W212 'Active bonnet' nuisance feature work around

[Not_Anumber]

Last week a fox ran out in front of my S212 as I was driving round an uphill bend on a heavily potholed road. I braked mildly but then all hell broke loose as the car decided to activate both the active braking and the active bonnet features, the latter leaving me confused, bemused and most definitely not amused.

There were no warning lights or messages but the rear of the bonnet was now 2 to 3 inches higher. The front was still at its normal height and the bonnet catch was still in place. Given that bonnet hinges at the back and opens from the front normally it was clear that something quite odd had happened for it to be so out of line at the windscreen end. There was no mark on the front of the car and indeed the fox lived on unscathed to chase rabbits and raid bin and hopefully to avoid illicit huntsmen for the rest of it's days.

I started to look on this and other forums, read the section in the owners manual, yawned my way through several mostly pointless youtube videos and was frankly surprised how little proper, useful information is out there. Several articles just said what a good feature it is clearly without the authors knowing the first thing about it, a couple that reprinted the not very well written section an the active bonnet from the owners manual which made even less sense without any diagrams. Several slightly better articles about how to cope with clearing warning messages, which I didn't have. Some vague and limp comments about having to take it to a main dealer for either a 'reset' or replacement of the actuators - a process the authors clearly didnt know about and wildly different ideas of cost.

So heres the information that doesn't seem to be out there. I hope this plugs a useful knowledge gap for some and helps a few people to fix their cars themselves and save themselves being ripped off.

The idea of the Active Bonnet feature is to give pedestrians a slightly softer contact area in a collision at mainly urban traffic speeds. The car will react to a hit on the front bumper by letting off the actuators the bonnet hinges are mounted to. Being spring loaded they instantly raise the back of the bonnet, changing the angle and creating a bit more space between the surface of the bonnet and the top of the engine, but only at the back. . It's of fairly limited usefulness, is disabled at higher speeds and is optional, not fitted to all W212s. It is not obligatory to have this feature and it is not checked at the MOT.

Some articles wrongly state that the actuators are pyrotechnic, like airbags. They arent or at least they arent on mine. These actuators contain a powerful electromagnet which release a catch allowing the top of the unit to shoot upwards taking the hinges and bonnet with it.

Ive no idea what the actuators would cost new from Mercedes as I hadnt the slightest wish to buy new. Check with your local main dealer if you want to go the new part route but save the money on labour and fit them yourself. I bought 2nd hand units from a breaker on Ebay who had lots of positive reviews. I got the pair for £ 70, delivered.

With 2 people to help I undid the 2x horitontal 13mm bolts each side that hold the hinges to the top of the actuators and then lifted the bonnet clear. Its best here to use a marker of some sort first to draw round the position of the bolts on the hinges. It saves having to bugger around adjusting it all later to get the bonnet to fit just right. Yep, i didnt think of this until later.

I opted to disconnect the car battery just in case the actuators were pyrotechnic (given the conflicting information on the internet) but also because i wanted to reduce the chances of it throwing a warning light or code that might need to be cleared by a specialist. This may have been unnecessary but 30 seconds disconnecting the battery negative terminal with a 10 mm spanner and 30 minute wait for the SRS system to discharge seemed like a good idea at the time.

I removed the two 13mm nuts holding each actuator in place. I used a narrow marker to draw round the actuator before undoing it so I could be sure to put the replacement back in exactly the same place, . Each actuator has a simple a 2 wire electrical connection that needs separating. Connect the replacement actuator, lower it in and do up the 2 nuts. Do this for both sides.

Bring the bonnet back to the car and bolt the hinges to the top of the actuators. If you marked the hinges it will make it more likely the bonnet will be perfectly aligned first time.
--

Right, and now for the bombshell - well ok not quite but it might surprise the odd person. (yeah ok If this does surprise you please dont think I am calling you odd).

There is a work around where you can instead just bin the actuators and not replace them. The feature can be deleted.

