Let me start over again, with more accuracy.
Her work bill states:
Troubleshoot 9223-airbag resistance high- but all sqibbs resistance too high
Cannot inspect SRS control unit because aftermarket radio glued in and has broke dashboard. May need SRS cu.
Can someone translate this for me; why would all the resistances be high?
She says she will have to break into the dash to inspect the SRS unit and then probably replace it.
Okay, we're getting more of the story, and that is helpful.
The SRS Module has individual sensors that monitor each component of the Supplemental Restraint System.... each Airbag, each Seat Belt Latch, each ETR, and the Passenger's Seat Pad.
If ALL the sensors were reporting back that the resistance was too high on every component, the SRS Module would have reported an entire series of Fault Codes. But, from what you describe, the only fault code was 9223.
The 9223 code
points to a fault in the Driver's door side air bag
or the wiring harness
from the SRS Control Module to the airbag.
More often it is the wiring which is at fault, and not the air bag itself.
You will need to remove the driver's door liner and install a 3 ohm air bag substitution resistor, in place of the air bag, and erase the fault code.
If the 9223 code returns, then the fault is in the wiring
to the air bag.
If the 9223 code erases and does not return, but it returns when you plug the connector back into the air bag, then the fault is with the air bag itself
Additionally, the airbag's squib, itself, can be tested with a multimeter SET AT THE LOWEST OHM RESISTANCE. EXTREME CARE IS REQUIRED
when testing any squib.... if the multimeter is not set at a low Ohm test, the voltage from the multimeter can trigger the squib and severe injury can occur. I have successfully tested an ETR squib this way, and found that it was faulty.
On Replacing the SRS Control Unit
If the SRS Control Module, (also referred to as SRS Control Unit) was faulty and needed replacing, two things would occur:
There would be a specific Fault Code for it, like a Code 'B2D97'. Restraints Systems Control Unit is defective.
If the SRS Control Module was faulty, and needed to be replaced, it would not be able to monitor any of the sensors, and it would not be capable of giving a 9223 Fault Code.
Based on the information you provided, I do not think your mechanic is competent
in being able to properly diagnose your vehicle's problem.
Telling you that the SRS Control module needs replacing at $3,000 is just "BULLCRAP"
as Blake Shelton would say.
Take your Mercedes to a garage where properly trained technicians have the proper diagnostic equipment and know-how to fix your problem.
Hope this is of help.
God Bless, Arctic