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- - Keys and ECU (https://www.ft86club.com/forums/showthread.php?t=100168)

Does anyone know if keys can only be programmed to one ECU at a time?
For example, if I had an ECU, and had the dealer security program the keys to a new ECU, will the old original ECU work if I decide to use that one instead?

Thanks

Im going to say no as you will need dealer to code ecu into security system and the keys are coded into imobiloser module

Man I just went thru this, the short answer is no.
The immobilizer is quite tricky on this car as it goes thru the body control module, combination meter, ECM and other modules. All of them must match and communicate with each other. If you lose your master you are sol and will have to buy a new BCM and Combo meter about 1600 bucks and then get it reprogramed.
Good news is you can down load Tech Stream delete the old codes first then reprogram, you can have up to 6 keys. Also I recommend downloading the service manuals and look under "replace ecm" depends what and how you do the swap there is a special way to reprogram AND remarry the ECM I think their are 6 different if not more ways depending on set circumstance.....IT SUCKS but it can be done if you take the time to read the manual......

some more info from manual

ECM
Customer must bring
at least 1 registered
key.
1. Replace ECM. *7
2. Register ECU
communication ID.
PROCEDURE
"G"

HINT:

A brief outline of ECU code registration procedure is shown above. For detailed information, refer to

the Techstream screen.

10. KEY REGISTRATION (PROCEDURE "G")

(a) ECU communication ID registration (When the main body ECU (network gateway ECU) is replaced

with a new one, or when the ECM is replaced with other than a new one.):

NOTICE:

The ECU communication ID should be registered when the main body ECU (network gateway ECU)

is replaced with a new one, or when the ECM is replaced with other than a new one, in order to

match the ECU communication IDs.

If registration of the main body ECU (network gateway ECU), combination meter assembly*1 or

transponder key ECU assembly*2 is not completed, then this work will not be possible. Therefore,

prior to carrying out ECU communications code registration, carry out main body ECU (network

gateway ECU), combination meter assembly*1 or transponder key ECU assembly*2 registration.

The engine cannot be started unless the ECU communication IDs match.

After registration, turning the ignition switch to START may not start the engine on the first try. If

so, turn the ignition switch to START again.

Using the Techstream, clear DTC B1572 (code for ECM immobiliser communication error) after the

engine is started.

*1: w/o Transponder Key ECU Assembly

*2: w/ Transponder Key ECU Assembly

HINT:

If both the main body ECU (network gateway ECU) and ECM have been replaced with new items at the

same time, then proceed as in "(b) When the ECM is replaced with a new one".

(1) Using SST, connect terminals 13 (TC) and 4 (CG) of the

DLC3.

SST: 09843-18040

Text in Illustration

*1 DLC3

(2) Turn the ignition switch to ON and leave the vehicle as is for 30 minutes.

HINT:

Do not start the engine.

(3) After leaving the vehicle as-is for at least 30 minutes, turn the ignition switch off and

disconnect terminals 13 (TC) and 4 (CG) of DLC3.

8/6/12 THEFT DETERRENT / KEYLESS ENTRY: ENGINE IMMOBILISER SYSTEM: REGISTRATION (2013 FR-S)

https:/

I'll definitely check out the service manuals more. Thanks for pointing me to that.

Could not following the procedure properly (for example not leaving the car for 30 minutes) cause codes like U0155 or U0073? My dealer is getting these DTCs even with a brand new ECU even though to my knowledge the instrument cluster works perfect.