Remember I mentioned that not all W212's had the feature. You can choose to remove the actuators and instead attach the hinges to the body directly in the traditional manner. This does not need any modification, it doesnt need you to buy different hinges, bolts or special brackets as you already have all the necessary hardware there on the car. Take another look at the base plates on the inner wing, the surrounds that the actuators are fitted into. Look for the vertical section and you will see a plastic cover a couple of inches long. It prises off easily with a screwdriver revealing 2 threaded holes. Now if you look at the bonnet hinges you will see a 2nd set of mounting holes. They will be closer together than the ones that are used if bolting to the actuators. Now line these up with the holes you uncovered on the vertical section of the baseplate and bolt them together with the 13mm bolts you have in your hand. Adjust bolt position to suit bonnet alignment. The bonnet is now fitted in the traditional way directly to the body and the actuators can go out with the recycling.

I have measured the resistance across the actuators as roundabout 1.6 Ohms. If you want to be cautious you could put suitable value resistors across the connectors both sides. It will avoid any warnings just in case there is an ECU in the car that is checking there is resistance present.

There you are. Despite the paucity of information Ive proved this can be done on a W212 at a sensible cost with 2nd hand actuators and there is the very useful option of deleting the actuators and just having normal hinges.

If another fox jumps out I will certainly be going for the delete next time

 

[AMGeed]

Thanks for taking the time to record your fix and workaround to delete the actuators.

 

[SL63 Mark]

Yes, I would delete them, sounds like a useless feature.

 

[Snake Charmer]

Great writeup. Did you perform a post mortem on the old units to see if they are one shot items or resettable?

 

[Not_Anumber]

I did take one apart out of curiosity today.
The actuator has a surprisingly elaborate mechanism with 3 independently moving sprung loaded sections, consisting of pillars at each end each with their own springs plus a larger central section that has 2 really powerful springs. It took some while to spot how the latch mechanism works. It isnt very obvious as there are 2 moveable rods built into the 'lid' that engage with indentations in the main body section's outer casing. When the solenoid is energised it must move these latches and the actuator then springs open like a jack in the box.
I had it clamped in a vice and even with the 2x more powerful central springs removed I wasnt able to exert enough force in any controllable way to get the lid latching back into place at both ends . It may work given enough force and possibly there may be a need to blip the solenoid just at the right moment during reassembly but I cant be certain.
It may in theory be re-settable but would need a powerful press just to try it. The jury has to stay out on that one Im afraid until someone else can confrm.

 

[malcolm E53 AMG]

Thanks for posting this - pics would be nice as I have the same car and haven’t a clue whether I have the actuators or not or a build code would clarify

 

[ajlsl600]

Last week a fox ran out in front of my S212 as I was driving round an uphill bend on a heavily potholed road. I braked mildly but then all hell broke loose as the car decided to activate both the active braking and the active bonnet features, the latter leaving me confused, bemused and most definitely not amused.

There were no warning lights or messages but the rear of the bonnet was now 2 to 3 inches higher. The front was still at its normal height and the bonnet catch was still in place. Given that bonnet hinges at the back and opens from the front normally it was clear that something quite odd had happened for it to be so out of line at the windscreen end. There was no mark on the front of the car and indeed the fox lived on unscathed to chase rabbits and raid bin and hopefully to avoid illicit huntsmen for the rest of it's days.

I started to look on this and other forums, read the section in the owners manual, yawned my way through several mostly pointless youtube videos and was frankly surprised how little proper, useful information is out there. Several articles just said what a good feature it is clearly without the authors knowing the first thing about it, a couple that reprinted the not very well written section an the active bonnet from the owners manual which made even less sense without any diagrams. Several slightly better articles about how to cope with clearing warning messages, which I didn't have. Some vague and limp comments about having to take it to a main dealer for either a 'reset' or replacement of the actuators - a process the authors clearly didnt know about and wildly different ideas of cost.

