Replaced Water Pump,
Join Date: Aug 2009
Location: New Zealand
Yes Rarebear, no doubt that everyone should treat an airbag warning light seriously, and as if the airbags have been disabled.
I am a bit confused however that the 'Main ECU' is involved in triggering the airbags, if by main ECU you mean the Bosch Motronic Unit, or the "Integrated services electronic control unit" which I think is also referred to as the "body ECU". I can't find any mention of this in the DTE documentation. I was looking at the data for 156 Twinspark 2.0.
What DTE Rel 32.2.114 lists as the Air Bag system components under 'Description and Operation>55 electrical equipment>5580 special accessories>5580C air bag system>information not connected to choice of accessory>System components' is the following:
1. Electronic Control Unit (Identified in the diagram as located atop the transmission tunnel, next to drivers feet)
2. Drivers Air Bag
3. Passengers Air Bag
4. Left seat belt pretensioner
5. Right seat belt pretensioner
6. Switch disabling passenser airbag
7. Passenger airbag automatic disablement sensor
8. Diagnostic socket for checking system
9. Warning light for instrument panel
10 Warning light for signalling passenger airbag disabling
No other ECU is listed as part of the system, which if it decided whether the air bags are to fire you think be included.
The operation of the "Electronic Control Unit "is descibed at 'Description and Operation>55 electrical equipment>5580 special accessories>5580C air bag system>information not connected to choice of accessory>Electronic control Unit>Operation' as follows:
"Inside the control unit, there is an accelerometric sensor whose signal, suitably processed by a microprocessor makes it possible to determine the severity of an impact and consequently to decide whether or not to activate the airbags. A second sensor with safety functions gives enablement for the activation of the air bags. The control unit has two different intervention levels: at the the first level only the pretensioners are activate the second level operates both airbags and pretensioners. The control unit only detects frontal impacts. In the case of side impacts, collisions or the vehicle overturning, it does not activate the system"
Both the pin out assignments for the airbag Control Unit (M60) and wiring diagrams for the airbag system show no interconnection with any other ECU. The pin 9 "line K" of the 30 pin connector connects directly to Pin 3 of the OBD-II connector. All sensor and airbag and pretensioner activation circuits run from the Air Bag Control Unit and appear to be only controlled by the microprocessor located on the PCB within the unit.
The wiring diagram also shows that the air bag circuitry is supplied power by the ignition switch via a fuse to pin 12 on the 30-pin connector. The airbag warning light is supplied on seperate circuit from the ignition switch via a seperate fuse, but its status is controlled by pins 13 (main air bag) and 20 (passenger airbag) of the same 30-pin connector to the Airbag Control unit. Note this circuit is independent of any other ECU on the vehicle.
With the Air Bag Control unit removed the main warning light is earthed and will glow continuously. For the light to be off or to go on for 4 sec, turn off and then on again if a fault is logged, requires power to the Air Bag Control Unit. Thus a warning light is not indication that no power is being supplied to the Airbag Control Unit, which if the fuse (F5) is intact is supplied continously when the ignition is on.
So is there a seperate ECU or is the crash sensor (which is what is printed on the unit) also the the Airbag ECU, which is what is is called in DTE, or more correctly the crash sensor and ECU are housed within the same unit.
Darryl in New Zealand