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Home / DTC / U0016 — Medium Speed CAN Communication Bus (-) low

U0016 — Medium Speed CAN Communication Bus (-) low

Detailed page for trouble code U0016.

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22,491specific
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Code

U0016

MERCEDES-BENZ U — Network/User

Medium Speed CAN Communication Bus (-) low

Brand: MERCEDES-BENZ
Type: U — Network/User
AI status
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Page language: EN

Causes

  • Short to ground on Medium Speed CAN (CAN_L) wiring
  • Open or high-resistance CAN_L conductor or connector
  • Corroded/loose connector or water ingress at a module or splice
  • Faulty CAN transceiver in a module (module pulling CAN_L low)
  • Missing or incorrect termination (open/failed resistor)
  • Incorrect wiring after repairs or aftermarket device connected

Symptoms

  • Loss of communication with one or more control modules on the medium-speed CAN network
  • Multiple network-related DTCs appearing (U-codes) or intermittent functionality of affected systems
  • Malfunctions of modules tied to medium-speed CAN (e.g., gateway, body control, doors, climate, instrument cluster)
  • Possible warning lights on dash related to communication or affected systems
  • Noisy or erratic operation of affected systems

What to check

  • Read all stored, pending and permanent U-codes and note which modules report communication loss
  • Verify battery voltage and chassis ground integrity before testing (12.0–14.5 V expected while engine running)
  • Visually inspect CAN wiring, connectors, and splice points for damage, corrosion or water
  • Inspect for aftermarket modules or recent wiring repairs on the medium-speed CAN network
  • Measure idle voltages on CAN_H and CAN_L at central gateway and suspected modules
  • Check termination resistance between CAN_H and CAN_L (expected ~60 Ω total with two 120 Ω resistors in parallel)

Signal parameters

  • Recessive (idle) voltage: CAN_L ≈ 2.5 V (same as CAN_H ≈ 2.5 V) relative to ground
  • Dominant state: CAN_L drops toward ≈ 1.5 V while CAN_H rises toward ≈ 3.5 V
  • Expected differential voltage during dominant bits: ~2.0 V
  • Termination resistance between CAN_H and CAN_L: ~60 Ω (two 120 Ω terminators in parallel)
  • Low-line fault indication: CAN_L measured significantly below ~2.0 V at idle or stuck near ground

Diagnostic algorithm

  1. Record all network-related DTCs and module availability using a manufacturer-level scan tool. Note which modules are not communicating.
  2. Verify vehicle power and ground. Recheck codes after battery stable; some modules require wake/sleep cycles.
  3. Perform a visual inspection of CAN wiring, connectors, and known trouble areas (doors, gateway, junction boxes). Repair obvious damage.
  4. Backprobe the medium-speed CAN pair at the gateway and an affected module. With ignition ON, measure CAN_L idle voltage. If CAN_L is significantly below ~2.5 V, suspect short to ground or faulty transceiver.
  5. Measure resistance to ground on CAN_L with battery disconnected. Low resistance indicates a short to ground. Isolate by disconnecting connectors or modules to find which segment shows the low resistance.
  6. Check termination resistance across CAN_H and CAN_L with ignition off and battery disconnected; expect ~60 Ω. Open or incorrect value suggests missing/failed terminator(s).
  7. Use an oscilloscope to verify waveform quality and identify a module pulling the line dominant. Observe for excessive dominant time or collisions.
  8. If isolating a suspect module, disconnect that module (per service manual procedures) and recheck bus voltages and communication. Replace or repair only after confirming isolation removes the fault.
  9. Repair damaged wiring, replace corroded connectors, restore proper terminations, and replace any module with confirmed faulty CAN transceiver.
  10. Clear codes, perform network learn or programming if required, and verify repair with a road test and re-scan.

Likely causes

  • Wiring damage (chafing, pinched, rodent damage) causing CAN_L short or open
  • Corroded connector at a module on the medium-speed CAN bus
  • Failed or intermittent module CAN transceiver (gateway, control module)
  • Faulty termination resistor (open or changed value)
  • Aftermarket accessory improperly connected to CAN network

Fault status

⚠️ Status
Medium Speed CAN bus low voltage detected (CAN_L low). Communication errors present on medium-speed CAN network; fault active when CAN_L below threshold or bus signaling invalid. Stored when condition repeats or persists.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0010 U0073 U0100 U0115 U0121
856

Browse 856 MERCEDES-BENZ manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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