Network, generic

U0049 Vehicle Communication Bus C (+) Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U0049 reports the (+) wire of Vehicle Communication Bus C shorted to ground. If Bus C is a high-speed-type CAN, the affected conductor is CAN-High; for a dominant bit it should climb to roughly 3.6 V, which a grounded line cannot do, and onsemi's tests show the node unable to send anything while its CANH output works into a current limit of up to about 120 mA. Every module on Bus C drops out at the same moment, and members of other networks begin logging missing messages. The fault-tolerant low-speed variant reacts more gracefully, since NXP's TJA1055 counts a grounded CAN-High among the failures that leave ongoing traffic intact. No manufacturer documents U0049 publicly. With the battery disconnected, CAN-High at a few ohms or less to ground confirms the short.

Likely causes

(+) wire of Bus C chafed through to ground
Harness pinched during assembly or repair
Shorted transceiver in a module on Bus C

Symptoms

  • All functions on Bus C fail together (high-speed type)
  • Missing-message codes in modules on other networks

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–800
Time1–5 h

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

Parts involved

bus c wiringcan transceiver

Related codes

U0040U0046U0048U0050U0052

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