OBD-II trouble code
U0016: Medium Speed CAN Communication Bus (-) Low
The negative (CAN-Low) wire of the medium-speed communication bus is reading too low — usually shorted to ground or dragged down. The weakened differential disrupts messages between body and comfort modules.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $800
- DIY difficulty
- Shop recommended
What does U0016 mean?
U0016 means the negative line — CAN-Low or CAN(-) — of the medium-speed CAN bus is sitting at a voltage that is too low for valid communication. CAN-Low normally rests near 2.5 volts and dips toward roughly 1.5 volts when a module signals. If something pulls that line down further than it should go — most often a short to ground — the voltage difference between CAN-High and CAN-Low can no longer be read reliably and traffic on that bus breaks down.
Many vehicles use a slower medium-speed bus, separate from the high-speed powertrain network, to link body, comfort, infotainment, and convenience modules where timing is less critical. U0016 is the medium-speed counterpart to U0007 on the high-speed bus, and the CAN-Low sibling of U0013 on the same medium-speed network: it names a 'low' fault specifically on the negative conductor. The usual cause is a wiring or connector fault that creates an unintended path to ground, though a failing module loading the line down can read the same way.
Because the medium-speed bus generally carries comfort features rather than core driving systems, U0016 tends to be less severe than a high-speed fault. The car usually still starts and drives, but you may lose climate control, audio, displays, or power accessories, and several lost-communication U-codes can set together. It is traced electrically — measuring bus voltage and resistance to find where the line is pulled low — rather than by replacing parts on a guess.
Common causes
- CAN-Low wire on the medium-speed bus 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 letting the wire touch chassis metal
- A failed module loading the CAN-Low line down
- Damaged terminating-resistor branch biasing the bus low
- Harness damage from prior repair or accident shorting CAN-Low to ground
Symptoms
- Comfort/convenience features stop working (climate, infotainment, accessories)
- Driver displays freeze, blank, or show fault messages
- Multiple lost-communication U-codes stored with U0016
- Scan tool struggles to reach modules on the medium-speed bus
- Intermittent loss of features that tracks with vibration or moisture
- Engine usually still starts and runs normally
Diagnostic steps
- 1.Record all stored codes in every module to see which medium-speed modules are affected and help localize the short.
- 2.Identify which modules sit on the medium-speed bus for the specific vehicle using wiring diagrams.
- 3.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.
- 4.With key off and battery disconnected, measure bus resistance — about 60 ohms is healthy; a reading near zero indicates a short.
- 5.Inspect the CAN-Low wire for chafing, pinch points, and contact with grounded metal, and check connectors for corrosion and water intrusion.
- 6.Disconnect modules one at a time while watching CAN-Low voltage; if it recovers when one is unplugged, that module is loading the bus down.
Repair cost
$100 – $800
Diagnosis to isolate where the line is pulled low commonly runs $100-$250. A wiring or connector repair to clear a short to ground is often $150-$550. If a failed module is loading the bus, replacement with programming can run $400-$800+, higher on luxury and European 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.