U0012 CAN Bus Medium Speed Open Circuit
The U0012 code indicates an open circuit fault in the medium-speed Controller Area Network (CAN) bus. This means the control module monitoring this bus has detected a physical break or disconnection in the communication line, preventing associated electronic modules from exchanging data properly. According to SAE J2012, this code falls under data communication network errors, specifically when circuit resistance is excessively high or infinite due to a cut in the wiring.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Open circuit in the medium-speed CAN bus wires
- Corroded, damaged, or loose electrical connectors on the CAN bus
- Damaged or open CAN bus termination resistor
- Faulty electronic control module on the medium-speed CAN network
- Short to ground or voltage in the communication line
3. Symptoms You Will Notice
- Check Engine Light or other warning lights illuminated
- Communication errors between modules, leading to erratic behavior or loss of functions
4. Step-by-Step Diagnosis
Use a scan tool to retrieve all stored codes and freeze frame data
Visually inspect the CAN bus wiring and connectors for damage, corrosion, or looseness
Measure resistance between CAN High and CAN Low terminals at the OBD2 connector (should be 60 ohms with two termination resistors)
Check for shorts to ground or voltage on the CAN bus lines
Test the termination resistors individually if resistance is out of spec
If wiring and resistors are good, suspect a faulty control module and perform module isolation tests
5. Frequently Asked Questions
Is it safe to drive?▼
Driving with a U0012 code is not recommended as it can cause unpredictable behavior in critical systems like transmission, ABS, or engine control, potentially leading to a safety hazard.
How much does it cost to fix?▼
Repair costs typically range from $100 to $500 for wiring repairs or connector replacement, but can exceed $1,000 if a control module needs replacement.