Network, generic

U009B Vehicle Communication Bus I

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U009B addresses Vehicle Communication Bus I overall, the ninth network letter. Which network sits behind I is left to the manufacturer and not named in any public bulletin; U009B itself is not documented publicly by any maker. CARB requires that a lost digital input be detected with a separate code, which is the role of this group. Bus I has no wire-level codes of its own in the list, so U009B must also cover line faults. One cause is easy to overlook: a single module with a fault in its controller can hold the bus dominant. NXP's TJA1042 and TJA1051 transceivers counter this with a time-out that switches off the transmitter, so that the remaining nodes keep talking. Unplugging modules one by one finds such a node.

Likely causes

Open or shorted wire on Bus I
One module holding the bus dominant
Missing supply or ground at a Bus I module

Symptoms

  • Functions of Bus I modules fail or act erratically
  • Lost-communication codes in several modules

Repair estimate

DifficultyHardWorkshop job
Parts and labour€50–900
Time0.5–5 h

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

Parts involved

bus i wiringbus i nodes

Related codes

U007BU0092U009CU009D

References: law.cornell.edu, nxp.com, en.wikipedia.org.