I have yet to play with mine missing a 10 mm socket

Maybe in the morning

 

I’m still fault finding, does anyone know what this symbol from the service manual means?

 

Transient Voltage Suppression Diode or Gunn Diode ?

 

I’ll look into what those are and see if I can find one amongst the wiring. It was in a place in the circuit, where there was a connector, and if you disconnected the connector, the two pins were bridged, but I’ve got no idea if that’s got anything to do with the symbol.

 

Ok, after a bit of research, I think the symbol is the for the airbag shorting bar. Now that makes sense (although I’m not an expert). So when the connector is disconnected, it will short the pins it’s between.

So when I disconnect the connectors from the module, and check each pin for continuity with ground, pin 23 (safing sensor monitor return) is shorting to ground somehow. I don’t think it should be.

I also measured continuity to ground on pin 2, but with the connector out, I think that’s as expected, as it will short to ground via the shorting bar with pin 3.

Next step is to remove the ECU and inspect the safing sensor. Any tips on how to safely remove the ECU, I don’t want to damage it……

Bit of a learning curve, but getting there slowly.

 

Looks like the 2 / 10 mm bolts under the bracket angle

Probably best to remove and install with the battery disconnected

 

Check the # 16 fuse in the trunk

This fuse relies on the trunk fuse box relay to close

With the key in the run position with the engine not running , remove the relay and you should feel it click back open

Fuse 10 , 12 , 14 , 16 rely on the fuse box relay to close , 1 - 9 bypass inside the relay box the relay so they are directly wired to the battery

This is the same case with all fuse boxes

 

I’ve found and repaired the short, I think it was actually the safing sensor feed. In any case, I can’t find a short on either of the crash impact sensors or the airbags. The manual doesn’t indicate a safing sensor short will blow the thermal fuse, but it’s the only short I can find.
Has anyone blown the thermal fuse with a safing sensor short before?

 

I found a fresh pickings x300 arrival at the salvage yard I use

Based on the bags not being blown or any crash damage it is possible to use the components ( ECU , safer sensor , 2 front crash sensors ) to test myself for findings or ship to you

In any case I may need it myself

 

Thanks Parker, really appreciate the offer to grab some parts and potentially ship them out (getting parts in New Zealand has its challenges), I might take you up on the offer, but at this stage, I think I'll be OK. I’m almost certain I’ve found the short I just need to put evening back together and hope for the best! I’m sure this would be easier if I could read the fault codes, but probably less fun, and certainly less educational!

 

OK, I’ve tested everything I can, repaired an intermittent short in the safing sensor wiring, and have come to the conclusion, that I need a new module.

Oh well.

 

Thought it was worth closing this one out. Here’s the sequence of events and what I learned:

1) Airbag Light came on, did as much fault finding as I could (at the time), other than the blown thermal fuse, no other fault found.
2) Replaced the thermal fuse, light went off for a trip, then, back on.
3) Thermal fuse blown again. More fault finding, including testing every sensor for shorts. The safing sensor was shorting to ground (this wasn’t listed as a cause of the thermal fuse blowing in the diagnostic manual).
4) Fixed the short, replaced the thermal fuse again, installed a temperature monitor on the fuse. When the ignition was turned on, the temperate increased rapidly, indicating that there’s still a problem.
5) Replaced the module with a second hand module, everything working fine now.

I have no idea if the original issue was the safing sensor, or the module, but it’s sorted now. If I had to guess, the safing sensor fault caused a secondary fault in the module.

What I learned: There are a number of shorting bars in the airbag system, if you want to check if sensors are shorting to ground, understanding where the shorting bars are, and how they work is important. As far as I can tell, they bridge two pins when a connector is disconnected, which can lead to unexpected results when fault finding with the connectors off. If you look at the connector, you may be able to work out where they are, and how they work.

 

Very helpful N Bath thanks

i hope to avoid this much work but the insight into troubleshooting the beast is illuminating

 

N Bath - I appear to be having the same issue as you with the voltage feed/return on my safing sensor. You mentioned you repaired some shorts in the circuit? Were these actual damaged wires and if so - where were they shorting at? Would like to check mine in case there's a particular problem area for any wiring before locating a new sensor or control unit. I haven't found any visible wiring damage yet.

Thanks!

 

Hi, from memory, when I looked, the wires leading to the safing sensor were bent very sharply around either the ECU or a bracket next to the ECU. It was hard to see the actual short, but when I was inspecting the wires, a saw the faintest flash of copper, and fixed it.

If you know which wire is shorting to ground, that will help.

There’s a picture in the thread above of where the safing sensor is located. I would be interested to know how you get on.

 

Yeah, I've pulled the safing senor out of the kick panel area already. As soon as i pulled the plastic kick panel back and saw the unprotected wires disappearing behind the ECU i was concerned. The connector for the sensor was really wedged in there and took some heavy manipulating to get free. I'll have to inspect the body side of the harness with fresh eyes here. Poor design decision to have the plastic yellow loom stop before an obvious pinch point. On a safety system nonetheless....

 

Good luck. For me, as soon as I had taken the sensor out, I was no longer measuring a short to ground, and the fact that I could see the wear on the wire was a giveaway, so an easy fix.

What confused me a little is that from my read of the manual, that short shouldn’t cause the thermal fuse to blow, but I think in my case it did.

 

Just wanted to update this one - you can see my safing sensor thread in the main X300 forum for more info. Issue appears to have been a blown/leaking capacitor that presumably took out the thermal fuse on the ECM board. I replaced both with comparable units and so far, no more airbag light!