Low Speed CAN Bus High Line Fault
Diagnostic trouble code U0026 indicates a fault in the low-speed Controller Area Network (CAN) bus, specifically on the high signal line (CAN-H). The low-speed CAN bus, also known as CAN-B or comfort CAN, typically operates at 125 kbps and manages non-safety-critical modules such as climate control, seats, doors, and infotainment systems. Detection of a low voltage on the CAN-H line suggests an open circuit, short to ground, or bus termination failure that prevents proper communication between 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
- Damaged, cut, or shorted-to-ground CAN-H wiring
- Short circuit between CAN-H and CAN-L lines
- Bus termination resistor out of specification (failed or missing)
- Internal control module failure affecting the communication bus
- Corroded, oxidized, or retracted pin in harness connector or splice
- External electromagnetic interference altering the signal
3. Symptoms You Will Notice
- Malfunctioning comfort systems (e.g., climate control, power seats, door locks)
- Infotainment system failures or intermittent operation
4. Step-by-Step Diagnosis
Scan all modules for communication faults and verify U0026 is active
Inspect CAN-H wiring for damage, corrosion, or shorts using a multimeter
Check bus termination resistance at the OBD2 connector (should be ~60 ohms with two 120-ohm resistors in parallel)
Disconnect modules one by one to isolate the faulty module affecting the bus
Repair or replace damaged wiring, connectors, or termination resistors as needed
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive short distances as the low-speed CAN bus controls comfort features, not critical safety systems. However, you may experience loss of functions like climate control or infotainment. Have it diagnosed soon to prevent further issues.
How much does it cost to fix?▼
Repair costs typically range from $150 to $600, depending on the root cause. Simple wiring repairs may cost $150-$300, while replacing a faulty module can run $400-$600 or more.