Ok so my airbag light has been on for the last 3 months. It turned on and stays lit. It never flashed. It turned on right after I tried to tune my CB radio. I checked all the airbag connectors. I started researching it online and I read an article mentioning that if the electrical signal going to the ABS module is altered in any way (disconnected or even just slightly weakened) it will set a code. Possibly a "hard crash" code that requires the module be sent away to be reset.

That got me thinking about the CB radio again. I ran the coax to the antenna down the drivers side under the trim molding along the floor to the rear of the truck. If I am not mistaken the airbag module is under the driver seat and the wire harness runs under that same trim molding.

Would the signal going through the coax next to that wiring harness be able to alter the electrical signal going to the airbag module?

I heard the chime when the airbag light came on as soon as I hit the transmit button the first time on the radio to tune it.

Hopefully there are some knowledgeable CB guys out there...

 

The answer to your question is, no. How did you run power to your cb? A cb should be wired directly to the battery, both positive, and negative with a 20 amp fuse on the positive side.

Don't know what else you could have done during the cb installation. I would disconnect the battery for a minute or so, and see if it resets the computer. You might want to double check all of your wiring harnesses to make sure they are connected properly. Good luck.

 

I wired it by using the fuse block under the dash. I used two unused power points. One point having constant 12 volts and one to 12 volts only with the key on. The positive wires are fused.

I tried disconnecting the battery for an hour, the airbag light came on when i turned the truck on as if it never even cleared.

 

You don't say what year or engine, etc your truck is. But on mine, the ABS module is not under the seat, it is on the hump under the instrument panel, and the wiring runs down the middle of the truck.

It might help to check the codes in the ABS module. That might give you some more information.

 

I don't understand why you have two power supply's going to your cb. The back of your cb should only have two wires coming out of it, a red wire, and a black wire. Both of those wires should go directly to the battery, with a 20 amp fuse on the positive side.

 

My Cobra CB is that way too. One is hot always and the other is hot in accy. I think the hot always is only for maintaining the "memory" of the CB such as what channel you're set to, etc.

 

Well, I guess they are all different. I just hooked up a Cobra 29 LX LE a few weeks ago, and it only had two wires coming out of the back. One wire was red, and the other was black, same with the amp as well. I ran both wires straight to the battery, with a 20 amp fuse on the positive side, the cb even had a 2 amp fuse also, which I changed to a 5 amp. But the cb, and amp are directly wired to the battery with the same wires, so I only passed two wires through the firewall. It seems strange that he tries to tune his mic, and the airbag light comes on. It makes me think he wired something wrong, or didn't ground it properly.

 

its an 04 f250 5.4. Yup it is a cobra radio that uses the second power wire to retain the channel memory. The wire to the acc. is so the radio comes on and off when i turn the truck on and off.


I kinda assumed it was under the seat so I could be wrong. The thing is i installed the radio and coax one month before i hooked the antenna up and tunned it. So for a month there were no airbag issues untill i turned the radio on and tried to transmit.

I guess i will have to take it to the dealer and have them pull the module code.

I checked along every inch where i ran the coax looking for wiring and connectors I may have disturbed but have found nothing.

I appreciate the help guys.

 

the coax is the culpret. You might have to upgrade to Superflex or one with a 98 percent rated shielding.
Also where it is routed has an effect, you will have to route the coax away from and not close to any of the trucks wiring.
RF has very unpredictable results in these computer driven vehicles.

My Ford Thunderbird's windshield wipers would activate when I keyed up my mic. So what you are experiencing is not uncommon.

 

Thanks benchwrench. At first I didnt believe that the coax could be the culprit , but after awhile I just had that feeling. I'm no radio expert but I have a general knowledge about them and knew that a signal running through the coax does emit an electrical "field" so to speak around it. I just didnt know how powerful it is.

But hell if it would flip the relay to run your wipers, lol I can def. see it playing with my airbag module!

Oh and can someone confirm where the airbag module is in an 04 f250?

I assumed it was under the driver seat because thats where it has been on other vehicles I have worked on. If it is under the dash, well my coax runs right under the driver side dash too.

Thanks for the help!

 

If you want a sure fix, go for your amature ticket. Much better way of comm. than 11 Meters.

 

Check out how you mounted it, Dave says that the module is on the hump and runs down the middle, you may have ran a mounting screw thru the wire and when you keyed it up,sent a sig. thru the ground into your ab wires.
I also have my coax ran under the dash and under the trim to the rear of the cab, but all I get is a little radio interference when I crank it up.

 

Absolutely, yes, the CB coax cable can emit a pretty strong electric field that would induce "noise" in other circuits. The techno-speak term for it is crosstalk.

To eliminate, the solutions are space and/or shielding.

Better shielding of the coax will better contain the field. Use better coax, or if you are redneck enough, just try wrapping the coax in aluminum foil with the foil making decent contact to ground (bare metal on body).

The strength of the field drops dramatically with distance from the coax. Doubling the distance between the coax and the circuit it is inducing noise into will reduce noise by 75%. Triple the distance, 90%. Re-routing the cable on the other side of truck may fix it.

 

This is what I have on the location of the module.

 

Thanks for the input and the diagram. That definately confirms it. The wires that run to the drivers side belt tensioner run under the floor trim where I ran the coax. The "crosstalk" must have sent a signal through those wires to the Airbag module and made it think that the belt tensioner deployed. That would explain why the airbag light is constantly on and will not clear by disconnecting the battery for 24 hours.

Im going to take it in to read the code to be sure before i send the module off to be reset. Then I will be re-routing my coax! I will probably upgrade to some quality coax too just to be safe.

I wasn't even thinking about that when I was routing the coax. All well, lesson learned.

Thanks again

Dan