OBD-II trouble code
U0007: High Speed CAN Communication Bus (-) Low
The CAN-Low (negative) line of the high-speed bus is reading too low — usually shorted to ground or dragged down. The collapsed differential disrupts communication across the network.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $100 – $900
- DIY difficulty
- Shop recommended
What does U0007 mean?
U0007 means the high-speed CAN bus's negative line — CAN-Low or CAN(-) — is sitting at a voltage that's too low for valid communication. On a healthy bus, CAN-Low rests near 2.5 volts and drops toward roughly 1.5 volts when a module is signaling. If something pulls that line below its normal range — typically a short to ground — the voltage difference between CAN-High and CAN-Low can no longer be read correctly and bus traffic breaks down.
This is the CAN-Low counterpart to U0008 (CAN-Low too high) and U0006 (CAN-Low open). Because CAN-Low already swings downward during normal signaling, a hard short to ground holds it at the bottom of its range and prevents the differential from forming properly. The cause is most often a wiring or connector fault that creates an unintended path to ground, though a failing module loading the line can read the same way. Modules that detect corrupted or missing traffic store U0007, often with module-specific lost-communication codes alongside.
Since CAN ties together the engine, transmission, ABS, cluster, and body modules, a low CAN-Low line can knock out several systems at once. Expect multiple warning lights, possible no-start or limp mode, and a scan tool that struggles to reach the affected modules. U0007 is traced electrically — measuring bus voltages and resistance and isolating the short — rather than by replacing parts on a guess.
Common causes
- CAN-Low wire shorted to ground
- Chafed or pinched CAN-Low wire contacting a grounded surface
- Water intrusion or corrosion creating a low-resistance path to ground
- Backed-out terminal allowing the wire to touch chassis metal
- A failed module loading the CAN-Low line down
- Damaged terminating resistor branch biasing the bus low
- Harness damage from an accident or prior repair shorting CAN-Low to ground
Symptoms
- Multiple warning lights on simultaneously (check engine, ABS, traction, airbag)
- Engine may not start, or runs in limp mode
- Erratic, frozen, or dead gauges
- Scan tool cannot communicate with several modules
- Module-specific lost-communication U-codes stored with U0007
- Intermittent loss of features that tracks with vibration or moisture
Diagnostic steps
- 1.Record all stored codes in every module to see which are affected and help localize the short.
- 2.Key on, measure CAN-Low voltage. It should rest near 2.5 volts; a reading dragged well below that points to a short to ground.
- 3.With key off and battery disconnected, measure bus resistance at the OBD port — about 60 ohms is healthy; near zero indicates a short.
- 4.Inspect the CAN-Low wire for chafing, pinch points, and contact with grounded metal.
- 5.Check connectors for water intrusion and corrosion that could create a path to ground.
- 6.Disconnect modules one at a time while watching the CAN-Low voltage; if it recovers when one is unplugged, that module is loading the bus down.
Repair cost
$100 – $900
Diagnosis commonly runs $150-$300 to isolate where the line is being pulled low. A wiring or connector repair to clear a short to ground is often $150-$600. If a failed module is loading the bus, replacement with programming can run $400-$900 or more, higher on European and luxury platforms.
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.