- My model of MX-5 is: _4th Gen_1.5
- I’m based near: __Ludlow
- I’m looking for technical help or recommendations on: __Active bonnet warning light comes on and flashes on my MX-5 18 plate 1.5 and having taken the car for a service at main dealer, they checked the sensors which seem to be fine but couldn’t locate the problem beyond a ‘circuit short to the battery’. They said it could take 3 hours to check and would cost north of £400 any suggestions on how to avoid paying such amount?
First port of call would be the fault memory.
Did Mazda read those?
As you must have had one if the light came on.
Water ingress in the connectors in the front bumper would be a good guess at this stage.
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Start with a battery disconnect, possibly the ECU has hung up.
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Im no expert, but have you tried bypassing this , and if so does the issue still persist ?? you need a resistor (that the one I used PATIKIL 5W 2.2 Ohm Aluminum Shell Resistor, 2 Pack Aluminum Housing Resistor Housed Case Wirewound Resistors Screw Tap Power Resistor, Golden : Amazon.co.uk: Business, Industry & Science ) or buy someone else “tool” https://www.dsgarage.it/store/en/custom-harnesses/262-mx5-nd-and-fiat-abarth-124-active-bonnet-delete-kit.html might sort your issue, and than you can isolate the faulty pedestrian protection system or what ever its called
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The site for the active bonnet delete kit suggests that it stops “false bonnet activation” That is obviously for track days etc, but it begs the question, have there been false bonnet activations in normal road use? and if there have been, under what circumstances would it happen? ie; could a pot hole for instance set it off? 
My understanding of the active bonnet system is that the 6 front impact sensors signal the specific ECU located behind the rear bulkhead and activate the bonnet rams. Putting a resistor in and by passing the rams will prevent the rams from activating however the system may well think they have been activated as the sensors will have sent a signal to the ECU and the flashing warning light will appear, I do not think this ECU can be reset unless removed from the car and sent to an expert
This active bonnet system is not part of the BCM and cockpit airbag systems. It is an add on system for certain markets. It is not mandatory and it is not part of Construction and Use regulations and is not part of the MOT test requirement.
I think you will find it is.
It is treated as the same as an airbag warning light which is an automatic failure due to it being part of the cars safety systems.
Happy to be proved wrong by all means as been out of the field for a while.
EDIT.
“A Mazda MX-5 pedestrian protection system (active bonnet) warning light being on is a
Major defect and will result in an MOT failure.
The fault is classified under Section 7: Other Equipment, specifically related to the Supplementary Restraint System (SRS) and airbag system fault, as the active bonnet deployment is connected to the vehicle’s safety sensors”.
In other words all linked together as a complete safety system.
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The Active Bonnet System is not part of the Supplementary Restraint System, The SRS is all about air bags and occupant protection. The SRS warning light is not activated if the Active Bonnet System has deployed. It is a separate flashing warning light in the binnacle. The impact sensors for the SRS system are not used for the Active Bonnet which has its own more sensitive sensors. This is why the bonnet deploys for minor impacts and the occupant ones do not.
May I ask where your information has come from?
Because, of the researched information and indeed still believing it is part of the integrated safety systems I have just spoken with my local Mazda Service Manager to double check and get his advice.
He has confirmed it IS part and parcel of the safety SRS system and if that RED light comes on and stays on or continues to flash, then it is an a Major fault and therefore a MOT failure.
Are we talking about the same thing. 
(Sourced from this Forum).
I feel I should clarify that my suggestions its for troubleshooting the issue, and the bypass is recommended for track /trackday use when and accidental ding can trigger the system or I am sure I had read online some reported hard breaking…
I’ve tested both DIY method and the Italian chap tool, my DIY dongle doesnt sit perfectly, so I have low confidence in it on track use, that all I can add for now 
.
Good luck
BMW forums are full of people whose cars have failed MoT due to the struts having an expiry date. The expiry must not be later than the next brake fluid change date.
I’m amazed at that, having had two shock failures in Mac struts in the past (Zephyr, Astra), and still being able to finish the trips - gently gently with the right foot.
But it might explain the two hour traffic jam I was in Friday (27th) morning last week heading NW on the M40 a couple of miles short of Gaydon.
When we passed the “incident” a large black BMW was facing the wrong way in the fast lane with front right wheel and suspension sticking out sideways, and about to be loaded on the recovery truck.
At the time I guessed the lower ball joint had failed when it hit a pot hole (far too many on that very fast road).
But can a modern strut failure have a similar effect?
BMW Active bonnet struts have an expiry date they last about 5 years and it’s checked for MoT. Not the suspension struts.
As for the car you saw it most likely rear ended someone. A good 60mph whack can do that.
Good point, but no other damage was obvious on my five second crawl past. I did not notice if airbags had gone off.
Nor was there any debris or yellow markers or any other vehicles apart from recovery and the three hi-vis police cars. These included the Traffic car I’d been following at a distance along with everyone else at my usual sat-nav-70 since Wycombe.
It’s interesting to watch how drivers improve their behaviour when a marked car is setting a good legal pace with exemplary signalling and lane selection.
Car passed its MOT at Mazda garage even with the Active bonnet system light on.
these are the notes the mechanic added. I’m not technical and it makes no sense to me.
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The ‘B1422’ code relates to the driver’s side crash sensor, mounted behind the front bumper.
From the notes you posted it looks like they’ve been pretty thorough and looked for wiring damage and connector corrosion which would be the initial things to check. But as the fault has returned, I’d say it would perhaps point to a failed sensor.
This is an example replacement part, so you have an idea:
Firstly, that’s good news.
This is clearly one of life’s little mysteries!
Obviously one Mazda garage has a different opinion to another and perhaps like MOT centres.
Also like us too and thanks for the update.
Wanted to run a line-in to my amp tomorrow . Trouble is, searching a diagram for MX-5 amplifier gave me an MX-5 guitar effects pedal and an ND4 is a Bass guitar amplifier. Found this bonnet code diagram though thanks to my iphone telling the search engine what I’m browsing.
Count the red light flashes and match the sequence, jiggle wires accordingly. Once you’ve stripped half the car down of course.