U0003
High Speed CAN Communication Bus (+) Open
The CAN-High line of the high-speed bus is open. Without the differential pair, the controller cannot decode any traffic and reports loss of all participating modules at once. Often follows a wiring repair, accident damage, or a corroded connector pin.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
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
Common causes
Ordered by how often each turns out to be the cause.
- CAN-High wire broken or pin pushed backCommon
- Corroded module connectorPossible
- Harness damage after repair or accidentPossible
Parts involved
- CAN High Wire
- Module Connector
- CAN Transceiver
U0003 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.