What it means
A short between the positive and negative lines of the low-speed CAN communication bus has been detected. 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 uses CAN-High (+) and CAN-Low (-) together to carry messages between modules. U0023 indicates the two lines are electrically shorted together, which can corrupt communication or take affected low-speed modules offline.
Common causes
Most likely first.
- CAN-H/CAN-L 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
- Save freeze-frame data and all module communication codes, then note which low-speed network modules cannot be reached.
- Check whether the affected functions share a low-speed CAN branch and whether the fault followed recent harness work.
- Inspect both CAN-High and CAN-Low wires and connectors along that branch for crushed insulation, exposed conductors, or bridging corrosion.
- With the network powered down as the manufacturer specifies, test for an unintended connection between CAN-High and CAN-Low and isolate sections to locate the short.
- Check termination and gateway routing after confirming the two bus wires are not touching.
Common fixes
- Separate and repair CAN-High and CAN-Low conductors that have shorted together.
- Replace damaged connector terminals or wiring and secure the harness against further chafing.
- Replace a terminating resistor only if testing shows it is out of specification.
- Correct a confirmed gateway routing fault using the manufacturer's diagnostic procedure.
Can I keep driving?
Do not drive if lost network functions affect vehicle safety or control; the short can interrupt communication to multiple modules. If the vehicle remains safe and predictable, restrict use and 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.