Im swapping the ecm putting a used one same numbers i need to re-flash the immobilizer to use the original key so the car will start

go have a key cut using vin and use original pcm if you swapped out the ignition already then need to have all components programmed/flashed to the vehicle/ vin

The Immobilizer needs to be reset to the vehicle so the ECM and BCM recognize it.

https://www.google.com/search?q=2006+honda+odyssey+reset+immobilizer

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THE ECM NEEDS TO BE PROGRAMMED FOR YOUR CAR

It shouldn't unless you are taking the engines computer for the new one if so yes you do and the instrument cluster and thise keys also these are programmed together and if the computer doesn't see the matching signal you will be in theft mode if it's just the same size engine then no you don't the pats or secure lok system matches the key chip that's programmed into the computer with the instrument cluster then it goes into the immobilizer then the signal from it goes to the ecm/computer to tell it that it's ok to start so that's how it is in the USA AND I'M SURE YOURS WORKS THE SAME WAY ( SO JUST THE SAME SIZE MOTOR THAT THE ECM CAN MANAGE THE SENSORS /////NO YOU DON'T NEED IT\\\\\ DIFFERENT SIZE ENGINE YES YOU DO NEED EVERYTHING INCLUDING THE KEYS ,IMMOBILIZER ,INSTRUMENT CLUSTER ,ECM ( COMPUTER)

TATA Indica Vista ECM / ECU - YouTube

? 2:26
https://www.youtube.com/watch?v=rRk5zSFA1eg
Mar 8, 2014 - Uploaded by Flip Keys
This video shows how to open TATA Indica Vista and ManzaECM / ECU for repair purpose.

How to extract Immobiliser Chip from Indica Vista key ...

? 0:52
https://www.youtube.com/watch?v=pqG0T99Xce0
Nov 8, 2012 - Uploaded by Flip Keys
If your original Indica Vista key breaks, wears-out or gets damaged then you can re-use its immobilizer chip ...

Maruti Suzuki SX4 ECM / ECU - YouTube

? 2:37
https://www.youtube.com/watch?v=pWjmh1QUhHQ
Jan 12, 2014 - Uploaded by Flip Keys
If you are repairing Maruti Suzuki SX4 ECM / ECU or coding a new immobilizer key then you can open the ...

TATA Motors INDICA VISTA Owner's Manual - ManualsLib

put back old ecm and try spare key. if it does not work and you use a new ecm you need to program your keys to the immobilizer for it to work

Put key in ignition.
Press unlock button on key fob.
Immobilizer should now recognize it, if it was original fob but car or fob battery was changed or is now low.

Saabs are particular about batteries that are otherwise good, but just below 12 volts.

immobilizer light light flashing means your ignition key transponder worn or faulty ignition switch lock cylinder antenna ring. read keys.the immobilizer control module faulty or ECM.NEED HAVE VECHICLE CODE SCAN SEE WHAT FAULT CODE YOU ARE GETTING.

MAKE SURE YOU USING THE RIGHT KEYS. TRY ANOTHER IGNITION KEY.PLACE KEY IN THE SWITCH. TURN IGNITION SWITCH TO ON POSITION UNTIL IMMOBILIZER WARNING LAMP ILLUMINATES FOR 2 TO 3 SECONDS. IF IMMOBILIZER WARNING LAMP ILLUMINATES FOR 2 TO 3 SECONDS THEN FLASHES RAPIDLY.KEY CODE NOT RECOGNIZED.REMOVE KEY AND TRY AGAIN. IF ALL FAILS TAKE CAR TO DEALERSHIP THEY HAVE TO USE DIAGNOSTIC EQUIPMENT TO FIX CAR.PROBLEM COULD BE IN THE IGNITION SWITCH,BCM,FAULT IN THE ECM OR IMMOBILIZER CODE INCORRECT.

When the ignition switch is turned on, the immobilizer control module sends a challenge signal through the antenna around the ignition switch to the transponder chip in the ignition key. The transponder key responds with an encrypted key code. The immobilizer module then decodes the key code and compares it to the list of registered keys. When the engine is started, the ECM sends a request to the immobilizer module over the data bus to verify the key is correct. If an attempt is made to start the vehicle with an invalid ignition key, the immobilizer module sends a message over the data bus to the instrument cluster to flash the anti-theft indicator lamp. If the ECM does not receive a "valid key" message from the immobilizer module within 2 seconds of engine start up, the ECM will disable the fuel injectors to kill the engine. You'll need to get a new key and get it registered in the immobilizer control module. You'll need a scan tool, the VIN number, the date manufactured and a factory-assigned PIN number.