Airbag ECU code 31 - what does it really mean?

[ajuniper]

My mothers Yaris has just turned its airbag light on for no obvious reason. The car's not been involved in an accident.

Jumpering the connections on the diag connector gives code 31 which concurs with the Toyota diagnosis of wanting to replace the airbag ECU for a large sum of money.

What does this code 31 really mean? Is it normal on the Yaris for the airbag ECU to just fail like this, or is it more likely to indicate a wiring problem somewhere? If so, what connections need looking at, and which are safe to check with a voltmeter / ohmmeter?

Are there any instructions anywhere for extracting the airbag ECU?

With symptoms like this, is sending the unit away for a code reset likely to be a proper fix, or is the code likely just going to keep coming back?

The car is a July 2004 UK model French built Yaris with a 1SZFE engine.

thanks
Andy

[CTScott]

31 is a general failure of the SRS ECU. It is located under the center of the dash. I have not accessed one on a MK1, but on a MK2 that means pulling the center console assembly and A/C controls to get to it.

Other than checking to make sure that the connectors are properly latched, there is not much else that you can do besides replacing it. Used ones can be inexpensive from junk yards or off ebay, but one which came from a wrecked car, where the airbags deployed, will need to have its crash data reset (otherwise the SRS light always stays on, with no codes).

[ajuniper]

Thanks for the prompt reply.

Is there any chance that the fault code could be induced by e.g. a wiring or earthing fault? I'd hate to go about sourcing a replacement ECU only to find that the problem wasn't in the ECU at all.

How likely is it that having the ECU "reset" will be successful? Do these ECUs suffer from transient faults or is this code likely to be terminal?

thanks
Andy

[ajuniper]

PS. For anyone else with similar issues, further searching led me to find this page where I found a number of Mk1 Yaris manuals...

http://www.toyotaownersclub.com/forums/topic/97062-yaris-chassis-body-electrical-and-service-manuals/#entry1252866

Including details on how to remove the airbag ECU :-)

[CTScott]

Thanks for the prompt reply.

Is there any chance that the fault code could be induced by e.g. a wiring or earthing fault? I'd hate to go about sourcing a replacement ECU only to find that the problem wasn't in the ECU at all.

How likely is it that having the ECU "reset" will be successful? Do these ECUs suffer from transient faults or is this code likely to be terminal?

thanks
Andy

You can actually try resetting it yourself using the procedure below. I have never heard of anyone having that particular fault, so it is not common. As for being a wiring or ground fault, I would suspect that more than just that ECU would be having issues if it were.


For MK1 Yaris built in France after 11-2002, the procedure to reset the SRS light is:

http://i372.photobucket.com/albums/oo163/ctscott329/srs_zps84ff80b4.jpg (http://s372.photobucket.com/user/ctscott329/media/srs_zps84ff80b4.jpg.html)


1. Jump the CG and TC pins (Shown in the post above about reading the codes).

2. Turn the ignition to ON

3. Remove the jumper within 10 seconds after the airbag light begins to flash to show the stored codes.

4. Within 3 seconds of disconnecting the jumper the airbag light should light up.

5. Within 2 to 4 seconds after the airbag light comes on, reconnect the jumper between CG and TC.

6. Within 2 to 4 seconds after reconnecting the jumper the airbag light will go off.

7. Within 2 to 4 seconds after the airbag light goes off, disconnect the jumper between CG and TC.

8. Within 3 seconds of disconnecting the jumper the airbag light should light up.

9. Within 2 to 4 seconds after the airbag light comes on, reconnect the jumper between CG and TC.

10. Within 2 to 4 seconds after reconnecting the jumper the airbag light will go off.

11. 1 second after the airbag light goes off the light will flash to indicate the code cleared

12. Turn the ignition off and if more than one code was reported, repeat the procedure to clear the additional codes.


This procedure can be tricky to do, so I recommend creating a jumper with a momentary normally open push button switch, so that you can simply press the button at the appropriate time, rather than having to keep reaching under the dash to make or break the connection. This switch assembly is simply a switch connected to two pieces of wire, with the other ends stripped. If the wire used will not stay seated in the connector, strip a bit more insulation and fold the tip of the wire in half to create a larger "terminal" to insert into the diagnostic connector.

[ajuniper]

Thanks for the detailed info.

I'll have a root around in the bits box for a push switch and have a try at that on Saturday when I am next with the car.

I guess that I'll also take a DVM to check the power and ground connections too...

[ajuniper]

The code cleared down successfully on my second attempt at clearing it. After taking the car for a quick test drive, the ECU is still behaving correctly.

Not sure why the main dealer couldn't / didn't do that as part of investigating why the light was on... and just wanted to replace the ECU for £450...

For the record, the part number of aurbag ECU is 89170-0D100.

Thanks for all the help and guidance, hopefully this thread will help save someone else some money.