So heres the information that doesn't seem to be out there. I hope this plugs a useful knowledge gap for some and helps a few people to fix their cars themselves and save themselves being ripped off.

The idea of the Active Bonnet feature is to give pedestrians a slightly softer contact area in a collision at mainly urban traffic speeds. The car will react to a hit on the front bumper by letting off the actuators the bonnet hinges are mounted to. Being spring loaded they instantly raise the back of the bonnet, changing the angle and creating a bit more space between the surface of the bonnet and the top of the engine, but only at the back. . It's of fairly limited usefulness, is disabled at higher speeds and is optional, not fitted to all W212s. It is not obligatory to have this feature and it is not checked at the MOT.

Some articles wrongly state that the actuators are pyrotechnic, like airbags. They arent or at least they arent on mine. These actuators contain a powerful electromagnet which release a catch allowing the top of the unit to shoot upwards taking the hinges and bonnet with it.

Ive no idea what the actuators would cost new from Mercedes as I hadnt the slightest wish to buy new. Check with your local main dealer if you want to go the new part route but save the money on labour and fit them yourself. I bought 2nd hand units from a breaker on Ebay who had lots of positive reviews. I got the pair for £ 70, delivered.

With 2 people to help I undid the 2x horitontal 13mm bolts each side that hold the hinges to the top of the actuators and then lifted the bonnet clear. Its best here to use a marker of some sort first to draw round the position of the bolts on the hinges. It saves having to bugger around adjusting it all later to get the bonnet to fit just right. Yep, i didnt think of this until later.

I opted to disconnect the car battery just in case the actuators were pyrotechnic (given the conflicting information on the internet) but also because i wanted to reduce the chances of it throwing a warning light or code that might need to be cleared by a specialist. This may have been unnecessary but 30 seconds disconnecting the battery negative terminal with a 10 mm spanner and 30 minute wait for the SRS system to discharge seemed like a good idea at the time.

I removed the two 13mm nuts holding each actuator in place. I used a narrow marker to draw round the actuator before undoing it so I could be sure to put the replacement back in exactly the same place, . Each actuator has a simple a 2 wire electrical connection that needs separating. Connect the replacement actuator, lower it in and do up the 2 nuts. Do this for both sides.

Bring the bonnet back to the car and bolt the hinges to the top of the actuators. If you marked the hinges it will make it more likely the bonnet will be perfectly aligned first time.
--

Right, and now for the bombshell - well ok not quite but it might surprise the odd person. (yeah ok If this does surprise you please dont think I am calling you odd).

There is a work around where you can instead just bin the actuators and not replace them. The feature can be deleted.

Remember I mentioned that not all W212's had the feature. You can choose to remove the actuators and instead attach the hinges to the body directly in the traditional manner. This does not need any modification, it doesnt need you to buy different hinges, bolts or special brackets as you already have all the necessary hardware there on the car. Take another look at the base plates on the inner wing, the surrounds that the actuators are fitted into. Look for the vertical section and you will see a plastic cover a couple of inches long. It prises off easily with a screwdriver revealing 2 threaded holes. Now if you look at the bonnet hinges you will see a 2nd set of mounting holes. They will be closer together than the ones that are used if bolting to the actuators. Now line these up with the holes you uncovered on the vertical section of the baseplate and bolt them together with the 13mm bolts you have in your hand. Adjust bolt position to suit bonnet alignment. The bonnet is now fitted in the traditional way directly to the body and the actuators can go out with the recycling.

I have measured the resistance across the actuators as roundabout 1.6 Ohms. If you want to be cautious you could put suitable value resistors across the connectors both sides. It will avoid any warnings just in case there is an ECU in the car that is checking there is resistance present.

There you are. Despite the paucity of information Ive proved this can be done on a W212 at a sensible cost with 2nd hand actuators and there is the very useful option of deleting the actuators and just having normal hinges.

