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Welcome and thank you for allowing me to assist you! The 2002 and 2003 Liberty 3.7 engines both use a JTEC type PCM (engine computer) with 3 connectors. It was not until 2004 that they used the NGC type PCM with 4 connectors. You should be able to use your existing PCM with the 2003 engine. The only thing you may need to do is to swap the sensors and/or fuel injectors from your 2002 to the 2003 engine if the connectors at the sensors or injectors are different. Otherwise it should be a fairly easy swap.
I hope this information helps, and let me know if you need further assistance with this.
Yes that is correct.
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