U0023 indicates that the low-speed CAN communication bus is detecting a persistently high voltage condition (CAN_H line stuck near battery voltage). This usually means a short to power, a damaged wire, or a faulty transceiver is preventing normal communication between body‑control modules.
Damage to the wiring harness (chaffing, rodent bite, or pinched wire) can cause the CAN_H line to be shorted to +12 V, pulling the bus high.
Connectors at the body control module, gateway, or other modules may develop corrosion or loose pins, creating a high‑resistance path that raises the bus voltage.
The internal CAN transceiver chip in a body‑control module, gateway, or related ECU can fail and drive the CAN_H line high, disrupting bus communication.
Sections of the low‑speed CAN harness that rub against metal brackets or sharp edges can develop intermittent shorts to power.
Add‑on accessories (e.g., aftermarket alarms, lighting) tapped into the CAN bus can introduce a fault that pulls the bus high if wired incorrectly.
While possible, a fault in the powertrain control module that holds the CAN_H line high is rare; it should be considered only after all wiring and transceiver causes are ruled out.
No. PCM/ECM failure is an uncommon cause of this code. Most U0023 issues stem from wiring shorts, corroded connectors, or faulty transceiver modules in body‑control nodes. Replacing the PCM without first checking those items often leads to unnecessary expense and does not resolve the problem.
A blown fuse will usually cut power to the affected modules, resulting in loss of communication rather than a high‑voltage condition. While a missing power supply can trigger related codes, it does not directly cause the bus to read high, so a fuse is not a typical cause of U0023.
A basic digital multimeter capable of measuring voltage and resistance is sufficient for the initial checks. An oscilloscope can provide a clearer view of the bus waveform, but it is not required for most diagnostic steps.
Once the fault is repaired, the code should clear on its own after a few drive cycles, or it can be cleared with a scan tool. If the code returns, the repair did not fully address the underlying issue.