P1380

P1380 means the PCM's misfire monitor cannot access rough-road data from the ABS/EBCM module over the GMLAN or Class 2 serial data bus, so it cannot suppress false misfire detections caused by wheel-speed jitter on broken pavement. The misfire monitor still runs, but without rough-road compensation it will throw false P0300/P030x codes whenever the truck hits a frost heave or washboard surface. Diagnose by first checking for ABS/EBCM communication codes — if the EBCM is offline (U-codes pointing to U0121 or similar), fix the bus problem first because P1380 is the symptom, not the cause. With a scan tool, verify rough-road data is being broadcast: the EBCM should publish a rough-road status PID that toggles between Smooth and Rough as you drive across rumble strips at 30 mph. If the EBCM is awake and the rest of the network is healthy, suspect a calibration mismatch — a flashed PCM or EBCM from a salvage yard with a non-matching part number will set P1380. The expensive misdiagnosis is chasing misfire ghosts on a truck that runs fine — recognize P1380 as a communications/calibration code, not an ignition problem.

Vehicle-specific patterns: 1999-2007 Silverado/Sierra/Tahoe/Yukon/Suburban 4.8L/5.3L/6.0L sets P1380 most commonly when the EBCM module is replaced with a unit from a different RPO or model year — the message structure doesn't match. 2003-2007 Trailblazer/Envoy 4.2L I6 sees P1380 from the EBCM wakeup circuit failing intermittently. 2004-2008 Colorado/Canyon 2.8L/3.5L/3.7L throws P1380 after wheel-speed-sensor harness damage, which knocks the EBCM offline. 2005-2009 Equinox/Torrent 3.4L sets P1380 from a corroded under-seat body-control connector that carries the Class 2 bus segment. Estimated repair: $120 to $700.