W212 bonnet open warning

[JohnnyBoy1]

I have a W212 2015 facelift E Class.

It has had a little bump which resulted in needing a new bumper, wing and bonnet.

I have had the car fixed, but however the open bonnet warning sign is still there even though it fully closed.
I replaced the latch sensors on both sides even though the passenger side was untouched, but still showing as bonnet is open. The actual latch works perfectly fine.
Took a quick look at the wiring and connectors they look fine.

I don't know what else I can do in order for the bonnet warning sign to go away.
Hoping somebody has another solution.

 

[John Laidlaw]

That will need a Star reset, you can’t do it yourself unfortunately- Mercedes independent will be a able to sort for you

 

[LostKiwi]

I'd take it back to whoever fixed and get them to sort it.

 

[JohnnyBoy1]

That will need a Star reset, you can’t do it yourself unfortunately- Mercedes independent will be a able to sort for you

Thank you very much, I will have to get Star connected to it unfortunately. Can't fix nothing on these cars without Star I guess.

 

[Uncle Benz]

They are common for the bonnet loops not actually touching the switches enough to operate them. Its a tweak required if that’s the case. Does the warning go away if you give the bonnet a big hard slam shut?

 

[JohnnyBoy1]

They are common for the bonnet loops not actually touching the switches enough to operate them. Its a tweak required if that’s the case. Does the warning go away if you give the bonnet a big hard slam shut?

I've done all sorts with the bonnet, my mechanic has adjusted the bonnet several times but no luck.

 

[JohnnyBoy1]

Star connected to car today, nothing it could do to turn off or reset the open bonnet warning.

I really don't know what else there is I could do tbh.
Wiring/connectors are fine, new sensors fitted and bonnet is perfectly shut, but it is somehow still seeing the bonnet open ‍

 

[Uncle Benz]

I’d suggest working on each switch in turn. Unplug the switch and bridge the plug with a bit ot wire or a split pin and try again. You’ll identify which switch is causing the problem, or prove that the switches are not the problem and it’s elsewhere in the wiring.

 

[JohnnyBoy1]

Managed to sort it.
I think the new sensor needed resetting manually and I did this by:

Popped the bonnet open and held the bonnet lever open from inside and got somebody from the outside to keep on pushing the bonnet in to try and close it. Slammed the bonnet a few times and finally let go of the inside lever and slam the bonnet shut so it locks in.

No open bonnet warning sign since (hopefully it stays this way), I opened the bonnet again, closed it normally and there is no more warning sign.

Hope this helps somebody out in the future, as it was an absolute ball ache driving with that sign on.

 

[oliveau]

I had an instance of the dash warning saying that the bonnet was open when it wasn't. Had a 'phone chat with Col at MBS as I've been stuck in France since 9 March - until today the car hasn't left the garage since then. In the end I took the bonnet latches out and the casings were covered in thick oily dirt where the latches had been lubed previously. So I cleaned all the gunge off with white spirit, split the electric connection plugs and gave them a good squirt of WD 40.put the latches back and drowned them in WD 40 as well. Perfect!

 

[malcolm E53 AMG]

Mines the same a bit temperamental a good slam usually does the job

 

[Ibbig95]

Managed to sort it.
I think the new sensor needed resetting manually and I did this by:

Popped the bonnet open and held the bonnet lever open from inside and got somebody from the outside to keep on pushing the bonnet in to try and close it. Slammed the bonnet a few times and finally let go of the inside lever and slam the bonnet shut so it locks in.

No open bonnet warning sign since (hopefully it stays this way), I opened the bonnet again, closed it normally and there is no more warning sign.

Hope this helps somebody out in the future, as it was an absolute ball ache driving with that sign on.

Im having this exact same issue on my W212 Eclass. It was in a minor front accident, nothing bent or majorly wrong.

Changed the engine, drives perfect but RED hood open warning is driving me crazy! I have bought 2 new hood sensors but it still says it is open. I have adjusted the latches, slammed the hood down. Nothing works, i tried what you did here aswell. Any help?

 

[gg22]

Managed to sort it.
I think the new sensor needed resetting manually and I did this by:

Popped the bonnet open and held the bonnet lever open from inside and got somebody from the outside to keep on pushing the bonnet in to try and close it. Slammed the bonnet a few times and finally let go of the inside lever and slam the bonnet shut so it locks in.

No open bonnet warning sign since (hopefully it stays this way), I opened the bonnet again, closed it normally and there is no more warning sign.

Hope this helps somebody out in the future, as it was an absolute ball ache driving with that sign on.

Hi buddy, I just registered so, that I can thank you. Above worked for me!
I had no fault codes in Xentry but uppon moving the car from parked position the warning of open bonnet would show in the dashboard along with annoying sound alert. The sound alert would eventually stop but the open bonnet picture would always stay in the dashboard no matter what you do.
This created another problem - the wipers would not work when the car is stationary, you have to move for them to start working.
This is now all sorted, thanks very much for sharing!

 

[gg22]

celebration was premature.. it started doing it again.. I think I will take the sensors out, clean them and all that as has been suggested here by oliveau and try again.. let's see

 

[gg22]

Decided to take both hood sensors out and clean them today and discovered the following:
-part number A2128210251 is the right hand sensor, it connect via only 2 wires and there is no mechanical switch in it, it senses if the hood is closed electromagnetically.
-part number A2128210151 is the left hand sensor, it connects via 4 wires and in addition to the electromagnetic part it has a mechanical type of switch.
There is a piece of thin metal strip on top of it which presses on the switch below when the hood is closed.
Don't know why Mercedes decided to have both mechanical and electromagnetic sensing for this one.
Mine was broken, the metal strip was dislodged and messed up.
If you disconnect either of these you will get open circuit fault code if you have a way to read the OBD codes.
If you disconnect the left one you will also get "Active bonnet" message on the dashboard.
The new sensor (A2128210151) should be arriving soon and will update here with the results.

 

[Blobcat]

Decided to take both hood sensors out and clean them today and discovered the following:
-part number A2128210251 is the right hand sensor, it connect via only 2 wires and there is no mechanical switch in it, it senses if the hood is closed electromagnetically.
-part number A2128210151 is the left hand sensor, it connects via 4 wires and in addition to the electromagnetic part it has a mechanical type of switch.
There is a piece of thin metal strip on top of it which presses on the switch below when the hood is closed.
Don't know why Mercedes decided to have both mechanical and electromagnetic sensing for this one.
Mine was broken, the metal strip was dislodged and messed up.
If you disconnect either of these you will get open circuit fault code if you have a way to read the OBD codes.
If you disconnect the left one you will also get "Active bonnet" message on the dashboard.
The new sensor (A2128210151) should be arriving soon and will update here with the results.

Pictures always good and welcome

 

[gg22]

Blobcat, here the two sensor from photos I found on the internet.

 

[gg22]

And couple of more tips how to disconnect the cable connector and slide the sensor out.
It took me some time to figure it out so I am sure it will be helpful for people that do it for the first time.

 

[gg22]

Today I received the new sensor and fitted it.
The open bonnet message is gone!!!
Attaching side by side photo of old (broken) and new sensors.

 

[tripper262]

Hi all,

I've got a similar problem on my E class. Are there any obvious things to try since its getting really annoying

I've taken the latch out couldn't really see how the microswitch is getting moved by the mechanics of the latch. The cars a 2015 E Class estate. I'm getting various waring from the collision avoidance system too - although I believe this to be non-related.

Anyone know if there switches on both sides ? . Even if I could trigger the switch either side that would let me know if the switch needs replacing - and which point I'd probably take this to a garage..

Any pointers appreciated