Network, generic

U0056 Vehicle Communication Bus D Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U0056 says Vehicle Communication Bus D works, but its traffic is disturbed. Bentley documents it for the Continental GT (2018-20), GTC (2019-20) and Flying Spur (2020): U005600 with symptom numbers 12689537, 12689541 or 12689542 lands in the chassis control unit (address 0074) or in roll control systems 1 and 2 (00D4, 00D5). Bus D is a private CAN there, and its errors pull in a series of suspension codes; the driver sees a red or yellow suspension lamp and a dynamic ride fault message. Bentley has technicians check the connectors and harness of the three units, then update the chassis control software, or replace the unit if it is on another software level. A production change came with a software update. Elsewhere, loose contacts or a resetting node are the usual causes.

Likely causes

Chassis control software level prone to Bus D errors (Bentley)
Loose or dirty connector at a module on Bus D
Damaged harness between the modules on Bus D
A module on Bus D restarting because of weak supply

Symptoms

  • Red or yellow suspension warning lamp (Bentley)
  • Dynamic ride fault message, several suspension codes stored
  • Functions drop out briefly and return

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,500
Time0.5–5 h

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

Parts involved

bus d wiringcontrol modulechassis control module

Related codes

U0029U0038U0047U0055U0065

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