts, so it's possible for the brake lights to work properly with a faulty switch. If one pair of contacts is faulty the ECU is seeing conflicting signals - it sees the brake pedal pressed & not pressed at the same time.

It is possible to dismantle the switch & clean the contacts but as it's a very cheap component it's better to buy a new one & cure the problem long-term.
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[QUOTE=Dave Brand;15358050]If it's the same switch as used on 147s it will have two pairs of contacts, so it's possible for the brake lights to work properly with a faulty switch. If one pair of contacts is faulty the ECU is seeing conflicting signals - it sees the brake pedal pressed & not pressed at the same time.

That's a sensible conclusion and I wish it were so easy ( maybe in a ford or Rover even it would be ) however both "sides" of my switch ie contacts 1 to 3 and 2 to 4 are working according to the resistance testor, also according to ELearn as best as I can make out contacts 2 & 4 are the ones that send to the brake lights and the ABS! 2 & 4 are for cruise control where fitted.

This is of some use as it tells me that the fault is not with that switch it's self but the signal from it IF ( as per my original question,) it is actually that switch to which the fault is referring; if that is the case however the signal must be getting as far as the body computer which controls the brake lights; but not as far as the ABS/VDC controls
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Try the clutch pedal switch.
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by that you mean try swapping the clutch and brake pedal switches?
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by that you mean try swapping the clutch and brake pedal switches?

why that posted twice i'm not sure. twitchy finger? anyway since it has- I'm guessing you mean to see if the clutch switch is working better
if not let me know what you did mean. I haven't tried that this evening as it's got too dark now but I have a new spare switch in the garage I'll try and if that's no improvement ill try the clutch as it's only a couple of minutes work; however as pointed out earlier the continuity tester has already indicated that the switch is working and the brakes coming on when it's pressed would seem to back that up so I'm not confident i'm going to get much further doing it.

BTW I've done my homework and I'm aware that here are a few old threads on here about people finding this happens after they have problems with the reversing light or it's switch and my reversing light did stop working after a recent heavy storm The reversing light is still refusing to work even though the fuse, bulb and switch have all tested good. but sadly non of the relevant fuses have been found to be blown, ( particularly the one shared with the ABS ) I suspect corrosion in the socket is preventing a good contact. so whilst Im open to other ways it could affect the ABS haven't linked the two yet.

Last edited by Yorkshirekeith; 21-10-16 at 13:39.
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Quote:
Originally Posted by Yorkshirekeith View Post
by that you mean try swapping the clutch and brake pedal switches?

why that posted twice i'm not sure. twitchy finger? anyway since it has- I'm guessing you mean to see if the clutch switch is working better
if not let me know what you did mean. I haven't tried that this evening as it's got too dark now but I have a new spare switch in the garage I'll try and if that's no improvement ill try the clutch as it's only a couple of minutes work; howeveras pointed out earlier the continuity tester has already indicated that the switch is working and the brakes coming on when it's pressed would seem to back that up so I'm not confident i'm going to get much further doing it.

BTW I've done my homework and I'm aware that here are a few old threads on here about people finding this happens after they have problems with the reversing light or it's switch and my reversing light did stop working after a recent heavy storm The reversing light is still refusing to work even though the fuse, bulb and switch have all tested good. but sadly non of the relevant fuses have been found to be blown, ( particularly the one shared with the ABS ) I suspect corrosion in the socket is preventing a good contact. so whilst Im open to other ways it could affect the ABS haven't linked the two yet.
hoping you can diagnose whats wrong with your car, mine does the same thing but on a 147 gta. multiecuscan said it was the brake switch so I replaced it with a new one. Still have a random failure coming on the dash every trip after a few hits on the brake or sometimes straight away, restarting the car gets rid of the warning only for it to return at some point later in the trip. I have put up with it for a few years now and it only becomes an issue when going for an MOT if I get a non Alfa friendly tester. I have cleaned all contacts in the system that are obvious with contact cleaner and checked all earths, even a new battery recently didn't fix it.
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Hi Growler. Well I'm trying but I have to say our symptoms aren't exactly the same. Mine has been 100% consistent since it started after I put the gearbox back in; I have had the ABS failure followed by VDC failure alerts as soon as I turn the key without even having to press the brake pedal, every single time I've turned the key. In a way that's good as it means I'll have to fix it and should know for certain when I have, I sympathise with you as I hate intermittent faults ( like my Airbag light ) which you think you've sorted but then decide to come back and taunt you the night before your MOT! ( did that sound like the bitter voice of experience )

It's because It started straight after I'd been pushing that gearbox about in the engine bay that I suspect I've knocked a connector or chaffed a wire or something.

BTW does anyone know if connector D097A or D97a ( short circuit connector ) along with it's two conjoined friends on Elearn is on the engine or cabin side of the bulkhead because that is one of my main suspects and I can't find it!!
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I'm wondering if the culprit is in fact the brake pressure sensor.

I believe D97A is up behind the dash, on the right - not in the engine bay. I think it's labelled on the top of itself "3+3+3" and this is D97 A/B/C in essence. My experience has been that save for physical damage these interconnects are hard to affect.
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I meant to check the signal of the clutch switch. You should also check if the pedals are clearing each switch properly, and sitting correctly when pedals are not depressed. Might have to do some bending of pedal box location. One other thing that cause's the symptoms you have is the steering wheel sensor. That can be disturbed if the steering wheel is out of synch with the sensor, by removal/refitting of the wheel, or tracking that is well out. You can check that in multiecuscan, and adjust it so its centred. Logically, thats unlikely to be your issue, but you don't find much logic when looking for an issue like this on an Alfa.
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Doubt it's anything to do with pedal switches if it appears at ignition on. Usually requires the pedals to be operated before switch errors appear. Also seem to remember that this "Brake Switch" error is a red herring by Alfa that appears for faults unrelated to the switch itself and in fact a true switch fault produces no errors ... just to confuse things. Doesn't this sound like another dodgy fuse connection on the Battery positive fuse plate, one of the big Midi fuses disturbed when the battery was removed, or is that always accompanied by an Immobilizer fault ?
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Aren't twin brake switches usually a NO (normally open) and NC (normally closed) pair ... so the error could easily be apparent if they agree at any point?
The NO is usually linked to the brake-light circuit - and the NC to the cruise control where fitted.
Errors will (should) disable the functioning of cruise control along with probably throwing an error to the ECU
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Thanks all of you for your helpful responses, much appreciated.

