Network, generic

U0081 Vehicle Communication Bus F Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U0081 marks Vehicle Communication Bus F as working but unreliable: frames arrive damaged, late or not at all from time to time, while the network as a whole stays up. No manufacturer documents U0081 publicly. Jaguar Land Rover shows how close the boundary is by recording invalid serial data on Bus F as failure type 81 of U0080 instead. Where Bus F is FlexRay, as on Audi's A6/A7 link to the transmission, each transceiver can check its own output: NXP's TJA1081B raises a bus error flag whenever the level it reads back on the BP/BM pair disagrees with the data it is sending, which happens with collisions, interference or a damaged pair. CARB asks for communication errors on digital signals to be detected, not only total loss. Intermittent contacts and moisture are the usual culprits.

Likely causes

Loose or corroded contact in a Bus F connector
Twisted pair of Bus F damaged or untwisted near a repair
Electrical interference from an aftermarket device
Module software that handles bus timing incorrectly

Symptoms

  • Functions on Bus F drop out briefly and return
  • Several modules store communication codes at the same time

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–900
Time0.5–5 h

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

Parts involved

bus f wiringmodule connectorcontrol module

Related codes

U0065U0078U0080U008A

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