U0044 code meaning
Vehicle Communication Bus B (-) High
What U0044 means
U0044 means the (-) conductor of Vehicle Communication Bus B is held at an excessive voltage, mostly through contact with battery plus. Where Bus B is a high-speed-type CAN, the conductor is CAN-Low, and onsemi found that with CAN-Low at 12 V no frame gets out any more; the node's current even drops, to about 48 mA, because its transmit pin is driven low only some 2 % of the time while the controller retries and backs off. All Bus B members fall silent together. A fault-tolerant low-speed CAN handles the same fault differently: NXP's TJA1055 detects it after a filter delay, turns off the CAN-Low driver and listens on CAN-High only. No manufacturer documents U0044 publicly. Ignition on, CAN-Low against ground near battery voltage confirms it; look for chafing at supply wires and water in connectors.
U0044 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 U0044
- All functions on Bus B fail together (high-speed type)
- Lost-communication codes in modules on other networks
- Fallback modes or warning lamps depending on the modules involved
Common causes of U0044
- Most likely(-) wire chafed against a battery or ignition feed
- PossibleWater in a connector linking the (-) wire to a supply pin
- Less likelyDamaged transceiver driving the (-) line high
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 U0044 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 44 | The exact fault in that area. |
What to do next
- Note U0044 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 U0044
What does U0044 mean?
U0044 means "Vehicle Communication Bus B (-) High". U0044 means the (-) conductor of Vehicle Communication Bus B is held at an excessive voltage, mostly through contact with battery plus. It is a generic code, so it means the same on every make.
Is it safe to drive with U0044?
Drive gently and only to a workshop. With U0044 the car can go into limp mode (reduced power) to protect itself.
Will U0044 fail an emissions test?
U0044 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 U0044 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will U0044 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.