DTC U1001-U1254: Loss Of XXX Communications: Description

Modules connected along Class 2 serial data line monitor serial data communications during normal vehicle operation. Operating information and commands are exchanged between modules and operating systems. When a module receives a State Of Health (SOH) message from another system, that module records identification number of system which sent SOH message. If SOH is not received, receiving module must use a default value for non-transmitting module. Once an identification number is learned by a module, it will monitor that system for its unique SOH message. Each system on Class 2 serial data line must send a SOH message every two seconds. When no message is detected from any system for 5 seconds, DTC U1XXX (XXX is equal to a three digit identification number) will store. See DIAGNOSTIC TROUBLE CODE IDENTIFICATION NUMBER  table to determine which system is not communicating. For example, if DTC U1016 is stored, Powertrain Control Module (PCM) is not communicating. A current DTC clears when malfunction no longer exists. A history DTC clears when module ignition cycle counter reaches reset threshold without a repeat of malfunction.