U0073

U0073 means the CAN bus A controller has shut itself off, which is a self-protection mode triggered when a module detects bus errors exceeding its error-counter threshold (typically 255 frame errors per ISO 11898). This is a bus-level fault, not a module fault, and replacing modules first is exactly the wrong move. Cheapest-first: with the key off and battery disconnected, measure DLC pin 6 to pin 14: you must read 60 ohms. Reading 120 ohms means one terminator is missing (open wire, disconnected module, or failed internal terminator). Reading 40 ohms or less means an extra terminator or shorted module. Reading 0 ohms means CAN-H is shorted to CAN-L. Then disconnect modules one at a time (start with the most recently serviced or the most water-exposed: ABS, trailer module, aftermarket radio, aftermarket remote start) and re-measure. With the bus restored, key on, scope CAN-H and CAN-L: idle bus should sit at 2.5V on both legs, active bus should swing CAN-H to 3.5V and CAN-L to 1.5V in a mirrored pattern. Caveat: aftermarket installations (remote start, trailer brake controllers, dashcams hardwired to CAN) cause more U0073s than any single OEM defect, so always ask about recent installs before ordering parts.

Vehicle-specific patterns: 2008-2014 Dodge/Ram with TIPM-integrated gateway sets U0073 when the TIPM's internal CAN driver fails. 2003-2007 GM trucks with Class 2 and early GMLAN see U0073 from chafed bus wire at the body-to-frame harness behind the driver's seat. 2010-2015 Ford F-150 sees U0073 from aftermarket trailer brake controller back-feeding into the trailer-tow CAN spur. 2006-2012 BMW E90/E60 throws U0073-equivalent (BMW codes A0B1/A0B2) when the PT-CAN or K-CAN twisted pair gets damaged at the kick-panel splice. Estimated repair: $50 to $1400.