DTC P1381: Misfire Detected - No EBCM/Pcm Serial Data: Description
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
This diagnostic will detect a loss of serial communication from the Electronic Brake Control Module (EBCM) to the control module. This serial communication is essential in order to distinguish misfire from a rough road condition.