What it means
The low-speed CAN communication bus has entered a bus-off state. The affected functions depend on the vehicle network layout.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
The low-speed CAN network exchanges messages among connected vehicle modules. U0024 sets when the network enters a bus-off state, in which a controller stops transmitting because repeated communication errors have exceeded its error handling limits.
Common causes
Most likely first.
- Wiring short keeps bus in bus-off
- One failing node spamming errors
- Gateway module routing CAN messages incorrectly
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 freeze-frame data and all network codes, including which low-speed modules went offline and when the bus-off event occurred.
- Check whether the bus-off state returns after clearing codes and identify whether it affects the whole low-speed network or one branch.
- Inspect low-speed CAN wiring, connectors, and grounds for shorts, damage, corrosion, or loose connections that could generate repeated errors.
- Use the scan tool and manufacturer network procedure to identify whether one module is repeatedly transmitting errors or disrupting the bus.
- Check gateway routing and network termination against the wiring information after wiring faults and a failing node have been assessed.
Common fixes
- Repair wiring shorts or damaged low-speed CAN connections that trigger repeated communication errors.
- Clean and secure corroded or loose network connectors and grounds.
- Repair or replace a module only after diagnostics identify it as the source of bus errors.
- Correct a confirmed gateway routing or termination fault according to the manufacturer's procedure.
Can I keep driving?
Avoid driving if the bus-off event disables safety or control functions, or if warnings and behavior are unpredictable. Even if the vehicle currently operates, communication may drop again and disable additional functions, so arrange prompt diagnosis.
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.