What it means
A high signal fault has been detected on the positive line of the medium-speed CAN communication bus. 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 medium-speed CAN network carries data between vehicle modules on CAN-High (+) and CAN-Low (-). U0019 indicates that CAN-High is being detected at an abnormally high level, which can occur when the line is shorted to battery voltage.
Common causes
Most likely first.
- CAN-High 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
- Use a scan tool to capture freeze-frame data and all communication codes, identifying which medium-speed CAN modules have stopped responding.
- Note whether the fault started after repairs or accessory installation, when a CAN-High wire may have been disturbed.
- Inspect CAN-High wiring and connectors for damaged insulation, pinched sections, or contact with a power feed.
- With the network powered down as directed by the manufacturer, test CAN-High for an unintended connection to battery supply and isolate sections to locate it.
- Verify termination and gateway routing using the vehicle wiring diagram only after checking for CAN-High voltage intrusion.
Common fixes
- Repair CAN-High wiring shorted to a battery feed.
- Replace damaged connector terminals or insulation and reroute the harness away from power wiring.
- Repair a terminating resistor only when network testing confirms it is out of specification.
- Correct a verified gateway routing problem according to the manufacturer's procedure.
Can I keep driving?
Do not continue driving if the communication fault disables safety-related functions or causes unpredictable vehicle behavior. If the vehicle is otherwise controllable, keep the trip short and arrange prompt diagnosis because the high CAN-High signal can disrupt multiple modules.
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.