Network, generic

U0003 High Speed CAN Communication Bus (+) Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U0003 reports a break in the (+) wire of the high-speed CAN, which GM and FCA also call CAN-High. At rest this line idles near 2.5 V and is lifted about one volt for each dominant bit. Once it is cut, modules on the far side of the break lose the differential pair and drop out, while nodes on the intact section may keep talking. Standard high-speed transceivers cannot report a wire interruption on their own, as NXP points out, so whether a module stores U0003 depends on its own monitoring. Harley-Davidson lists U0003 together with U0001 as history codes in the ABS unit of 2017 Touring models when the TechLink interface was plugged in with the ignition already on; there no repair is due. Genuine breaks come from chafing, pushed-back terminals or corrosion.

Likely causes

CAN-High conductor broken at a flex point or after a repair
CAN-High terminal pushed back or corroded in a connector
Diagnostic interface connected with ignition on (history code only)

Symptoms

  • Modules beyond the break no longer reachable
  • Several warnings and fallback modes at once
  • Fault appears or disappears when the harness is moved

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–800
Time1–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

can high wiremodule connectorcan transceiver

Related codes

U0001U0004U0005U0006

References: static.nhtsa.gov, nxp.com, saabwisonline.com.