CAN Bus High Voltage Fault
The U0008 code indicates that a control module has detected an abnormally high voltage on the CAN Low line of the high-speed CAN bus. This bus is a differential pair used for communication between electronic modules; when the voltage on CAN Low exceeds the expected threshold—typically due to a short to battery voltage or to the CAN High line—the differential signal is corrupted, and the fault is logged. This condition prevents reliable transmission of critical data between controllers, which can cause intermittent or permanent failures in systems such as the engine, transmission, ABS brakes, or airbags.
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 between the CAN Low wire and a battery positive (B+) circuit
- Short circuit between the CAN Low and CAN High wires
- Damaged CAN bus wiring, or corroded/moisture-contaminated connectors or terminals
- Missing or out-of-specification CAN bus termination resistor
- Faulty control module that alters the bus voltage reference
3. Symptoms You Will Notice
- Check Engine Light or other warning lights illuminated
- Intermittent or complete loss of communication with modules, leading to drivability issues, transmission shifting problems, or ABS/airbag malfunctions
4. Step-by-Step Diagnosis
Scan all modules for related communication codes and note which modules are offline.
Using a digital multimeter, measure the resistance between CAN High and CAN Low at the OBD2 connector (should be ~60 ohms with two termination resistors).
Check for voltage on CAN Low with key on, engine off: normal is ~2.5V; a reading near 5V or battery voltage indicates a short to power.
Inspect the CAN bus wiring and connectors for damage, corrosion, or moisture, especially in areas prone to rubbing or exposure.
If wiring is intact, isolate modules one by one to identify a faulty module causing the voltage pull-up.
5. Frequently Asked Questions
Is it safe to drive?▼
No, it is not safe to drive. The U0008 code indicates a high-severity communication fault that can cause sudden loss of critical systems like ABS, airbags, or engine control, leading to a potential safety hazard.
How much does it cost to fix?▼
The repair cost typically ranges from $150 to $600, depending on the root cause. Simple wiring repairs may be on the lower end, while replacing a faulty module can cost more.