Network, generic

U0091 Vehicle Communication Bus G (-) Shorted to Bus G (+)

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U0091 closes the Bus G block: the (-) and (+) wires of Vehicle Communication Bus G are joined, on a CAN CAN-Low to CAN-High. No manufacturer has published a use of U0091. With both wires bridged no voltage difference can form, so a high-speed CAN carries no frames at all. Transceiver self-diagnosis is of little help here; NXP notes that its TJA1043 reports shorts to ground and supply but not a short between the two bus wires, so the module concludes the fault from the silence. Measuring is quick: Nissan gives about 60 ohms between the wires as normal and lists zero ohms for a short between them. To find the spot, unplug modules and harness sections one at a time until the reading returns to normal.

Likely causes

Bus wires crushed together, e.g. under a seat rail or panel
Corroded or wet splice bridging both wires
Internal short in one module's transceiver

Symptoms

  • Complete loss of the functions served by Bus G
  • Scan tool cannot reach any module on Bus G

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 g wiringmodule connector

Related codes

U0079U0088U008FU0090U009A

References: nxp.com, static.nhtsa.gov, law.cornell.edu.