U0049Vehicle Communication Bus C (+) Low
- Generic OBD-II code · Network
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- All functions on Bus C fail together (high-speed type)
- Missing-message codes in modules on other networks
- Likely causes
- Likely(+) wire of Bus C chafed through to ground
- PossibleHarness pinched during assembly or repair
- RareShorted transceiver in a module on Bus C
- Repair
- Hard · Usually a job for a workshop.Typical cost: €60 – €800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.