Another warning indicator that may illuminate on your dashboard is the dreaded air bag light. These airbag problems can be much more complicated to repair than let's say check engine light problems.
The airbag specialized scan tool pictured to the right is an expensive piece of equipment at around 4 thousand dollars. They do make several SIR (Supplemental Inflatable restraint) code readers that are under $200.00 but the problem is they do not cover all vehicles.
On some cars when a malfunction is detected the light will continually flash codes. On others the light might be steady until a diagnostic mode is entered. To be honest it's a mess because it is not standardized. I recently diagnosed and repaired a Toyota Corolla with a steady flashing light with no codes. I'll add this story at the bottom if you're interested.
For domestic vehicles they have the OTC 9450. This thing can read and erase OBD II codes plus display and erase ABS and Airbag trouble codes.
The on-board code library feature provides definitions on screen of pulled codes. A big point to make is that the ABS and Airbag functions are limited and will not work on all model cars and trucks. OTC states it works on most domestic vehicles 1996-2008.
Two things to make clear. The scanner can be used to read and clear codes but it is recommended that servicing of this important safety system should be performed by professional technicians. Second, is that coverage is spotty but I show the tool because if your vehicle is covered this multifunction unit is handy.
The next lucky group of people that would have access to a cheap scan tool that can read airbag codes is the owners of German cars of the 90's. Specifically the Volkswagen and Audi models.
If you own a modern Volkswagen or Audi you can read many codes including Engine, Transmission, Airbag and ABS. The Roadi scanner is designed to read VAG system trouble codes on 4 systems. The code definitions display right on screen. It works with Volkswagen and Audi's from 1990 or newer.
Supplemental restraint systems (SRS) have been deployed since the 80s. The problem of the illuminated air bag light is becoming more common on these aging cars and trucks. It is for this reason that I decided to write a quick article about what I find most often causing the light to flash or stay on.
Keep in mind that these are very complicated systems and many things can cause the warning light to flash, stay on or not come on at all. Communicating with the control module is often required. Some manufacturers require a scan tool for diagnosis.
Other manufacturers automatically flash the code from the dashboard warning light. You'll have to get an auto service guide for your specific model to determine how to read the flash codes because procedures will vary greatly between companies.
This dashboard mounted indicator is designed to let the driver know that the system is ready to do its job. Of course this would be to deploy the quick inflating bag during a hard collision. On most vehicles the lamp is operated by the main control module.
The light should illuminate when the key is turned from the off to the on or run position for a bulb check. On some models the light will flash briefly while the system runs a complete diagnostic. But when the engine is running the light should go out.
If a malfunction is uncovered during the quick automatic diagnostic test the airbag light may stay on continuously or even flash. This could mean a problem that would prevent the airbag from deploying in the case of an accident. For this reason diagnosis should be performed as quickly as possible.
One of the components that get a constant workout in any SRS system is a part that most mechanics will call the clockspring. The airbag clock spring allows for constant electrical contact to the steering wheel mounted module and related components at all times.
The clock spring is located between the steering wheel and the steering column and contains a conductive flat ribbon that maintains this needed contact during steering wheel rotation. This important component feeds power from the vehicle's battery up to the module and is ultimately responsible for providing the needed energy to deploy the bag.
If electrical contact should be disrupted between the module and the airbag clock spring a code will be set and the air bag light may flash to indicate that there is a problem.
Since this is one of the only components that are constantly moving in the SRS system it is also one of the most common failures.
Replacement of the SRS clock-spring requires the removal of the airbag assembly and the steering wheel as well. Some special tools may be required to complete the repairs. Accidental deployment when removing the air bag is not common but is possible. For these reasons it's best to have it replaced by a qualified car mechanic.
Diagnosis of many air bag light faults is impossible without some special tools. On Ford vehicles from the late eighties well into the nineties a special tool called a simulator (pictured to the right) is used to aid in diagnostics.
Because the circuit remains open when you unplug the module many testing procedures cannot be performed. The simulator provides the correct resistance and specifications as a good part would. This allows the diagnosis to safely continue.
The Ford special simulator tools are essential for body repair shops but can also be helpful for mechanics trying to diagnose air bag lights. Some diagnostic tree charts in the ford service manual require the use of one of these air bag simulators because they will simulate a complete circuit for diagnostic purposes.
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I had a 02 Corolla come in with a flashing warning light. As I sat there trying to count the flashes I realized that it was not indicating a stored code but rather it was stuck in initial diagnostics. There was no pause in the flashes to indicate a 2 digit code.
When you turn on the key it goes into an automatic self test mode. Basically the module sends out a reference signal to all of the sensors and actuators and waits for the return voltage. On this Toyota corolla it never got the return signal.
The reason was the wiring harness had high resistance. A friend of mine that works at a dealer gave me the heads up on this so I can't take credit for it. If you have a Lexus or Toyota with problems in this area there is a quick learning guide available in many different formats including Kindle, Android and MP3. Often you can't use normal diagnostic procedures when dealing with these pyrotechnic safety systems. Therefore seeking out specialized information is recommended.
The homepage is still the best place to go for a run down of the massive amount of information covered here. You can find many answers to car questions on the auto-facts.org Homepage.
More articles about dashboard warning lights and common problems that cause them are grouped on my auto scan tool page. This next link will take you there from this page about the air bag light.