Mechanics

ES350 INTERMITTENT AIRBAG WARNING LIGHT.

2009 Lexus ES 350 • 40,000 miles

Car was wrecked and rebuilt, replacing all airbags, airbag control module, clockspring, and all four seat belts (tensioner end only). No airbag light for several months, now suddenly an intermittent light: on one time I'm driving, off the next. Scanned and found no SRS fault codes. How is it possible to have an intermittent airbag light, especially when there's no fault code stored? Is it possible the tensioner side of one or more seat belts is causing this? A loose connection? Thanks!
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Dwafford
October 24, 2011.



The whole idea of stored diagnostic fault codes is to aid in diagnosing intermittent problems such as this. Finding no codes suggests they're being erased due to a power supply problem, meaning loss of 12 volts to one of the terminals on the computer. There will always be two 12 volts supplies. One is needed to power the warning light when the other one is missing. On most cars, either circuit will keep the fault codes in memory, but if the constant "memory" circuit is dead, the codes will erase when you turn off the ignition switch which turns off the "switched" 12 volt supply. Some car brands retain the fault codes in memory even if the computer is completely unplugged. Those codes can only be erased by connecting a scanner to erase them electronically.

I would start by looking for the two fuses for the air bag computer. Be sure they're tight in their sockets. Try wiggling them while watching the air bag light and with the ignition switch turned on. If the light turns on while you're driving, make you way to the dealer or a mechanic with a scanner that can access the air bag computer, but don't turn the engine off. The code(s) should stay in memory as long as the ignition switch stays on.

Caradiodoc
Oct 26, 2011.