U0024: Low-Speed CAN Bus Open Circuit
The U0024 code indicates an open circuit in the low-speed Controller Area Network (CAN) bus, also known as CAN-B or comfort CAN. This bus operates at 125 kbps and connects non-safety-critical modules such as climate control, infotainment, power seats, and door modules. An open circuit means there is a physical break in one or both of the bus wires (CAN-L and CAN-H), preventing communication between the modules on this network. According to SAE J2012, U0024 is a data bus communication fault specific to the low-speed CAN bus.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Damaged, cut, or corroded CAN bus wiring
- Faulty or damaged connector or splice in the harness, including a failed termination resistor
- Internal failure of the low-speed CAN transceiver in a control module
- Open or out-of-specification termination resistor on the low-speed CAN bus (typically 120 ohms each, 60 ohms in parallel)
- Moisture or corrosion in low-speed CAN bus connectors
- Short to ground or power on CAN wires that has evolved into an open circuit
3. Symptoms You Will Notice
- Malfunction of comfort systems such as power windows, door locks, or climate control
- Illuminated check engine light or other warning lights
- Communication errors or loss of function in infotainment or instrument cluster
4. Step-by-Step Diagnosis
Scan for all stored codes and note any related U-codes or module communication failures.
Visually inspect the low-speed CAN bus wiring and connectors for damage, corrosion, or loose connections.
Measure resistance between CAN-H and CAN-L at the OBD2 DLC or a convenient module; should be approximately 60 ohms.
Check for continuity in each CAN wire from end to end to locate the open circuit.
Isolate the faulty section by disconnecting modules one at a time and monitoring resistance changes.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive short distances, but comfort features like climate control, power windows, and infotainment may not work properly. Have the issue diagnosed soon to prevent further electrical problems.
How much does it cost to fix?▼
Repair costs typically range from $150 to $600, depending on the cause. Simple wiring repairs may cost $150-$300, while replacing a faulty module can run $400-$600 or more.