What it means
An open 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 messages between body and other vehicle modules over paired CAN-High (+) and CAN-Low (-) wires. The module monitoring the network sets U0017 when it detects an open in the CAN-High line, disrupting communication on that network.
Common causes
Most likely first.
- CAN-High wire broken in body harness
- 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 record freeze-frame data and all module communication codes, then identify which medium-speed CAN modules are unreachable.
- Check whether the affected functions and communication faults began together, which can help distinguish a shared network fault from an individual module issue.
- Inspect the medium-speed CAN-High wire, connectors, and splices in the body harness for breaks, looseness, corrosion, or damage.
- With the vehicle powered down as specified by the manufacturer, test CAN-High continuity across the affected network section and compare with the manufacturer's specification.
- Check the network termination and gateway routing using the vehicle's wiring information and manufacturer diagnostic procedure before replacing a module.
Common fixes
- Repair a broken or damaged CAN-High wire in the body harness.
- Clean, secure, or repair corroded or loose CAN-High connectors and splices.
- Repair or replace a terminating resistor if testing shows it is out of specification.
- Correct a gateway routing fault only after wiring and network checks confirm it.
Can I keep driving?
Drive only if the affected functions are not needed for safe control and the vehicle behaves normally; multiple warnings or lost functions can include safety-related systems. Avoid unnecessary trips and arrange diagnosis promptly, since intermittent or lost network communication can disable more functions.
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.