I have a new AIU I’m setting up to work with my TIU and WiFi modules. I found out from MTH that the 5v from the WiFi module isn’t enough to power the AIU relays. So, I now have a 15v Wall wart from a starter set plugged into the TIU in addition to the WiFi.

Now, when I program the AIU and select a switch or accessory, I get a “command Failure” message..

Any idea what’s causing this?




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Original Post

Curious how you have all this hooked up?  The WiFi unit can’t/doesn’t power anything else.  The AIU gets its power and commands from the TIU, not the WiFi unit.



The WiFi is attached to a 5v wall wart. The USB on the WiFi plugs into the TIU and gives the board the 5v it needs to operate.

OK, the 15V wall wart you are using to power the TIU; is it AC or DC, what is the power rating, and how do you have it connected? Is it plugged into the Aux Power Input? Sounds like your auxiliary power transformer is not putting out enough power. Any chance you have a Z500 sitting around?

The 15v wall wart is from an MTH starter set. When I talked to Jacob at MTH, he said it should work, but...

I have a Z1000 I use for my Christmas layout I can try if you think that may be the problem.

It won't hurt anything to try the Z1000. It will plug directly into the Aux Power Input port on the TIU.

You didn't accidentally plug the TIU into the OUT port on the AIU, did you? 

Last edited by Gilly@N&W

No Legion, the WIU cannot power the TIU so as to operate anything.  It may keep the TIU board alive, but not usable.  Have you answered Gilly's last question?  That will cause repairable damage.  Depending on its ampacity, a 15-volt WW should provide adequate power; does it allow the TIU to run trains?

I think you’re mis-understanding me. MTH told me the WiFi unit (powered by a wall wart) is powering the TIU board thru the USB. The Z4000 I have is plugged into the TIU fixed IN and OUT jacks I use for my track power. I have been running It that way for about a year now. The AIU is the new addition.

I’m 99% sure the cord was only plugged into the TIU IN port and not the AIU OUT.

Legion JD posted:

I’m 99% sure the cord was only plugged into the TIU IN port and not the AIU OUT.

What about the other 1%?

There are several threads on the forum that address backfeed from a TIU powering the TIU board enough to cause it to exhibit certain activity, but not enough to provide operations.   For example, when upgrading software or sound files, it sometimes becomes necessary to power down the TIU; if I recall a plugged-in WIU will keep it from shutting down.  I suggest you do a search.

I can assure you, from personal experience, that you wouldn't be the first person to make the stupid mistake of plugging into the wrong end of an AIU. 

I'd like the original poster to tell us more about the origin of his "new" AIU. Could it be new old stock? Remember some years ago there were AIU's sent out with bad cables that connect to the TIU. Maybe he has one? 


I checked with the seller and it was new, unopened, but older (5 years or so). I have a 6 conductor phone cable, but it’s longer than the original. 10ft vs 2ft stock cable. Would that work?


That 1% is probably gonna bite me..  ;-)    The only way to know is to buy another one, put a tape cover over the AIU OUT, and see if it works.

Yes, it can be fixed.  I sent mine in (how did you guess it was me?) to MTH and it was fixed at a reasonable price.  I no longer recall how much.  Of course, MTH is now closed due to virus.  I do not know if GGG can also fix an AIU, but you can ask him.

Legion JD posted:

... I have a 6 conductor phone cable, but it’s longer than the original. 10ft vs 2ft stock cable. Would that work?


10 ft is fine, but it must have the wiring order/orientation shown above explained in this OGR thread.


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gunrunnerjohn posted:

The AIU can be fixed.

why didn't I hear that message 2 months ago when I came here asking if anyone could look and fix mine?!  I got a lot of 'well, they never fail so no one knows how".

- walt

Hi guys,

Legion JD and Walt - I have the chips on hand to repair the AIU board.  I can make the repair for $50+shipping.

Legion JD - Don't give up on the AIU just yet.  There's another possibility you should check first.  As MTH told you, if a WIU is connected via the USB port on a Rev. L TIU, it will provide power to run the main processor.  However, it will not power the AIU's or even read the presence of the AIU's.  This makes the power up sequence VERY important.  If the WIU is on and you then bring up power on the Z-4000, the TIU won't read the presence of the AIU and you'll get the error message posted above.

Try the following...

1 - Disconnect the WIU/TIU USB cable.

2 - Power up the TIU via the Z-4000.

3 - Connect the USB cable.

4 - Power up the WIU and wait 1 full minute for the WIU to boot.

If the AIU is still functional, the TIU will now find it and the error message should go away.  If not, the AIU probably was damaged.

Thanks for the heads up Dave.  The authorized guy that I took it to gave up on it but a fellow forumite offered to sell me one, like new, for a really good price so I bought it.  If I ever decide to get the 'other' one fixed I'll remember your offer.

thanks - walt

Walt, you're touching upon a delicate area: the fact that having attended MTH school does not make a person a fully-qualified tech.

Quod natura not dat Salmantica non praestat


There are all levels of "graduates" from any school or training class.  To harbor the feeling that two or three days at a manufacturer's site makes you an expert in any field is pretty unrealistic.  You learn a lot of this stuff by doing, not by sitting for a couple of days listening to someone talk about it.  There really isn't any substitute for experience in almost any field of endeavor.

notice I didn't say WHY he gave up.  I was not in any way being critical of him in MY thinking.  He gave up because he couldn't get the chips.  Should I have said that?  I don't think it was necessary

Last edited by walt rapp

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