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DTC codes / U00xx · Network wiring and bus faults / U0044

U0044Vehicle Communication Bus B (-) High

U0044 is a generic network communication code indicating that the vehicle's communication bus B negative circuit is reading a high voltage, which means the controller area network (CAN) data line is stuck at or near battery voltage instead of toggling between high and low states. The computer detected an abnormal voltage level on the bus B minus wire, which prevents modules from exchanging data reliably.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaNetwork wiring and bus faults

Symptoms you may notice

  • Multiple warning lights illuminated on the dashboard, often including the check engine light, ABS, and airbag lights
  • Intermittent or complete failure of one or more electronic systems such as power windows, radio, or climate control
  • The engine may start and run, but other modules may not communicate with the scan tool
  • Erratic gauge readings or flickering instrument cluster displays
  • Often no symptoms besides the warning light if the fault is isolated to a single module or a shorted stub
  • The vehicle may enter limp mode or fail to start if the bus is completely shorted high

Common causes, most likely first

  1. A short to voltage on the bus B negative wire, often caused by chafed insulation rubbing against a power wire
  2. A failed module that is internally shorting the bus B minus line to battery voltage
  3. Corrosion or water intrusion in a connector on the bus B circuit, creating a high-resistance path to voltage
  4. A faulty termination resistor inside a module that is pulling the bus line high
  5. Damaged or pinched wiring harness along the bus B routing, especially near sharp edges or moving components
  6. A malfunctioning gateway module that is incorrectly driving the bus B negative line high

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes across every module to confirm U0044 is active and identify which modules are offline
  2. Measure the voltage on the bus B negative wire at the data link connector (DLC) with the key on and engine off, looking for a steady high voltage above 3.5 volts
  3. Disconnect modules one at a time from the bus and recheck the voltage to isolate a module that is shorting the line high
  4. Inspect the wiring harness along the bus B route for chafed insulation, pinched wires, or signs of contact with power circuits
  5. Check for water intrusion or corrosion in connectors on the bus B circuit and clean or replace as needed
  6. Test the termination resistors with an ohmmeter across the bus lines with the power off, expecting approximately 60 ohms total
  7. Repair or replace the faulty wiring, connector, or module, then clear codes and verify communication is restored on all modules

When bus B minus reads high

  • A common oversight is replacing the module that sets U0044 when the actual fault is a shorted wire in a different section of the harness, so always perform voltage checks before condemning any module.
  • The bus B negative line can read high if a module on a different bus segment is backfeeding voltage through a shared power or ground circuit, so check for related codes on other buses.
  • Aftermarket accessories such as remote starters or alarm systems spliced into the bus wiring are frequent culprits for a short to voltage on bus B minus.
  • A faulty alternator or voltage regulator can introduce electrical noise that mimics a high bus B minus signal, so check charging system ripple when the code is intermittent.
  • U0044 can be stored by a module that is simply unplugged or missing its power feed, not just by a shorted wire, so verify all modules on the bus are powered and grounded.

Can I keep driving with U0044?

If the vehicle starts and runs normally with only a warning light, you can drive it to a repair shop, but avoid using electronic features that may be affected and do not tow a trailer or rely on advanced driver aids. If multiple systems fail or the engine runs poorly, stop driving and have the vehicle towed to prevent unsafe operation.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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