Network, generic

U0009 High Speed CAN Communication Bus (-) Shorted to Bus (+)

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U0009 describes CAN-Low and CAN-High of the high-speed bus being shorted to each other. The voltage difference between them then stays at zero, which every receiver interprets as recessive, so a dominant bit can never form; onsemi's tests show transmission stopping entirely and controllers running into bus-off. According to NXP, transceiver bus diagnosis cannot detect this short, so a module infers it from protocol errors instead. No manufacturer documents U0009 publicly. With the battery disconnected, the resistance between both lines reads close to zero ohms instead of the usual 60. Likely sources are a crushed harness section, water inside a splice or connector, or a damaged transceiver in one module bridging its two bus pins. Unplugging modules one by one narrows the location down.

Likely causes

Bus pair crushed so that both conductors touch
Water or corrosion bridging CAN-High and CAN-Low in a splice or connector
Failed transceiver shorting both bus pins inside a module

Symptoms

  • No communication on the high-speed network at all
  • Numerous warnings, fallback modes, possibly no start
  • Scan tool reaches only modules on other networks

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,200
Time1–6 h

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

Parts involved

can high wirecan low wiremodule connector

Related codes

U0001U0002U0004U0008U0018

References: onsemi.com, nxp.com, ti.com.