When someone says their Subaru is immobilized or has an immobilizer it means there is a secondary security module that without the proper inputs keeps the car from starting, or if it does start, it dies immediately. Unlike conventional aftermarket security systems that use a starter interrupt to keep the car from cranking over, the Subaru immobilizer system uses a combination of fuel and ignition cut-off so it can't be defeated. Most car brands have some type of immobilizer or chipped key for security purposes. Below we talk about how an immobilized car can effect your Subaru swap.
Earlier immobilized models need the matching key, immobilizer box, and ECU from the same car to make the car start. For CANBUS equipped cars it requires the gauge cluster, key, immobilizer box/body integrated unit (all-in-one module) and ECU from the same car.
For all immobilized swaps it's important to have the ignition cylinder because the ring around the key (that also lights up when a door opens) is the antenna to pick up the RFID chip from the key. The placement is very precise so even if you hide the key under the dash you'll want to use the ignition cylinder to hold the key in place or it's liable to move and cause the car not to start. Our recommendation is to utilize the chipped key with ignition cylinder on whichever steering column is installed in the car. This is because it keeps the benefits of the immobilizer system intact since the key will go with the driver and the keyless entry will still work as it did before. If having two different keys is an issue it's possible to swap the lock cylinders in the door to match the chipped key.
2004 STI and 2004 Forester XT use the same basic setup as 05+ Forester and 04-06 STi models but are non immobilized ECUs so switching to a non immobilized ECU could be an option. Just keep in mind the non immobilized ECUs are tough to find anymore.
No matter what, if the ECU is from an immobilized car it will need its paired items or the car will not start. If the engine is purchased separately or is missing one of the immobilizer components the best thing to do is find another already paired set. They can be found on eBay or iWire can supply them depending on the situation.
Which cars are immobilized?
2004 and Older Legacy
2004 and Older Forester
2004 and Older STi
2005 and Older WRX