99 airbag light, still.....

The jeep has had an intermittent airbag light Forever now.

fyi, Any work done was always after disconnecting the battery and waiting a long time after doing other work.

I have tested the wiring "HARNESS" to pcm (DO NOT TEST THE AIRBAG), for continuity, it checked out. I then unplugged each airbag and drove around. The passenger bag was the one causing the light. I then replaced the passenger airbag with a 2 ohm resistor and this to prevented the airbag light. Just recently Ide found a passenger airbag in the JY and replaced it today. The friggin light is still there!!!

So now I'm trying to understand what else this could be, airbag control module?, pinched wire?

Have I missed anything in trying to diagnose this myself?

Thank you in advance if you can offer some assistance.

I am curious about this myself. Had an airbag light forever in my 2000.

The natural assumption is faulty passenger airbags.

A simple test is to find another XJ with the airbag light not illuminated and swap passenger airbags.

Or, have the airbag codes scanned.

Tim_MN said:

The natural assumption is faulty passenger airbags.

A simple test is to find another XJ with the airbag light not illuminated and swap passenger airbags.

Or, have the airbag codes scanned.

Click to expand...

Tim,

If the fault is a passenger bag, would the codes just say a passenger airbag I'd faulty?

If it's a wiring issue, would the scan simply tell you the issue is with the wiring, or will it be more in depth to suggest it's ground related?

I have never had airbag codes scanned, so IDK the detail provided. I do believe that the ground for both airbags is at the control unit under the center console based upon the wrecks I have repaired.

Can anyone please provide details on what type of information is provided by a scanner on airbags for obdii vehicles? I'm simply trying to learn what takes place when a tech would be trying to diagnose this, and what the scanner would provide.

Thank you in advance

That would totally depend on the scanner, my son's Matco reads/diagnosis all the sub-codes but it cost 4k$.

So is it safe to say as long as the airbag light is illuminated there is a code?

That I'm not sure of as the ACM reports directly to the instrument cluster via the CCD bus.

thank you for the feedback, I know the ACM to ground on the chassis is good, and the wiring up to the airbag read fine when I checked for continuity, much to my dismay of hoping ide see something.

Are there no techs or experienced folks with high end scanners in here that can speak to this?

Substituting the 2 ohm resistor points to a faulty airbag. Sounds like you haven't measured the resistance across the airbag that caused the airbag light. I wouldn't be afraid to do that. Airbags charges are ignited by running a current through the wiring. A resistance measurement using an ohm meter sends a trivial amount of current through the circuit being tested (the airbag). This is simply knowing what the available equipment does. If you are really worried, test it like shown in the first video link. Note in the comments and second video that other people have also successfully ohm tested airbags. Make sure that your multimeter is set to resistance (ohms) before connecting it to the airbag.

https://www.youtube.com/watch?v=88Dxq5_BwnM

https://www.youtube.com/watch?v=Giib-ELOQjY

That is correct I have not tried measuring the airbags resistance, in fear of it going off. It's just a common thing to read of folks not suggesting someone does this. Whether that's a logical caution, I do not know l, which is why I'm asking the wiser on here.

I'll certainly look over these links and see what more I can learn, thank you very much.

I also have a cheap oscilloscope, can this be used in anyway to safely see what might be causing this airbag light?

Oscilloscope probably has no value because the airbag diagnostic logic most likely relies on DC signalling, but if the diagnostic logic used for the airbag system is described in the XJ service manual, you might be able to gain some insight for further tests that you can attempt besides testing the resistivity of the airbag.

With that said, my guess is that the airbag diagnostic logic is the same as that used for the efan, injectors, and coils. The diagnostic logic for these is to probe for the presence of a resistance in a specified range. If the resistance is too high, then that represents an open circuit. If the resistance is too low, then then that represents a short circuit.

My guess is that there are two potential causes of your airbag light: 1) The airbag is toast, i.e., the ignitor circuit is either broken or shorted. The connection at the airbag plug is bad. Testing the resistance of the airbag will tell you which of these is the problem.