OBD-II trouble code
U0002: High Speed CAN Communication Bus (Performance)
The high-speed CAN bus is communicating, but not reliably — messages are corrupted, delayed, or intermittent. Often a harder-to-find version of a full bus failure, frequently caused by marginal wiring or a flaky module.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $100 – $1,200
- DIY difficulty
- Shop recommended
What does U0002 mean?
U0002 is closely related to U0001, but where U0001 flags a general high-speed CAN bus fault, U0002 specifically points at a performance or rationality problem on that bus. In other words, the network is up and modules are talking, but the communication isn't clean: messages are arriving corrupted, error counters are climbing, the data rate is degraded, or traffic is dropping out intermittently. The modules can tell the bus isn't behaving the way the design expects, so they store U0002.
High-speed CAN is designed to tolerate a certain amount of error and keep running, with built-in error counters that escalate a module from 'error active' toward 'bus off' as faults accumulate. U0002 often appears when the bus is operating right at the edge of reliability — a partially chafed wire, a corroded connector with high resistance, a marginal terminating resistor, or a module whose transceiver is starting to fail and is injecting occasional bad frames. Because the fault is intermittent by nature, it can be one of the more frustrating network codes to chase: the symptoms come and go, often with temperature, vibration, or moisture.
The driver-facing symptoms mirror other CAN faults but tend to be sporadic. Warning lights may flicker on and off, gauges may glitch momentarily, and features may drop out and then return. Because a marginal bus can deteriorate into a complete failure without warning, U0002 should be diagnosed rather than ignored, even when the car still seems to drive normally between episodes.
Common causes
- Partially chafed or pinched CAN-High or CAN-Low wire causing intermittent shorting
- High-resistance or corroded connector terminal on the bus
- Marginal or partially failed terminating resistor
- A module with a failing CAN transceiver injecting corrupted frames
- Loose or backed-out terminals at a splice pack or junction connector
- Water intrusion that intermittently bridges bus circuits
- Poor module ground causing unstable signaling
- Aftermarket electronics or wiring spliced into the bus incorrectly
Symptoms
- Warning lights that flicker on and off rather than staying solid
- Intermittent gauge glitches or momentary dropouts
- Features that cut out briefly and then come back
- Occasional no-start or stalling that clears on a restart
- Scan tool communication that drops and reconnects
- Symptoms that correlate with bumps, temperature, or wet weather
- Multiple intermittent U-codes stored across modules
Diagnostic steps
- 1.Read freeze-frame and stored codes in all modules; note any conditions (temperature, road speed) recorded when U0002 set.
- 2.Measure bus termination resistance across CAN-High and CAN-Low (about 60 ohms is healthy) and watch for the reading drifting when wiring is wiggled.
- 3.Use an oscilloscope on CAN-High and CAN-Low to look for distorted waveforms, missing frames, or noise that a meter won't catch.
- 4.Perform a wiggle test on the harness and connectors while monitoring the bus to provoke an intermittent fault.
- 5.Inspect connectors and splice packs for corrosion, water, and loose terminals; clean and reseat as needed.
- 6.If a specific module's transceiver is suspected, disconnect modules one at a time and watch whether bus error rates improve.
Repair cost
$100 – $1,200
Because U0002 is often intermittent, diagnostic time is the biggest variable and commonly runs $150-$350. Repairing a chafed wire, corroded connector, or terminator is typically $150-$600. Replacing a module with a failing transceiver, including programming, runs $400-$1,000. Multi-bus European and luxury vehicles tend toward the high end due to harness complexity.
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Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.