So, my daughter has a 2002 Honda Civic. Before Christmas her airbag (SRS) light went on. We took it to the dealer and they said it would cost $1000 to fix. We then took it to an independent mechanic. He pulled a bunch of my daughter’s crap out from under the seat, reset the computer and took it for a test drive–everything was fine.
The Mechanic said two things might have caused it–1) the pile of crap under the seat or 2) modern electronics. He said on older cars, putting a cell phone or tablet on the passenger seat interferes with the sensors talking to the computer. This essentially confuses the computer (my words not his) and the computer reports that the SRS is not working. This sounded whacky to me so I googled it and sure enough, found similar complaints/instances where there was a false report of SRS problems due to cell phones on passenger seats. How do they know its the cell phone? One report actually cited a test. Another guy was told by a Honda dealer to either shut off the phone or pay $1000 dollars to get a “fix” installed. Apparently this is also a problem with Mercedes.
My question is, what could be the mechanism that causes this? Are the cell phones inducing a current in the wires that mimics a bad sensor? Does the sensor send status via RF to the computer instead of wires (I find this unlikely)? Any ideas?
FYI: there is a massive Honda recall for airbags right now.
The SRS system has multiple sensors: seat belt latch, seat belt tensioner, the momentum sensor(?), seat sensor, and others.
I’m thinking that the seatbelt sensor is being confused by the cell phone that is lying on top of it. In a city, with many cell sites, it may not be an issue as the cell phone will be transmitting in a low power mode. But, as you go out to more open spaces the cell’s can get larger and more power is required to transmit. Obviously, there is enough transmitted power to generate an EMF that is impacting the sensor in some way. Another real possibility is that the sensor is in effect acting as an antenna and picking up the RF and without proper filtering on the SRS control unit itself, is having all kindsa stray EMF/RF coming in causing a fail condition.
I honestly think its that second option that’s the issue.
Cell phones transmit radio signals (that’s how they work) which get picked up by any nearby wires or electrical conductors. Other things that transit do the same thing (walkie-talkies, cordless phones, etc) but cell phones are the biggest transmitter that most folks tend to be commonly carrying around.
The same thing happens with cell phones next to computer speakers, especially active speakers that have amplifiers in them. RF noise from the cell phone gets coupled into the audio path through the wires and amplified by the speaker’s amplifier into audible “chirping” noises. You can often tell when your cell phone is about to ring if you place it near computer speakers, since the speakers will chirp as the phone communicates with the tower to set up the call, so the speakers will start chirping before the phone rings.
Modern electronics are more likely to be shielded specifically against cell phone signals. Older stuff and cheaper things (like computer speakers) tend to be less shielded.
In your case, the RF noise generated by the cell phone is interfering enough with the signals from the air bag sensor that the computer is getting confused and thinks that there is a problem.