For others reading, if you have one smart key left you should get additional ones paired asap. Typically only one of the keys (the master) supplied from the factory is able to program new fobs, so that key may eventually be lost. Only a Toyota dealer is able to override this policy if there's no master key.

I don't have an EWD for Gen 3.5 (2010-2012) but this system is probably the same as in this 2006 EWD. The smart key ECU is behind the glovebox, so replacing that is certainly DIY-able.

Spoiler: Passenger Side Diagram

@inov8 can probably comment as to the exact location & procedure to replace the immobilizer code ECU, but to me it looks like it's accessible if you remove the left wood trim, ignition trim panel, radio/vent trim panel, and then the gauge cluster.

Spoiler: Driver Side Diagram

In my opinion, you should start with the smart key ECU. That would be the most likely cause of a no-pair situation. It's possible the ECUs are paired together but let's hope that's not the case. inov8 probably knows.

 

Thanks michaelproeber! Hope to hear from @inov8 .

 

Toyota dealers like to apply their own terms to describe parts. This helps to dissuade potential customers from performing independent research in hope of finding a more cost-effective solution. Attached are two figures copied from the Toyota Avalon Technician Training Manual, Smartkey system chapter. The left figure is a list of all the components and what each is supposed to do. The right figure shows the approximate location of each.

Note there is no part called either a "Transponder Computer Assembly" or "Immobilizer", so it is difficult to confirm or refute the claim that the suspect component is located "deep behind the firewall", and not just behind an easy-to-remove instrument panel section.

Incidentally, I think perhaps the "9990-41082" part number should be "89990-41082".

 

Thanks inov8!!! The dealer did refer to the parts needing replacement as the Certification ECU and ID Code Box (their print-out paperwork is listed below). You are correct about the part # being 89990-41082 as I misspelled it in the first post. I found a same year car that is being parted-out in town and they will sell me the Cert ECU for $75.00. There is another shop in town who can reset (virginize it) for under $100. Thoughts on first trying to replace the Cert ECU before paying the dealer to tear the dash out to replace the ID Code Box? I asked Grok3 (AI) what the chances of both having a failed Cert ECU and ID Code Box and the reply was 60%-70% chance that the Cert ECU is more likely to fail than the ID Code Box. I'm wondering why the dealer would want to change out both with all that labor to get to the ID Code Box when they could just suggest by starting with the ECU Cert. Any further direction or thoughts are appreciated!

 

I do not see any risk (other than the ~$200 expense) in replacing just the more accessible part and hoping for the best. The worst that can happen is your Avalon will then be similar to one where just the ID Code Box is defective. You could then reinstall the original part and resell the "new used" one to recover some of your cost.

I found this short You Tube video that supports the dealers accessibility claim. My guess is Toyota mounted it there as a deterrent to car thieves with flat bed tow rigs. Little did they realize that, in this country, selling off the parts is more financially rewarding and less risky than selling a complete stolen vehicle.

 

After some further wiring diagrams research, I discovered the ID Code Box/Module (aka: Immobilizer ECU) has an 8 terminal connector, of which only 5 are actually used . . .

• Battery ~12V
• Ground
• Local digital network
• 2 wires that connect only to the Engine Control ECU

All of these wires terminate at connectors located just behind or above the glove box. This suggests, should you need to replace it, there exists a practical alternative to disassembling the entire instrument panel (which also involves evacuating the air conditioner and draining the cooling system).

(a) Locate the 5 wires and cut them, thereby isolating the defective ID Code module;
(b) splice 5 new wires to the connector side of the aforementioned cuts;
(c) purchase (at a salvage yard) a used ID Code module connector with a length of the harness attached;
(d) connect the spliced wires to the salvage connector, plug it in, and mount the replacement ID Code module in some convenient location.

 

Wow... Your good inov8! In the video you sent it appears the 8 wire terminal connector has each wire color coded a different color? I would then try to find these colored wires behind or above the glove box where they terminate and splice in the new/used harness so I can attach the relocated immobilizer near the glove?

 

I now have the car at an electrical mechanic's shop who is know for being an ECU Wizard. He assured me that if he can't fix, I don't pay him anything. I figured this is a worthwhile effort in order to avoid replacing the Smart Key ECU and ID Code Box by tearing the dash apart. He has had the car for four days now and I checked in to see how progress was going in which he informed me that he has had no luck thus far and his next step is to reprogram the Smart Key ECU. He additionally states in order to do this he must get access to the ECU which is located in the trunk area of the car. Does this location sound correct for a Smart Key ECU or anything ECU related? AI generated the below response. Looking for anyone else's thoughts or experience. THANKS!

The trunk is a logical location for the Smart Key ECU or related hardware because:

• It houses the antenna for the trunk release function, which needs to detect the key fob’s signal.
• It’s a secure, protected area less exposed to engine heat or front-end collisions.
• Wiring for rear systems (e.g., trunk release, rear lights) is already routed through the trunk, making it a convenient spot for related modules.

 

The 2011 Avalon wiring diagram shows the following modules as components of the push-button start ("immobilizer") system:

D44 Power Source Control ECU
D21 Power switch (push button)
D14 Steering Lock ECU
D29 ID Code Box
D38 Certification ECU
A55 Engine Control Module

Note that the term "Smart Key ECU" was not used for model year 2011, though it was in earlier years, so I am not sure which part he is referring to. It might be D38 or D44.

The drawing attached to Post #4 shows the locations of the listed modules.
The Engine Control Module ("ECM") in 2011 is located under the hood on the passenger side.
My 2005 Avalon factory service literature shows the Smart Key ECU to be located behind the glove box.

 

Thanks inov8 . I have requested the Cert ECU to be pulled from a few recyclers who have the same year Avalon. I two separate instances they said they spent hours looking behind the glove compartment but could not find it. I'm guessing like the Id Code Box the dash has to come off (big job) in order to access the Cert ECU? Thanks!!

 

Perhaps the recyclers are searching in non-smartkey models, or not sure what the module looks like.
Attached drawings are from Toyota 2011 service literature. D39 is the Certification ECU.

 

Additional drawings. Note that Certification ECU only exists in models with Smartkey.

 

Finally managed to find some detailed Certification ECU removal instructions . . .