If another fox jumps out I will certainly be going for the delete next time

Grand write up. I will be looking to dump that "facility" any time that issue crops up. If it was spring loaded and re settable without going near the dealers, breakers I wud keep it. But as designed, nah! In the bin.

 

[ajlsl600]

anyway I had a good deflector on car for 30 Yr. Its called a bull bar. Never gave me any issues!!!!!!

 

[anyweb]

Last week a fox ran out in front of my S212 as I was driving round an uphill bend on a heavily potholed road. I braked mildly but then all hell broke loose as the car decided to activate both the active braking and the active bonnet features, the latter leaving me confused, bemused and most definitely not amused.

There were no warning lights or messages but the rear of the bonnet was now 2 to 3 inches higher. The front was still at its normal height and the bonnet catch was still in place. Given that bonnet hinges at the back and opens from the front normally it was clear that something quite odd had happened for it to be so out of line at the windscreen end. There was no mark on the front of the car and indeed the fox lived on unscathed to chase rabbits and raid bin and hopefully to avoid illicit huntsmen for the rest of it's days.

I started to look on this and other forums, read the section in the owners manual, yawned my way through several mostly pointless youtube videos and was frankly surprised how little proper, useful information is out there. Several articles just said what a good feature it is clearly without the authors knowing the first thing about it, a couple that reprinted the not very well written section an the active bonnet from the owners manual which made even less sense without any diagrams. Several slightly better articles about how to cope with clearing warning messages, which I didn't have. Some vague and limp comments about having to take it to a main dealer for either a 'reset' or replacement of the actuators - a process the authors clearly didnt know about and wildly different ideas of cost.

So heres the information that doesn't seem to be out there. I hope this plugs a useful knowledge gap for some and helps a few people to fix their cars themselves and save themselves being ripped off.

The idea of the Active Bonnet feature is to give pedestrians a slightly softer contact area in a collision at mainly urban traffic speeds. The car will react to a hit on the front bumper by letting off the actuators the bonnet hinges are mounted to. Being spring loaded they instantly raise the back of the bonnet, changing the angle and creating a bit more space between the surface of the bonnet and the top of the engine, but only at the back. . It's of fairly limited usefulness, is disabled at higher speeds and is optional, not fitted to all W212s. It is not obligatory to have this feature and it is not checked at the MOT.

Some articles wrongly state that the actuators are pyrotechnic, like airbags. They arent or at least they arent on mine. These actuators contain a powerful electromagnet which release a catch allowing the top of the unit to shoot upwards taking the hinges and bonnet with it.

Ive no idea what the actuators would cost new from Mercedes as I hadnt the slightest wish to buy new. Check with your local main dealer if you want to go the new part route but save the money on labour and fit them yourself. I bought 2nd hand units from a breaker on Ebay who had lots of positive reviews. I got the pair for £ 70, delivered.

With 2 people to help I undid the 2x horitontal 13mm bolts each side that hold the hinges to the top of the actuators and then lifted the bonnet clear. Its best here to use a marker of some sort first to draw round the position of the bolts on the hinges. It saves having to bugger around adjusting it all later to get the bonnet to fit just right. Yep, i didnt think of this until later.

I opted to disconnect the car battery just in case the actuators were pyrotechnic (given the conflicting information on the internet) but also because i wanted to reduce the chances of it throwing a warning light or code that might need to be cleared by a specialist. This may have been unnecessary but 30 seconds disconnecting the battery negative terminal with a 10 mm spanner and 30 minute wait for the SRS system to discharge seemed like a good idea at the time.

I removed the two 13mm nuts holding each actuator in place. I used a narrow marker to draw round the actuator before undoing it so I could be sure to put the replacement back in exactly the same place, . Each actuator has a simple a 2 wire electrical connection that needs separating. Connect the replacement actuator, lower it in and do up the 2 nuts. Do this for both sides.

