CAN High Speed Bus Performance Issue
The U0002 code indicates a performance problem on the high-speed Controller Area Network (CAN) bus. This network allows various electronic control modules (ECUs) to communicate without a central host. Specifically, this code means a control module has detected degraded performance or intermittent interruptions in data transmission on the high-speed bus, often resulting in delays, packet loss, or electrical noise. Unlike open or short circuit faults, a performance failure is dynamic and may not completely shut down communication, but it disrupts timing enough to cause errors per SAE J2012. This prevents modules from receiving information on time, leading to intermittent symptoms in critical vehicle systems.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Damaged high-speed CAN bus wiring (cracks, corrosion, or excessive resistance)
- Poor connections at control module connectors (loose or dirty pins)
- Electromagnetic interference (EMI) or electrical noise affecting the network (e.g., proximity to unshielded high-voltage wires like spark plugs or alternator)
- Terminating resistors (120 ohms) out of specification or damaged
- One or more control modules on the network (ECU, TCM, ABS, etc.) experiencing internal delays or intermittent failure
- Power supply issues (fluctuating or low system voltage) affecting CAN transceiver performance
3. Symptoms You Will Notice
- Intermittent warning lights (Check Engine, ABS, etc.)
- Erratic transmission shifting or delayed response
- Stalling or rough idle
- Loss of communication with scan tool or modules
4. Step-by-Step Diagnosis
Scan for all stored codes and freeze frame data
Inspect CAN bus wiring for damage, corrosion, or loose connections
Check terminating resistor values at the OBD2 connector (should be ~60 ohms between CAN High and CAN Low)
Perform a network integrity test using an oscilloscope to look for signal noise or voltage drops
Isolate the faulty module by disconnecting modules one at a time and monitoring the bus
5. Frequently Asked Questions
Is it safe to drive?▼
Driving is not recommended as the issue can cause intermittent loss of communication with critical systems like the engine or transmission, potentially leading to stalling or unsafe driving conditions.
How much does it cost to fix?▼
Repair costs typically range from $150 to $600, depending on the root cause. Simple wiring repairs may be under $200, while replacing a faulty module can exceed $500.