Immobilized ecu dead key fob

I think you are dealing with mechanics who are not very good. I believe a pre-existing fob usually can not be reprogrammed from scratch but a new one can if you still have another good one. Otherwise they wipe everything and start with new fobs. I am going by what I have read in the past, not personal experience.

It could be the locksmith fouled up the sequence and then had to sell you a new fob. Its not clear what you meant by "they couldn’t program my old key my new used cleared key." Old, new or used cleared fob?

You could check The Care Care Nut youtube channel. He has a recent video about programming fobs.

 

It's not an ecu problem. It's and "OE". Operator Error.
Apparently they don't know how to program a key.
I hope you had them reinstall the original ECU and refund your money.
They told you that would solve the problem, and it didn't.

 

Wow. What a mess. I think the mistake was the assumptions made after the dual battery diagnosis followed by parking it.

At that point the high voltage battery was still functional. All the car really needed was the 12v battery. The hv battery can't be totally dead and still allow the car to run from the dealer to your house.

However the hv battery could have been weak in a ten year old car.

From that point on its hard to say what happened. I would revisit the diy hv battery swap, a significant job that could have a missing step, cable, nut or even an orange plug not completely pushed in, a three step process often responsible for a no start. I would verify the new 12v installation and voltage. Most likely many 12v jump starts have occurred, I would check the 125a fuse in the engine fuse box which instantly blows on a reverse polarity jump.

The keyfob was ok when you parked it, I suspect its failure was a guess or perhaps a misdirection because the car would not go Ready. Its possible the locksmith or subsequent dealer attempts on this cleared the existing fob registrations. To add confusion, in your first post you said the locksmith started the car, in the second he failed?

At this point there have been so many hands on the battery and control systems that multiple problems can exist, a situation "good" mechanics have trouble with. You need to find an expert diagnostician on a Prius. I would expect a dealer would be the place, maybe not in your case based on the "full" story.

 

Did you ever get the car fixed Im having the same kind of issue?

 

you need new batteries and ecu's? might as well total it

 

When you power up the car do you try to start it with the brake pedal pressed first try?

When you replaced bad batteries, you need to push the start button twice without pressing the brake pedal.

The system needs to recalibrate the ecu's
Once that is done then power down and then try starting it normally with brake pedal pressed.

 

My problem started with a six-year-old 12-volt battery that was nearly dead. While the battery voltage was extremely low, the unlock buttons were pressed and several attempts were made to start the car. The battery did not have enough power to complete the unlocking or startup process properly. After multiple failed attempts, the vehicle entered what appears to be a security-lockdown state.

Now, none of the keys work—including the original key that previously operated the vehicle.

Based on this experience, I strongly recommend that owners of vehicles equipped with smart-key systems avoid repeatedly pressing the lock or unlock buttons or attempting to start the vehicle when the 12-volt battery is severely discharged. First, connect a reliable 12-volt power source or install a fully charged battery producing approximately 12.7 volts.

In my case, replacing the old battery did not restore the system because the security lockout had already occurred. The car is now stuck in a security-blocked condition that even the dealership has been unable to diagnose or correct

Pressing the brake pedal, pushing the power button twice, cycling the door-courtesy switch, and flashing the headlights have all failed to wake the immobilizer system.

You cannot simply replace the immobilizer ID code box without matching it to the certification ECU. Likewise, you cannot replace the certification ECU without registering it to the immobilizer system.

Here is my understanding of how the system works:

When you approach the Prius, the exterior antennas transmit a low-frequency 134 kHz signal that activates the key fob. The certification ECU receives and verifies the key’s response using the information stored in its memory. It then confirms the authorization information with the ID code box, also known as the immobilizer ECU. If everything matches, the system activates the door oscillators and allows the doors to unlock.

The certification ECU then remains awake and waits for the next step. The interior oscillators determine whether the key is inside the vehicle. The certification ECU verifies the key again and confirms authorization with the ID code box. If the required conditions are satisfied—such as the vehicle being in Park, the brake pedal being depressed, and the hybrid system passing its safety checks—the certification ECU authorizes the vehicle to enter READY mode.

My Prius appears to be stuck in a security lockout, or “brick,” condition. The certification ECU and immobilizer ID code box must contain matching registration information. Replacing only one of these components without synchronizing it to the other leaves the security barrier in place and prevents the vehicle from starting.

Toyota Techstream can normally perform an immobilizer reset or an all-keys-lost procedure, provided that a new, unregistered key is available. However, the dealership could not perform the procedure because the relevant body and smart-key ECUs would not wake up or communicate.

When Techstream is connected through the OBD-II port, it can communicate with the engine ECU, hybrid-control ECU, and combination-meter ECU, but it cannot communicate with the body ECUs involved in the smart-key system. This includes the certification ECU and immobilizer ID code box. Because those ECUs remain offline, they do not appear as accessible or serviceable systems in Techstream.

Advanced locksmith equipment, such as certain Autel systems, may be capable of forcing communication with these ECUs by controlling the necessary wake-up and communication circuits at the proper time. That is where I am currently stuck.

I am not willing to spend $3,000–$4,000 on an Autel system because the car is not worth that investment. I already have a working Techstream setup and a compatible cable, but I have not found a practical way to wake the certification ECU and immobilizer ID code box so Techstream can access them and perform the all-keys-lost reset.

I also had a mobile key programmer attempt to make a key. Unfortunately, many mobile technicians are unfamiliar with what is required when all keys are lost and the smart-key ECUs are not communicating.

The dealership appears to be treating this as a conventional electrical or component failure. As a result, they may continue replacing parts and troubleshooting individual circuits without recognizing the central issue: the smart-key and immobilizer ECUs are not waking up, so Techstream cannot access them to complete the required security registration.

 

There is no security lockout.

It is possible the immobilizer ecu is bricked. The dealer would be able to tell you this using the newer GTS+ Techstream.

The older "mini-vci" Techstream version everyone uses no longer can reset immobilizers and start fresh with new fobs. In fact it could never do it without being a "Security Professional" and being online to receive a seed code using a full access subscription from Toyota.

In the past some overseas sellers would sell seed codes illegally but that no longer works.

Toyota disabled the old Techstream online functions once their new GTS+ graphical version was released. You can download it with a subscription but the advanced "Security Professional" subscription is only available to nationally certified locksmiths and dealers.

You could call this locked down but it is a security function to make the cars harder to steal, especially 2022 and newer when the rf fobs were revised.


Some locksmiths now have Techstream GTS+ and could do an immobilizer reset assuming the immobilizer is not actually bricked. New unused keyfobs are then programmed.

If the dealer indicated the immobilizer ecu was bricked, it is a dash out, ac system out procedure because the immobilizer is behind those assemblies. However a bricked immobilizer ecu is extremely rare.

Two simple steps
The second works without a fob battery