What it means
Bus B low-side line voltage above expected range. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
Bus B carries module messages over paired lines, including the (−) low-side conductor. U0044 means the negative line is detected above its expected voltage range, which can prevent the connected modules from exchanging reliable data.
Common causes
Most likely first.
- Wire shorted to battery
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Record codes and freeze-frame data and identify which bus B modules lose communication when the high-voltage condition appears.
- Inspect bus B (−) wiring and connectors for a short to a power feed, damaged insulation, bent pins, or an incorrect prior repair.
- Check live network status with a scan tool and note whether the fault is constant or changes with harness movement or module activity.
- Use the manufacturer's procedure to measure the negative line and check for a short to battery or another power source.
- If the harness tests correctly, check gateway routing, termination, and affected module transceivers against the manufacturer's specifications.
Common fixes
- Repair bus B (−) wiring shorted to power.
- Replace damaged connector terminals or correct a bridged connection.
- Repair improperly joined or routed bus wiring.
- Repair the gateway or replace a module only if circuit tests confirm it is the source of the high reading.
Can I keep driving?
Stop driving and arrange recovery if the fault disables steering, braking, stability control, or another essential function. Otherwise, limit driving because communication failures can cause connected systems to shut down or enter limp mode.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.