456 - Air Bag Light

What did the SD2 say when it was hooked up. It has a really simple , accurate and direct way of pinpointing the failure. After the ECU the most common failure is the clock spring in the steering column. If it pointed out the issue as the ECU and it could not be reset and a new ECU didn't solve it count me as really surprised. As far as I know new ECUs are not available and if a repaired ECU was installed my money is on it being bad.

 

I threw this together using the pinouts in the WSM...

F456 Airbag circuit

A little rough around the edges... still in development

 

The most common fault is the clock spring behind the steering wheel. Some call it a rotary contact. The air bag ecu looks for a resistance from each airbag, typically about 30 ohms from memory (but I will have to confirm with my data at the workshop). You only have two, a passenger and driver. The passenger is unlikely to be faulty as there is no moving parts. The clock spring moves with all the steering wheel rotations, and is usually the culprit.


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You're welcome

ooops... I just noticed, however, that my mini-graphic of the relay/fuse panel at the bottom of the diagram is for the F550. I corrected that late last night. The lettering and numbering (at least in the WSM and owner's handbook) are different. I also believe that the GTA panel is mounted upside down.


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As always, just click on the original link and refresh your browser if necessary to get the latest version.

Also, there is something weird going on with connectors 45D and 46D. Although they are supposed to plug into each other, the WSM shows one connector has only one wire and the wire with the same colour is in a different position.
To make things more difficult in interpreting the 456 WSM pinout diagrams, Ferrari have mislabelled the connectors. In my diagrams, to make things easier for myself, I label my connectors as per the pinout diagrams, not as per the location guide at the beginning of the each sub chapter.

e.g.

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Hope this makes sense

 

No, the clock spring/rotating contact is a cartridge. It’s basically a printed circuit on a tape. It’s very rudimentary, and hasn’t changed even on today’s cars. The airbag and the steering wheel has to be removed to get at it. The clockspring screws have to be removed BEFORE removing the steering wheel, as it’s screwed to it, as opposed to later model cars. Once you remove the clockspring cartridge, you can check continuity through each of its circuits.
The whole process is pretty quick.


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P.S. I'd be curious to know what the actual car's connector (45D/46D) looks like. It seems to be to the right of the main relay panel, but it may not be easy to find. It looks like it's in the door sill

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Not sure. It seems like an unnecessary change between models. These WSM 3D drawings of cable looms can be a little misleading. It does look like it's slightly to the right of the centre console (but perhaps still within in, and almost under the dash).(EDIT: I just realised you're in the UK, so ... the wiring may run on the left hand side)

I'm surprised that a regular service would have picked up hacked wiring, but I would say that the hack would have been done near the 10F/36F plug if that plug is accessible under the dash. The alternator warning and airbag light wiring runs close to each other in that area, although I still don't understand how they wired it up. The alternator light is the yellow-green wire on F10 pin 8. The grey-green wire for the airbag light is on pin 11.

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Let me know if you need any more diagrams. Note that some of the wires on either side of that F10 plug have different colours. I have some coloured charts which show the wires, but hopefully the Digitek unit is not involved as it would be hard to explain the mistakes Ferrari has made with plug identification on that unit.
If the techs have cut the wiring, you would just have to do regular resistance checks of the circuit on either side of 10F/36F. Some going to the instrument panel, some going back to the Airbag ECU.

You have my sympathies. The previous &%$# owner of my 355 did a similar creative modification so that the Check Engine Light wouldn't come on (for faults), but illuminated during startup as it should. Unmodding the CEL wiring was easy, but I had to change the entire engine harness to fix the problem it was hiding. Basically an engine out job.

 

I guess your instrument harnesses would be a mirror version?

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Warning, this is purely a guess as I am no where near your car.

The warning lights are all connected to 12V supply at one end. Then the other end is grounded by the control circuit to turn the light on. This is also how the control circuit can tell whether the light is connected or not by measuring the current being dumped back to the control side via a current sensing circuit. Although the alternator light does not follow this scheme because its current runs through the alternator to detect whenever the alternator is bad. Therefore, it would not work well as a hack if the airbag light is connected to the alternator light.

I suspect that the service tech was looking for the reason why the alternator light was on and found that it had been connected to the Airbag light and corrected the situation, thereby leading to the Airbag light being on, and then washing their hands clean of someone else's hack.

For this hack to work, it would have to use something other than the Alternator light.

 

As Mitchell says, the common is voltage for most lamps (including the airbag light). The airbag ECU provides a ground for the light. However, I think if you cut the pink wire and hooked up the yellow-green wire (going to the alternator light) to the end of the pink wire, it would behave the same way as the alternator light. It would come on with ignition on, then extinguish after start because the voltages on both sides of the lamp would be equal (zero potential).

However, if the techs removed the hack, I don't know why your airbag light is illuminating, unless your pink wire is shorted to earth somewhere. Or it could be something crazy like the wrong lamp fitted to the airbag light (incorrect resistance)? Does the Airbag ECU put on the light if it senses a faulty light circuit

 

Does the GTA use incandescent lamps or LEDs in the instrument binnacle?

 

I was just wondering if someone had fitted an LED type at some point and this had confused the airbag ECU because the resistance was different. Also, if your ohmmeter probes were back to front, the diode effect of an early type LED lamp might make the ohmmeter see open circuit. I'm guessing the lamps are not so easy to replace, but if you can do that resistance check from the airbag ECU, with the ohmmeter leads one way, then the other.

It's unlikely, but stranger things have happened. When I used to work on aircraft, we had to make sure the test lamps for the fire extinguishant system were the right type as the wrong type bulb might blow the extinguishant bottles when we did a test.

 

Ros- Removing dashes, my favorite thing. Good luck with finding the hack.

 

You can take it out without removing the steering wheel, just drop the column down to its lowest point. Unplug all connectors and slide it toward the steering wheel and then to the right.

As for the switch, does not sound like stock but maybe there is a switch for the UK car. Show a picture.

 

After a little reading...

The switch is found on cars with automatic gearboxes. If the gear lever is not positioned in "P", the ignition key cannot be removed. If this key locking system fails in the locked position, you can pull on this button to remove the key.

Ref WSM "H41"... and I assume it's in the driver's handbook, too?

 

This GTA key lock might be the mystery box in the wiring diagrams adjacent to the ignition key.

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The WSM shows two wires going to the key lock: A black earth wire and a white-red wire. I suspect there is a solenoid of some description inside which activates when the gear lever is in "P". I'll try to dig deeper into that circuit to see what I can find.

 

Sorry, slightly off topic, but that ignition keylock circuit goes to a connector (24D) close to the gear select lever. The wiring diagrams end here. There is no switch shown in the parts manual which might correspond to the Park position. I thought identifying the signals which are going through connector 24D might shed some light on the circuits, but it has a buckload of different data going in and out of it. e.g. signals to/from the instrument panel (Digitek unit), Left Inertia Relay input(?), battery and ignition key power for the automatic transmission, OBD2 and diagnostics, ABS/ASR system connection, etc.

Correction: Grey-red wire