Network, generic

U009A Vehicle Communication Bus H (-) Shorted to Bus H (+)

Check engine lightUsually off

EmissionsNot relevant

Drive cycleNot required

Limp modePossible

U009A means the two wires of Vehicle Communication Bus H touch each other, on a CAN CAN-Low against CAN-High. No manufacturer documentation of U009A is public. On a high-speed CAN this ends all traffic; onsemi's bench node could not send and drew about 47 mA against roughly 65 mA on a healthy bus. A fault-tolerant low-speed CAN can live with it: the TJA1055 from NXP initially reads the bus as constantly dominant, and only once a time-out has run does it disable its CANL driver and carry on single-wire, returning to differential operation once the wires are separated. So on some cars U009A comes with a dead network, on others only with a stored code. Separating harness sections while measuring resistance between the wires narrows down the spot.

Likely causes

Bus wires crushed together

Wet or corroded splice joining both wires

Internal short in a module's transceiver

Symptoms

On high-speed CAN: complete loss of Bus H functions
Lost-communication codes for several modules

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 h wiringmodule connector

Related codes

U007A U0091 U0094 U0097

References: onsemi.com, nxp.com, law.cornell.edu.