Quote:
Originally Posted by addo View Post
I'm wondering if the culprit is in fact the brake pressure sensor.

I believe D97A is up behind the dash, on the right - not in the engine bay. I think it's labelled on the top of itself "3+3+3" and this is D97 A/B/C in essence. My experience has been that save for physical damage these interconnects are hard to affect.
Hi Addo, I've been wondering that too, if it is how do you reset it or get to it?
If the D97A (with B and C) connector is inside the cab it's unlikely to have been snapped, banged or decoupled by my clumsy thrashing around with the gearbox on the other side of the firewall so I'm happy to rule it out at the moment.

Alexie I tend to agree, I didn't disturb anything in the cab at all and the clutch switch shows no fault in mECUscan.

Hugh , thanks for clearing that up but no driving or even using of the pedals took place between it working and not working only a change of the clutch with all that entails electrically, removal of battery, tray and junction box, disconnection of reversing light switch, gearchange cables and slave cylinder, maf and vacuum tubes with the airbox and gearbox battery earth.

Proinsias, yes they are and I think you would be right but the fault occurs without touching either pedal or if you do it makes no difference, and they were working fine till the gearbox came out so I'm tending towards the "not actually the pedal switches theory for the time being

I think the switch thing is either a spurious result caused by a fault in the signal route wiring that I have damaged whilst manhandling the gearbox by myself laid under the car into or out of the clutch/flywheel or it's a different switch like a pressure switch (even though I can't find mention of one in eLearn) As Addo suggests.
( I've made a really long lead for my multitest gauge so I can check the continuity between Pin 16 on the blue connector at the fusebox and Pin 32 on the ABS control connector which is the crucial wiring section, before that point I think it would affect the brake lights as well and at the moment they work perfectly)
if anyone knows something about the/a brake pressure sensor/switch ie, function, location etc please let me know.

Last edited by Yorkshirekeith; 19-10-16 at 18:02.
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The pressure switch is on the back of the ABS bloc. Most of them are a pressure threshold trigger, with a damping mechanism inbuilt. It's possible this one is more sophisticated. Check your grounding, a shameful mistake I made recently involved overlooking a loose ground eyelet.
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OK thanks Addo I'll look at it.
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well it's fixed!
I had two concurrent problems, both causing the same single error, a broken wire in the section of wiring I suspected, thank goodness right next to the ABS control connector where a cable tie holds all the wires together and focuses all the bending. I found that and fixed it with a soldered and heat shrink covered section of exactly 2 cm. that was a eureka moment but then mega-disappointingly that didn't fix it straight away. After recovering from the disappointment of finding out I wasn't as clever as I thought I was I went through all the fuses because I knew the designated ABS ones were all good. it turned out the cruise control fuse was dead. and I'd misread the fuses earlier thinking the Reversing light shared a fuse with the ABS but no it shares it with Cruise control. I'd checked it earlier in the process when checking the reversing light out but must have blown it either when I put the bulb back in and tried it again or during my inept investigations into the ABS failure.
Anyway the dashboard illuminations have reduced to manageable levels again. - occasional Airbag -
Proinsias you were on to it with the cruise control section of the switch but the actual switches weren't to blame, the reversing light socket was very corroded and the bulb had gone, I'd checked the fuse ( I think ) checked the bulb and found that ok as well, put it back in and not really been surprised when it didn't work given the state of the corrosion but Stupidly hadn't rechecked the fuse, thinking that if it wasn't blown before why would it be now? It had, and the F35 fuse is shared with the cruise control, which affects the NO part of the signal from the brake pedal switches to the body computer and gives the brake light switch error.
It misleadingly comes up as a brakelight switch error, on Multiecuscan but if you check the parameters the "brakelight switch" is responding though the "Brake switch" parameter below it isn't.
Anyway I want to thank you all for your suggestions and help.

Last edited by Yorkshirekeith; 21-10-16 at 17:29.
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You would probably also have found that some of the dash illumination around the A/C controls probably wasn't working either. Controls some a weird combination of things F35 which can make it confusing working out what's wrong. Also pretty dumb that a short in the relatively unimportant reversing light takes out the entire ABS, not the smartest bit of design by Alfa.
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Not trying to be picky, but does it actually shut down all aspects of the ABS? Or does it revert to a backup table of values to determine responses?

On the PSA built cars with problematic pressure switches, an ESP failure didn't stop the ABS operation but obviously limited its effectiveness.
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Not trying to be picky, but does it actually shut down all aspects of the ABS? Or does it revert to a backup table of values to determine responses?

On the PSA built cars with problematic pressure switches, an ESP failure didn't stop the ABS operation but obviously limited its effectiveness.
Well it doesn't shut down the module which still responds to MultiECUscan and most of the actuators still worked though- I couldn't tell you which ones from memory- Watching the parameters live, most of them were responding as well, brake pressure for one, but what the ABS would have done in an emergency stop situation is anyone's guess, likely nothing if it's reporting as failed on the dash
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