OBD-II trouble code
U0005: High Speed CAN Communication Bus (+) High
The CAN-High (positive) line of the high-speed bus is reading too high — usually shorted to battery or another voltage source. The elevated voltage corrupts the differential signal and disrupts the network.
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 U0005 mean?
U0005 means the high-speed CAN bus's positive line — CAN-High or CAN(+) — is sitting at a voltage that's too high for valid communication. CAN-High should rest near 2.5 volts and rise to roughly 3.5 volts only briefly while a module signals. If the line is instead pinned high — for example shorted to battery voltage or to a switched power circuit — the differential between CAN-High and CAN-Low is destroyed and modules can no longer decode bus traffic.
This is the 'high' counterpart to U0004 (CAN-High too low) and U0003 (CAN-High open). A high condition almost always traces to a wire that has shorted to a power source: a chafed CAN-High conductor touching a hot wire, water bridging a connector to an adjacent powered pin, or harness damage that brings the bus into contact with battery voltage. Less often, a failed module drives the line high. The modules that detect the corrupted bus store U0005, frequently alongside module-specific lost-communication codes.
Because CAN connects the engine, transmission, ABS, instrument cluster, and body modules, a high CAN-High line can disable several systems at once. Expect multiple warning lights, possible no-start or limp mode, and a scan tool that can't reliably reach the affected modules. Note that a short to a power source can also damage modules on the bus, so the repair sometimes goes beyond the wiring itself. U0005 is diagnosed with a meter and wiring diagram, not by guessing at parts.
Common causes
- CAN-High wire shorted to battery voltage or a switched power circuit
- Chafed CAN-High conductor contacting a hot wire in the harness
- Water intrusion bridging CAN-High to a powered terminal in a connector
- Harness damage from an accident or repair bringing the bus into contact with power
- A failed module driving the CAN-High line high
- Incorrectly repaired or spliced harness routing power onto the bus
- Corrosion creating a high-resistance leak from a power source onto CAN-High
Symptoms
- Multiple warning lights illuminated at once (check engine, ABS, traction, airbag)
- Engine may crank but not start, or run in limp mode
- Dead, frozen, or erratic gauges
- Scan tool cannot communicate with several modules
- Module-specific lost-communication U-codes stored with U0005
- In severe cases, more than one module damaged by the short to power
Diagnostic steps
- 1.Record all stored codes across every module to identify the affected segment.
- 2.Key on, measure CAN-High voltage. It should rest near 2.5 volts; a reading pinned well above that points to a short to a power source.
- 3.Trace the CAN-High wire looking for chafe points, pinch damage, and contact with powered wires or terminals.
- 4.Inspect connectors for water intrusion and corrosion that could bridge CAN-High to a hot pin.
- 5.With key off and battery disconnected, check bus resistance (about 60 ohms healthy) and check for unexpected continuity between CAN-High and any power circuit.
- 6.Disconnect modules one at a time while watching CAN-High voltage; if it normalizes when one is unplugged, that module may be driving the line high.
- 7.After clearing the short, scan all modules — a short to power can damage modules, which may need further repair.
Repair cost
$100 – $1,200
Diagnosis typically runs $150-$300. Clearing a short to power in the wiring is often $150-$600. Because a short to battery voltage can damage modules on the bus, repairs sometimes extend to module replacement and programming at $400-$1,000+, higher on European and luxury vehicles.
Estimate your repair
Run the numbers for your vehicle
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.