U0023: CAN Bus High Voltage Fault
The U0023 code indicates that the ECU has detected an abnormally high voltage condition on the CAN High line of the low-speed CAN bus (ISO 11898-3). This bus typically controls comfort, body, and lighting systems. The fault can be caused by a short to battery voltage, an open circuit in the CAN High line, or an internal transceiver failure in one of the connected modules.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Short circuit of the CAN High line to battery voltage (B+)
- Open circuit in the CAN High line (broken wire or disconnected connector)
- Internal failure of the CAN transceiver in a module on the LS-CAN bus
- Damaged or missing bus termination resistor
- Corrosion or moisture in CAN bus connectors
- Faulty ECU that holds the line in an incorrect dominant/recessive state
3. Symptoms You Will Notice
- Malfunction of comfort systems (power windows, door locks, etc.)
- Body control module communication errors
- Lighting system failures (interior or exterior lights)
- Check Engine Light or other warning lights illuminated
4. Step-by-Step Diagnosis
Scan for all stored codes and freeze frame data
Visually inspect CAN bus wiring and connectors for damage, corrosion, or loose connections
Measure voltage on CAN High line (should be around 2.5V with bus idle)
Check for shorts to battery voltage or ground on CAN High and CAN Low lines
Test termination resistors (typically 120 ohms each) at the ends of the bus
Isolate modules by disconnecting them one at a time to identify the faulty module
5. Frequently Asked Questions
Is it safe to drive?▼
Driving is possible but not recommended, as the fault can cause intermittent failures in critical comfort and lighting systems, potentially affecting safety. Have the vehicle diagnosed and repaired promptly.
How much does it cost to fix?▼
Repair costs vary widely depending on the cause. Simple wiring repairs may cost $100-$300, while replacing a faulty module can range from $400 to $1,200 including labor.