2005 Nissan Xterra P0420 and U1000 Fault: 10A ECM Fuse Blows When Power Off

Model: 2005 Nissan Xterra Fault Code: P0420 Posted: 2018-05-17 17:13

I own a 2005 Nissan Xterra with the 4.0L engine. The vehicle is showing OBD-II diagnostic codes P0420 (Catalyst System Efficiency Below Threshold) and U1000 (ECM Communication Failure). When I turn off the car, a 10-amp fuse for the Engine Control Module (ECM) blows consistently. After replacing the fuse, the vehicle cranks but runs very sluggishly with poor acceleration—this strongly indicates a clogged catalytic converter. However, I'm unable to determine why the 10A ECM fuse is blowing every time the engine is turned off. The issue appears to be related to both the catalyst efficiency and communication between the ECM and other systems. Can anyone explain this behavior or suggest troubleshooting steps for the P0420 and U1000 codes in a 2005 Xterra?