2003 jeep liberty 3.7 po605 code what could be the problem

This trouble code basically means that the PCM/ECM (powertrain/engine control module) has detected an internal control module fault in the ROM (read only memory) in the PCM. The PCM is basically the vehicle's "electronic brain" that controls functions such as fuel injection, ignition, etc. When self-checks fail in the ROM, this DTC (diagnostic trouble code) is set.

There is an internal fault in the PCM / ECM

Using an aftermarket performance programmer may trigger this code

In some cases, "flashing" the PCM with an updated software can fix this DTC. You will need access to make & model specific information such as Technical Service Bulletins (TSBs).
If there are no PCM flash updates, the next step would be to check some wiring. Inspect and check for proper voltage and ground to the PCM and throughout the associated circuits. If there are problems with them, repair and retest.
If the wiring checks out OK, the next step is to replace the PCM, which is the most likely repair for this code. This is generally not a "do-it-yourself" task, although in some cases it may be. We strongly recommend you have a qualified repair shop / technician do the work, one that has the capability to reprogram the new PCM. Installing the new PCM may involve using special tools to program the vehicle's VIN (vehicle identification number) and/or anti-theft information (PATS, etc.).
In some cases, "flashing" the PCM with an updated software can fix this DTC. You will need acess to make & model specific information such as Technical Service Bulletins (TSBs).
If there are no PCM flash updates, the next step would be to check some wiring. Inspect and check for proper voltage and ground to the PCM and throughout the associated circuits. If there are problems with them, repair and retest.
If the wiring checks out OK, the next step is to replace the PCM, which is the most likely repair for this code. This is generally not a "do-it-yourself" task, although in some cases it may be. We strongly recommend you have a qualified repair shop / technician do the work, one that has the capability to reprogram the new PCM. Installing the new PCM may involve using special tools to program the vehicle's VIN (vehicle identification number) and/or anti-theft information (PATS, etc.).

An internal computer problem. Read only memory. This is the factory defaults. These can't be erased by a tech. But can be by a system fault. You can get the computer online for about $160. Plug and play. Dealers 2 to 3 times this.