U0043 code meaning
Vehicle Communication Bus B (-) Low
What U0043 means
U0043 reports the (-) line of Vehicle Communication Bus B shorted toward ground. Where Bus B is built like a high-speed CAN, that line is CAN-Low, and the fault is sneaky: onsemi measured frames still getting through, with distorted levels and the node drawing about 72 mA instead of 65 mA, because the CANH driver now pushes current through the termination into ground. NXP lists the case among hidden failures. NXP's fault-tolerant TJA1055 transceiver instead detects the short, switches off its CAN-Low driver and carries on single-wire over CAN-High. In both cases the vehicle tends to run normally, with the code logged by one module or showing up only now and then, which sets it apart from U0040, where the bus goes quiet. No manufacturer documents U0043 publicly; near-zero ohms from CAN-Low to ground confirms it.
U0043 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0043
- Vehicle mostly normal, code stored by a single module
- Occasional communication errors
Common causes of U0043
- Most likely(-) wire insulation damaged and touching ground
- PossibleHarness trapped under a panel or bracket
- Less likelyFaulty transceiver pulling the (-) line to ground
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus b wiringBus b transceiver
What each part of U0043 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 43 | The exact fault in that area. |
What to do next
- Note U0043 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 U0043
What does U0043 mean?
U0043 means "Vehicle Communication Bus B (-) Low". U0043 reports the (-) line of Vehicle Communication Bus B shorted toward ground. It is a generic code, so it means the same on every make.
Is it safe to drive with U0043?
U0043 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0043 fail an emissions test?
U0043 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 U0043 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will U0043 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.