Bring the bonnet back to the car and bolt the hinges to the top of the actuators. If you marked the hinges it will make it more likely the bonnet will be perfectly aligned first time.
--

Right, and now for the bombshell - well ok not quite but it might surprise the odd person. (yeah ok If this does surprise you please dont think I am calling you odd).

There is a work around where you can instead just bin the actuators and not replace them. The feature can be deleted.

Remember I mentioned that not all W212's had the feature. You can choose to remove the actuators and instead attach the hinges to the body directly in the traditional manner. This does not need any modification, it doesnt need you to buy different hinges, bolts or special brackets as you already have all the necessary hardware there on the car. Take another look at the base plates on the inner wing, the surrounds that the actuators are fitted into. Look for the vertical section and you will see a plastic cover a couple of inches long. It prises off easily with a screwdriver revealing 2 threaded holes. Now if you look at the bonnet hinges you will see a 2nd set of mounting holes. They will be closer together than the ones that are used if bolting to the actuators. Now line these up with the holes you uncovered on the vertical section of the baseplate and bolt them together with the 13mm bolts you have in your hand. Adjust bolt position to suit bonnet alignment. The bonnet is now fitted in the traditional way directly to the body and the actuators can go out with the recycling.

I have measured the resistance across the actuators as roundabout 1.6 Ohms. If you want to be cautious you could put suitable value resistors across the connectors both sides. It will avoid any warnings just in case there is an ECU in the car that is checking there is resistance present.

There you are. Despite the paucity of information Ive proved this can be done on a W212 at a sensible cost with 2nd hand actuators and there is the very useful option of deleting the actuators and just having normal hinges.

If another fox jumps out I will certainly be going for the delete next time

great info, and it would have been even better if you could attach some photos of the bits you replaced, but thanks for the info !

 

[Not_Anumber]

great info, and it would have been even better if you could attach some photos of the bits you replaced, but thanks for the info !

You dont need photos. A look under the bonnet of a W212/ s212 will reveal whether or not it has the actuators. If the bottom of the hinges look to be bolted into 2.small cylinders that form part of a lump of a unit which has a part number sticker then you are already staring at the top part of the actuator, the tip of the iceberg so to speak,
. However if the bottom of the hinge is just bolted onto a small upturn made of the same thickness metal as the hinge then the hinge is directly mounted to the body, old school style and you dont have the actuators.

 

[Not_Anumber]

for those who like photos then. Yep you can't really miss this lump of a thing

 

[Not_Anumber]

And this is what a deployed one looks like. You could choose to bolt the hinges straight to the bodywork and lose these lumpy spring loaded monstrosities. I only realised that after buying replacement actuators though.

 

[ajlsl600]

That will be my plan.

 

[FD862]

View attachment 84631
And this is what a deployed one looks like. You could choose to bolt the hinges straight to the bodywork and lose these lumpy spring loaded monstrosities. I only realised that after buying replacement actuators though.

The owners manual of my 2011 E250 states it can be reset by (gently) using bonnet as leverage. No disassembly or replacement required.

 

[Not_Anumber]

Lol Thats printed in my copy of the 212 owners manual too and was the first thing I tried. Have you mentioned this because you have actually managed it successfully ? Ive yet to hear anyone who has managed it in situ.
Opening the bonnet to it's highest position and pulling down against the hinges as directed didnt reset the actuators. But removing the bonnet, holding the actuators in a vice and re compressing them with a large woodworking G clamp worked very well, though a little more time consuming. Mine will be going back on when i can face removing and refitting the bonnet again.

If you do choose to do away with the actuators then to prevent the Active Bonnet warning message you will need to use a 1.6 ohm resistor each sde. This works perfectly The resistors cost penies and just plug into the connectors that were unplugged from the actuators. Cut the legs to length and use some 1mm insulated tubing round the exposed parts of the resitors' legs. If you are making this a permanent work around you should bind the resistor and connector with waterproof self amalgamating tape . (Not required in my case as I only did the work around to prove it could be done )