U0049 code meaning
Vehicle Communication Bus C (+) Low
What U0049 means
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.
U0049 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0049
- All functions on Bus C fail together (high-speed type)
- Missing-message codes in modules on other networks
Common causes of U0049
- Most likely(+) wire of Bus C chafed through to ground
- PossibleHarness pinched during assembly or repair
- Less likelyShorted transceiver in a module on Bus C
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus c wiringCAN transceiver
What each part of U0049 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 49 | The exact fault in that area. |
What to do next
- Note U0049 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0049
What does U0049 mean?
U0049 means "Vehicle Communication Bus C (+) Low". U0049 reports the (+) wire of Vehicle Communication Bus C shorted to ground. It is a generic code, so it means the same on every make.
Is it safe to drive with U0049?
Drive gently and only to a workshop. With U0049 the car can go into limp mode (reduced power) to protect itself.
Will U0049 fail an emissions test?
U0049 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0049 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will U0049 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.