Frame rail airbag sensor wiring/computer problem

Hi Terry,

I suggest that you download the electrical wiring diagram for your model year from techinfo.toyota.com but in an effort to help you assess the problem I've attached a few relevant pages from the 2006 EWD. Note that in this diagram, the side airbag sensors have black and white colored wires.

Also note that the wires run to the SRS ECU. If you want to determine whether the problem is the wiring harness or the ECU, then you would have to measure resistances at the appropriate ECU wiring harness connector pins to see if they differ from what you measure at the sensors. If no difference, then the problem is at the ECU. If a difference, then the wiring harness is damaged.

I hope that you are using a digital multimeter for your resistance checks. If you are using an inexpensive VOM, the battery current used for resistance checks may damage delicate electronics.

 

also you need a wiring diagram to check out everything, where exactly was it hit?

mine luckily didnt have issues with the airbag connectors, i just had to replace airbag sensors and SRS ecu

 

Hi Terry,

Yes, your meter should be OK to use. I don't know how the Snap-on tool works so I can't say whether this will help or harm.

Regarding the varying resistances that you've noted, I suppose you could disconnect the wiring harness connector from the SRS ECU and the connectors leading to the sensors. If you measure resistance from the sensor connector pins to ground I'd expect an infinite resistance. If you measure some finite resistance this would imply damage to the wiring harness.

If you can determine which pins on the SRS wiring harness connector correspond to the sensors, then measure resistance from one connector to the other to see if the wire in between is sound; resistance should be very close to zero. If not, again this implies wiring harness damage.

 

are all the other airbag modules unplugged? they need to all be unplugged before you start testing anything in the airbag system. an ohmmeter testing resistance puts a current into the airbag wire. this is dangerous. and you can burn a computer doing this. that's why the dealership will not test wiring and wants to replace- you can if you make absolutely damned sure EVERYTHING- computers, modules, sensors are all unplugged.

 

Terry

I don't think you can do a Techinfo subscription from Canada. I tried several years ago, it refused to process my Canadian credit card

I went with the All Data subscription instead

Since you're on your own with this one, I suggest a good Digital Multi Meter, eg a Fluke with very high impedance. The FSM and the All Data source have correct troubleshooting procedures

Never, ever check electrical wire resistance with electronics still hooked up, especially airbag modules. You can fry the electronics, and pop the airbags.

jay

 

Without a manual I am just guessing here (yup, I am also in Canada and can't download from techinfo - and I'm NOT paying Toyota Canada $400+ for manuals!!!).

Usually pyro circuits are NOT grounded, either side. This is to prevent RF from setting them off. They are "twisted pairs", in which induced voltages cancel. This should tell you, from the measurements you have already made, which wire is shorted.

 

I think that Terry was measuring resistance on the sensor wiring that tells the SRS ECU when to fire the airbag; not on the wiring that leads to the airbags. The repair manual says: Use a volt/ohmmeter with high impedance (10 k ohms/V minimum) for troubleshooting electrical circuits of the system.


Fluke for example, rates ohmmeter impedance at 50M ohms. Here's the spec sheet for the current version of one of the Fluke DMMs that I own:
Fluke 80 Series V Digital Multimeters)

I would expect any reasonable digital multimeter to have ohmmeter impedance measured in the millions of ohms so the OP should be OK. However I agree that the wiring leading to the airbags should be treated with caution, as no one needs to have an airbag blow up in his/her face.

I believe that Terry indicated that the SRS ECU was replaced. Since wiring harness damage is suspected, there's more reason to disconnect the connectors on the ECU end and the sensor end of the wiring harness and use the ohmmeter to measure continuity and ensure no shorts to the body. Then there's no risk in damaging the ECU or triggering any of the airbags.

 

universally, it is safe practice to ALWAYS ALWAYS ALWAYS disconnect EVERYTHING in the airbag/srs system prior to doing ANY diagnostics of wiring. people get killed by airbags blowing up on them during repair. techs are deadly serious about this stuff when they approach it. there is no other way to do this, and no excuses. you ALWAYS err on the side of extreme caution when the alternative can flat out get you killed.

 

Honestly, I don't like "education" like that, as it hits my pocketbook too deeply. I'd probably just consider the car Tango Uniform and push it off a cliff ...