2015 V40 (D4) - Dreaded 'Bonnet Open' Message
 

Hi,



I have recently had a constant warning appear on the dash indicating that the bonnet is open but is very much firmly closed and locked. (the usual graphic of the car but showing the bonnet in white indicating it is open)



Having had a search around on the forum, others have had the same issue but no one seems to have found the exact cause of this or a proper fix other than spraying copious amounts of WD40 into the catch mechanism which sometimes works (didn't for me) and sometimes this is only a temp fix.



Has anyone experienced this and found out a good way of curing the problem without the need of a dealer visit?



I've also noticed that whilst the car thinks the bonnet is open, it disables the start/stop functionality which is irritating.



Thanks in advance!

bumpety bump

Bonnet open message cure
 

Hi we had the same problem and cured it. Based on a 2014 D4.
The left hand catch has the micro switch.
Basically the two catches are mechanical affairs and passenger side one has a micro switch as well. This fix took about 15 mins.
It was lubricating the catches that caused the problem, as the lubricant got into the micro switch and prevented it making contact, hence it registered bonnet open.
This is what we did.

Temporary cure,
Remove the passenger side headlamp, one x tor’x screw, lift out the bonnet bump stop, (I love the way Volvo thought to make this removable), then you can pull and rotate the headlamp out and remove the wiring plug.
You will see that the wire from the hinge has a connector to the wiring loom at the side of the headlamp. It is actually at the wrong side of a panel for you but the plastic lugs stick thorough and can be squeezed with pliers and pushed towards the centre of the car.
You should be able now to separate the connector. The pins are on the catch side, the sockets on the loom side which is good.
Short out the two sockets on the loom so it forms a continuous loop, (this is all the switch does, it connects these two wire together), I used a small electrical spade connector and bent it to fit. Your bonnet open light should now be off (permanently).
Cover the loom connector with tape and cable tie the wire so it doesn’t glob about.

Permanent fix.
Look into the passenger side hinge with a torch from the top. You should be able to see the micro switch as it has a tiny red button on it, deep down, on the headlamp side.
Spray the micro switch with electrical contact cleaner, or brake and clutch cleaner, but nothing oily.
Toggle the micro switch button on and off numerous times to get the cleaner through it.
I used a small hex key as it was the right size to press the little red button.
Now leave it all to dry, for several weeks and repeat as needed!!
You can test if the micoswitch is working by putting an electric meter set to resistance across the pins and toggling the switch, you should see it change. Alternatively just plug it back together and see if it works.
When it is working again, remove the headlamp and clip the connectors back into the panel.
If it never works you can get used catches from eBay, or new micro switches from electronics retailers, but it looks to be a pain removing the whole lock mechanism which is tucked behind the bumper.

Our problem occurred after lubricating the locks, it took 3 weeks for the micro switch to dry out properly, it has been fault free for months now.
It taught me to be very careful where I lubricate the catches and not to spray liberally.

Good luck and let us know how you get on.

Hi binty,

Thanks so much for the detailed reply - I am attempting this now.

I've got the headlight off; where you mention the bump stop, is that the structure which is running right across both sides of the engine bar just behind the bumper?

Thanks,
Seb

Ok, so I have managed to get both the headlights off and have found the connector on the drivers side so about to connect that to create the continuous loop.

Question, I cannot for the life of me locate the micro switch with the red button on the passengers side; is it accessible without dismantling more of the car or should I be able to see it with just the headlight removed?

Thanks,
Seb

Micro switch and bump stop
 

Hi
The bump stop is the round rubber thing that supports the bonnet at the side of the headlamp torx screw. it just lifts out.
The micro switch you can see without removing anything.
When stood at the front of the car look down inyo the passenger side catch and to the right.
I am going to try and get you a photo.

Thank you.

I tried to short the circuit using a simpler wire however this didn't work and it is still telling me the bonnet is open when indeed it is shut. I think I will need to get a better bridge between the two connections, such as the spade connector you used.

Ok, so onto the red button in the deep of the hinge on the lamp side.

I haven't been able to locate this for love nor money - here are some photos of the hinge I am looking at whilst trying to stare down it.

photos
 

Hi,
I just nipped out and tried it, noting exactly what I did, so here goes.
Unfortunately I can't get a good photo inside the catch so hope this helps.
The switch is underneath the round spring, towards the front of the car. You can jus see it if you get the right light and angle, but it is easier to feel as described below.

Insert a thin hex key into the catch and hook under the round spring.
Keep the shaft of it touching the spring.
Gently rotate the hex key clockwise until it stops against the inside of the catch.
Lower it down keeping gentle rotation pressure on and you will feel the tip of the key twist into the gap between the catch mechanism and the microswitch.
You should now be able to press the microswitch down, it is only a couple of mm, and it should click softly. You can toggle it on and off with the hex key and it will click each time.
It is more like watchmaking than car mechanics.
I attach some photos, including one showing what angle the hex key is at when it contacts the microswitch.
Also one of the bump stop.

Good luck and I can understand why it may be difficult to make the loop with wire, the terminals are for flat pins I recall, and quite deep inside the plug. I attach a photo of the bridge i made from a forked electrical terminal, twisting the forks 90 degrees so they are parallel.

Pictures of microswitch
 

I just remembered I have one of those small fibre optic cameras so here are pictures of the microswitch which is in orange.
First one shows position relevant to the round spring taken from above the catch, second is a close up

Thanks very much Binty.

So, an update. I didn't end up with a huge amount of successful however I did eventually manage to locate the micro switch - notably the clicking sound gave it away. Your comparison to watchmaking is near on perfect; this is a very tricky job to do. So, having depressed the switch several times and used some contact cleaner; I am in no better position so I suspect that the switch has lived its final days and a new one is in order.

Having had a quick look online for the catches, they look a bit of a pain to fit (bumper off job) as it comes complete with the connecting wire for the catch on the drivers side which runs under the bumper top edge.

Thanks again for all your help - they were invaluable :regular_smile: