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Hello,

I am working on a 2003 Civic for a friend trying to figure out why you have to relearn the keys Everytime the battery power is disconnected for more than like 10 seconds or when the battery dies.

​​​​​​I can relearn the keys with my scan tool and get the immobilizer light to go out. After that, the car starts and runs fine.

When I try to relearn the keys it initially fails then I have to do the replace ecm function in my scan tool and then the light goes out.

I tried replacing the immobilizer unit with another one thinking that there was a problem with memory retention once the power is gone. When I replaced the immobilizer unit I then get an error when trying to register the new immobilizer that says to try registering the MICU.

Everytime I try to register the MICU the procedure fails.
Tried replacing the MICU with one I got at a junkyard and no change. The registration process still fails.

I don't think it is a battery issue because when the keys are in the immobilizer unit it works just fine when the car is stuf off with the key. The problem only happens when the battery dies or is disconnected.

Haven't checked the communication wires but I also wouldn't think those would be an issue because I don't have any communication codes and the key relearn process completes with the old immobilizer unit.

WHen I connect to the immobilizer I get a imm code type 05 message.

I also noticed that the key type in the immobilizer info goes from a type 1 key on the old immobilizer unit to a type 2 key on the new immobilizer unit. I am not sure if than has anything to do with it.

I am using a launch x431 scan tool.

Any help or insights would be appreciated. Thanks.