The customer must acknowledge that if they are providing a replacement ECU/PCM, it has to be a suitable replacement. This means that it has to be the same exact part number or interchangeable. There are many vehicles where just one letter or number off can mean it's entirely different inside.
From the original, we clone over the software which includes the VIN, immobilizer, and calibration specifically for any given vehicle.
If the original is beyond reading because it's physically fried or has an internal failure preventing us from reading the original, the servicing tech makes an internal call regarding our options. Either we repair the original enough to get it reading or we do what's called an IMMO-OFF on the replacement.
IMMO-OFF is when we disable the security on the ECU/PCM altogether so the vehicle won't be prevented from starting because of the ECU/PCM. This rarely happens and only in a handful of cases does it happen. On most units, we can read the original.
Steps to make this a successful cloning service:
Step 1 - We must know if anything else besides the ECU/PCM was replaced. Many customers might not be aware that depending on the YMM (year, make, model) the immobilizer (security feature that allows the car to start) is usually stored in multiple places.
For ex. Instrument Cluster, BCM, ECU/PCM, and sometimes another module. Most modules are VIN/Immobilizer encoded. The newer it is, the more units are VIN/Immo encoded. If everything is original besides the replacement ECU/PCM that we cloned, move on to the next step.
Step 2 - Scan the vehicle with an OBDII scan tool in order to provide codes for the ECU/PCM. Based on those codes we'll be able to see on our end what module is still preventing the vehicle from starting.
On a good OBDII scan tool, you will be able to see the VIN stored on the ECU/PCM, and on the replacement, the original VIN should be showing up.
Step 3 - Perform a hard battery reset to re-sync all of the computer modules and clear any codes with an OBDII scan tool after knowing what those codes are.
If those 3 steps were taken into consideration and it points to the replacement ECU/PCM still being at fault due to a VIN/Immo mismatch, we can take another look under warranty.
Lastly, many vehicles have VIN/Immo encoded key fobs and a physical IMMO box right behind the ignition as well where the key fob is inserted. If a key fob battery is dead, the transponder inside that key might not be giving the correct signal preventing the vehicle from starting.
It's worth trying another key (if you have one) to make sure the battery inside the key fob is good.