What it means
The two lines of differential bus B are shorted together. 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 sends data using a differential pair: its (+) and (−) conductors carry complementary signals. U0045 indicates that those two lines are shorted together, preventing their signals from differing as intended and disrupting communication across the affected bus section.
Common causes
Most likely first.
- Bus lines shorted together
- 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 all codes and freeze-frame data and note which bus B modules become unreachable when the short is present.
- Inspect accessible bus B harnesses and connectors for crushed insulation, pinched wires, bent pins, or repairs that may have joined the (+) and (−) lines.
- Use scan-tool network status and the wiring diagram to identify which bus section and modules share the communication loss.
- With power isolated as specified by the manufacturer, test for continuity between bus B (+) and (−) and segment the harness to locate the short.
- If the conductors are not shorted in the harness, check gateway and module connectors for internal bridging and verify termination using the service information.
Common fixes
- Separate and insulate bus B (+) and (−) conductors where they have rubbed or been pinched together.
- Repair or replace a damaged connector with bridged terminals.
- Replace a harness section with an internal short between the paired lines.
- Repair a module or gateway only if isolation tests show the short is inside that component.
Can I keep driving?
Do not drive if the bus fault has disabled steering, braking, stability control, or another essential system; arrange recovery. If the vehicle remains controllable, keep trips short because communication loss may disable additional functions or trigger 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.