P1381

P1381 is the sibling to P1380 — it sets when the PCM determines that the rough-road communication path is faulty (not just absent, but actively miscommunicating), typically because the message is arriving with a checksum error, a stale timestamp, or out-of-range values. This is a serial data bus integrity code, not a mechanical problem. Diagnose with a scan tool that can show bus traffic: monitor the EBCM's rough-road message at a 100 ms refresh rate while driving — the value should update smoothly and the message age should stay under 200 ms. If the message refresh is sporadic or the EBCM drops off the bus periodically, you have a bus-wiring issue or a failing EBCM. Check the GMLAN/Class 2 splice points (especially the body-side splice pack behind the IP on most GMT800/900 trucks) for green corrosion, and verify EBCM power and ground at the module connector with the engine running (battery voltage on the feed, less than 50 mV ground drop). The expensive misdiagnosis is replacing a PCM thinking it's a misfire-monitor calibration problem when the fault is a $0.50 splice clip that lost tension after 15 years.

Vehicle-specific patterns: 1999-2006 Silverado/Sierra 4.8L/5.3L/6.0L is the dominant P1381 platform — TSB 04-06-04-047 documents the EBCM-to-PCM rough-road suppression bug where the EBCM intermittently transmits a frozen Rough state, fooling the PCM and eventually setting P1381 as the freshness watchdog times out. 2002-2007 Trailblazer/Envoy 4.2L I6 sees P1381 from the IP harness rubbing through at the steering column bracket. 2005-2010 Cobalt 2.2L Ecotec throws P1381 when the BCM under the dash develops solder cracks at the Class 2 driver. 2007-2011 Silverado 5.3L AFM with cylinder deactivation occasionally sets P1381 alongside legitimate AFM-induced rough running. Estimated repair: $90 to $850.