FIRST - WARNING - YOU are attempting to service and repair a potentially very dangerous subsystem of your car. It is UP TO YOU to get the FACTS and continue AT YOUR OWN RISK. This note contains a paraphrased summary of some proceedures from the OEM Shop Manual and are NOT my direction or responsibility. ALWAYS confirm what you're doing by following the EOM Shop Manual exactly.
Okay. I was having some troubles with a friends '90 GM flashing an Air Bag fault code "9" and the help was pretty slim. So,... I've got out and done the leg work to nail Air Bag and Crash Sensor information and here goes.
Primary Carsh Sensor: this is the term used to refer to any or all three of the Crash Sensors in the front ot the car. All three Crash Sensors have White Plastic Connectors and are unique to the commonly found Ford type connectors in appearance and the fact that the connector can be easliy released and unplugged.
Sensor Location & Identification:
LEFT - located in a cut out in the Drivers side inner Fender at the very front of the Fender. Accessed in a '90 GM by removing the Washer Fluid Reservoir.
RIGHT - located in a cut out in the Passengers side inner Fender at the very front of the Fender. Accessed in a '90 GM by removing the Battery.
CENTER - located under the Hood Latch Assembly, behind the Grill and forward of the A/C Condensor.
NOTE: the Crash Sensors have a Green Ground Bolt and function in some way with Chassis Ground so chassis rust might degrade available Ground. It may be helpful to run an independant Ground Wire to the Crash Sensor Bolt, though no such solution is suggested inthe EOM Shop Manual.
Crash Sensor Replacement:
Much confusion surrounds required parts and replacement plans. SOme think that all three must be replaced together, some thinking otherwise.
CV/GM/TC's could have been equiped with Crash Sensors made by either TRW or Bree. The manufacturer can generally be identified by markings on the part.
If your car is TRW Crash Sensors you will need to replace all three Crash Sensors with the Bree parts. The TRW's are long since unavailable and have tollerance problems that make individual replacement impracticle and/or dangerous.
To replace your TRW Crash Sensor set with the Bree parts requires an expensive EOM Kit in the range of $800.
If your car has Bree Crash Sensors they can be replaced individually.\ as follows:
By the time I became involved in this in March 2007, all part numbers have been cancelled by Ford and purged from stock. Aquiring parts is limitted to EvilBAY and those few companies who buy all of Ford's cast off parts like Green Sales and maybe junk yards.
Proper troubleshooting is indicated as with any failure. Use the Factory Service Manual to do this and ONLY if you know precisely what you're doing. The short version is:
1 - discharge the Air Bag System by removing the Posative Battery Cable from the Battery and shorting it to the Negative for 10-25 minutes.
2 - unplug ALL THREE of the Primary Crash Sensors
3 - check each Pin of all three Crash Sensors for 1000-1300 Ohms to Ground.
4 - replace the Crash Sensors that do not pass the test in Step 3
5 - if all three Crash Sensors pass the test in Step 3, check each Pin of the three Crash Sensors Chassis side Connectors. They should measure 1000-1300 Ohms (not sure if that's to Ground or to the Air Bag Module Connector)
6 - after completion of repairs correctly reconnect the Battery Cable and, FROM A POSITION WHERE NO PART OF YOU IS IN FRONT OF THE AIR BAG, Start the car and check the Air BAg indicator light for normal, fault free operation.
Ha, that's a joke right?
The Air Bag Module will "beep" almost constantly if the Air Bag warning light is removed (Open) or is Shorted.
There is no alternative to a complete and effective repair and fully functional vehicles safety system.