A fairly routine operation for a common fault.
The SRS warning light was flashing intermittently, (more often than not), with a DTC for Driver’s airbag circuit failure.
Now with some vehicles, the serial data will allow us to look at the resistance of each igniter circuit. This may only be allowable via the manufacturers own equipment, but usually if the data is available to them, a good after market tool will also show it. This vehicle did not allow this data and so I used the scope to analyse the live cicruit.
*WARNING*
Do not do this if you are unsure about what you are doing.
If you look at the following image; you can see the interference in the signal when you use the ‘Maths’ channel. You would definitely be forgiven, for not noticing it in the direct channel signals.
This next image illustrates the difference between good and ‘open circuit’. It helps to really see what happens.
This technique is really useful when you have no access to serial data.
The fault with this vehicle was very changeable when you turned the steering wheel. I have measured these before and found high resistances as opposed to ‘open circuit’ conditions.
A new ‘Clock spring’ (rotary coupling), will sort this problem.
Mark Stammers Diagnostics 