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matgriff

Active Member
I noticed on my 53 reg Disco 2 that the bonnet switch that's mounted on the nearside inner wing, about 3/4 of the way down is tie wrapped in the down (bonnet closed) state...

Does this switch operate a light or something under the bonnet ? I couldn't see one, or is it just part of the alarm/immobiliser system ?

Maybe the switch is dodgy, but my Hawkeye reports it as "bonnet closed"

Are these usually troublesome ? If so I'll just get a new one.

Thx
 
The switch does two things, gives an indication (mislock double beep) of the bonnet being unlocked on locking the vehicle/setting the alarm, also activates the alarm if the bonnet is opened with the alarm set.
Its not unknown for the switch to have issues and give false alarms, if so just replace if faulty. Simples.
 
OK thanks. I'll just replace it as obviously a previous owner has felt the need to tie wrap it down at some time.
 
That's silly cos the switch is N/C so to make trouble it must be stuck closed which means like when the bonnet is open, if it gives misslock warning with closed bonnet the simplest way is to unplug it, to tie wrap it down makes no sense, maybe it was just missaligned and didnt open when the bonnet was closed so better untie it and try, if it gives misslock bond a piece of rubber on the bonnet above it as to increase the plunger's travel and IMO it will be OK
 
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If the switch is N/O (normally open) as you state.... that means in the resting state, ie when the bonnet is open, the switch contacts are also open. When you press the switch, ie close the bonnet the switch closes and makes the circuit.. so tie wrapping it down would simulate having the bonnet permanently closed.

It's most likely not the switch itself, if it was the switch just tie wrapping it closed would still give a problem. most likely it's not being pressed correctly by the bonnet, as you say, but a new switch is £6 so I'll get that and then fix it. It could be that the switch contacts are corroded, so it needs to be tightly pushed to make..
 
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Sorry i had a mental hiccup, the switch is N/C so closes to earth in released position aka when the bonnet is opened so tie wrapping it down is open like when it's not there, non-sens to do that , (i edited my previous message too)
 
On the subject of bonnet switches, I've found that if I unlock the car to do something under bonnet and then close it, I'll get a short blat of the horn when I re-lock it on the fob. The LED on the dash also flashes very quickly.
If I then open the car again and turn the ignition on, then shut and re-lock the car, it's happy. it seems that I can't open the bonnet without it thinking it's still open when I re-lock it.

Is this is a fault or a 'feature'? The car is a '52 plate, I don't remember my old X reg doing it though.
 
It's not a fault nor a feature it's a common glitch cos the bonnet switch is on a different circuit than the door switches and has to open the earth path of a live circuit as to rise voltage from below 2V to above 6V which at first attempt can have certain a delay... the door switches are on a open earth path so different.... wait few seconds after you closed the bonnet before you lock and you'll see it will not do that thing
Input/Output
When the bonnet is closed the bonnet activated alarm switch is in an open condition and the input to the BCU is more
than 6 volts, in which case the BCU pulls the input high internally. When the bonnet is open the bonnet activated alarm
switch is closed and the input to the BCU is less than 2 volts.
The bonnet activated alarm switch has a dedicated signal input to the BCU. This allows the BCU to identify the
position of the bonnet.
 
Ah, OK - thanks. I'll try waiting a bit next time and see what happens.
 
Yes, mine's the same - have to wait a few seconds after closing the bonnet before locking otherwise get a mislock sound.
 
What does this switch look like on your cars?

1) I can't find what you mean

2) If I do find it, how do I know if it's buggered visually?
 
It's simple if you search where you should which means the workshop manual... i hope that what you see as nr 6 in the attachment is clear enough... if it's not there but unplugged and the plug hanging around it has no effect other than the alarm will not go off when the bonnet is opened with locked vehicle nothing else, once unplugged it's like the bonnet is closed all the time cos it's a N/O switch to earth and the alarm or misslock warning comes on when the switch closes to earth when the bonnet is opened so as long is open circuit there no misslock if you see what i mean

1720963317537.png
 
MAF Diver said:
Yep, gotcha! I thought it was that. Mine looks a bit sad, the top of it is hanging down/bent.

I'm having some SLS/airbag dropping issues and I wonder if this is the culprit!
Click to expand...
The bonnet switch has absolutely nothing to do with SLS...only with the alarm/misslock, if you have misslock warning unplug it and if nothing changes it's not the switch
 
sierrafery said:
The bonnet switch has absolutely nothing to do with SLS...only with the alarm/misslock, if you have misslock warning unplug it and if nothing changes it's not the switch
Click to expand...
This guy on the forum said that he was having SLS/airbag issues and it was due to a problem with one of his doors:

HI had a similar problem with mine changed most things even the filter nsr behind the lamp unit , rebuilt the compressor etc then when I was going through nano com I saw that drivers door lock had intermittent fault checked wiring and changed the lock assy been ok since
Click to expand...
 
MAF Diver said:
This guy on the forum said that he was having SLS/airbag issues and it was due to a problem with one of his doors:
Click to expand...
An open door input disables the compressor only so if it's that it will not kick in when necessary that's all ...if it's about some weird SLS behaviour other than complete lack of inflation it has nothing to do with door swicthes unless it' a very intermittent switch input
 
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sierrafery said:
An open door input disables the compressor only so if it's that it will not kick in when necessary that's all ...if it's about some weird SLS behaviour other than complete lack of inflation it has nothing to do with door swicthes
Click to expand...
Copy. Does air escape from non-faulty airbags when driving/hitting bumps, etc.?
 
If the dampers are soft and the vehicle's speed is below the ACE activity limit it's possible that when a bump is hitted the movement of the body up or down to be higher than the the sensor's target height margins and the SLABS ECU will try to adjust the level accordingly with tye exhaust valve or compressor
 
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Interesting!

Yep, the front and rear shocks are really soft (they need to go!)

I had both bags completely deflate happen at quite some speed recently though (around 40mph), but went over corrugations and some bumps in the road.

Another time it happened at city speeds 20-25mph but with a bunch of speed bumps in a row
 
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