2009 Rogue - New ECM, Vehicle Immobilizer Activated

[Dedpul]

Hello,

I had previously posted about my issues trying to get my car to pass a smog due to P0420 light sticking. I ordered an ECM as a sort of 'final test' and it finally came in. I got to work putting it in yesterday (Saturday, Nov 14) morning. I plugged in the new ECM, did relearn procedures, and car started up. Check engine light came on immediately with P0603 code, so I went to go put the original ECM back in. Now, the original ECM seems to have lost its key programming because the Vehicle Immobilizer activates when I put my keys in the ignition. I get a crank but no start due to the Immobilizer cutting fuel and spark. Any ideas why my keys wont work on the original ECM anymore but work fine on the new unit I got? Or are there special procedures I most likely didn't follow when replacing the ECM? I'm taking the car to the dealership come Monday to get one or both ECM's reprogrammed depending on what they tell me.

P.S. I spent all day Saturday swapping back and forth between ECM's because the new one gave me issues the second time I plugged it in (radiator fans blowing, no crank, all dash lights on). So many 'proper procedures' to learn when replacing things on these cars. I never had to get the keys programmed onto the new ECM, it came plug and play (for the most part)

[VStar650CL]

P0603 is just a low battery code, it can happen when your battery goes into "never never land" below 9V or from low-level sparks on a battery-disconnect. It probably didn't mean anything and would have erased after a key cycle. Here's the bulletin about it:

https://f01.justanswer.com/dcraig1000/1 ... 2c_eee.pdf

I have no idea why your car would even start with a new ECM without first reprogramming the keys. You should have got an immediate security light. The only thing I can think of is that some older models will allow you 7 starts with the lamp lit before they go into Lock Mode (P1610). It's likely that both of your ECM's are now locked and the car won't start until you program the keys. Because Nissan uses a rolling code for the IMMU, once the keys are programmed to a new ECM, the old one will no longer respond because the code is different. When replacing the ECM on any NATS vehicle, the steps after installation are as follows (in order):
1) Program all keys
2) Program the VIN number into the ECM
3) Perform IAVL (Idle Air Volume Learn)
4) Perform CTPL (Closed Throttle Position Learn)
Step 1 needs to be done every time you swap ECM's, even if the old one was already programmed to the car. The rolling code will change and the old ECM will throw a fresh set of security codes if it's reinstalled.