Network, generic

U0045 Vehicle Communication Bus B (-) Shorted to Bus B (+)

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U0045 describes the two wires of Vehicle Communication Bus B touching each other. Deutz uses this code in the EMR L1 engine controller for a short circuit on its third CAN channel, without further detail. On a high-speed-type CAN, bridged wires leave no differential voltage, every bit reads recessive and, per onsemi, nothing can be transmitted while the CANH driver works into its current limit; NXP adds that transceiver diagnosis cannot see this short. On a fault-tolerant low-speed network, NXP's TJA1055 first sees a permanent dominant level, then after a time-out switches off CAN-Low and keeps going on CAN-High. Typical causes are crushed harness sections, water in splices and a damaged module input. No car maker documents U0045 publicly; near-zero ohms between the wires with the battery off confirms the fault.

Likely causes

Harness crushed so that both bus wires touch
Water in a splice or connector bridging the two wires
Damaged module input shorting its bus pins

Symptoms

  • Every function on Bus B unavailable (high-speed type)
  • Several warning lamps on at once
  • Lost-communication codes in modules on other networks

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,000
Time1–6 h

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

Parts involved

bus b wiring

Related codes

U0036U0037U0040U0044U0054

References: serdia.deutz.com, serdia.deutz.com, onsemi.com, nxp.com.