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Home / DTC / U1500 — Control Module Communication Bus Malfunction

U1500 — Control Module Communication Bus Malfunction

Detailed page for trouble code U1500.

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U1500

Generic U — Network/User

Control Module Communication Bus Malfunction

Brand: Generic
Type: U — Network/User
Views: UK: 1 EN: 3 RU: 1
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Page language: EN

Causes

  • Open or short in communication bus wiring (CAN H/CAN L or single-wire bus)
  • Failed or intermittent control module(s)
  • Poor battery supply or weak/poor ground connections
  • Missing or damaged termination resistor(s)
  • Water intrusion, corrosion, or damaged connectors on the bus
  • Aftermarket device or improperly installed module interfering with bus

Symptoms

  • Malfunction indicator lamp or multiple warning lights illuminated
  • Loss of specific subsystem functions controlled by one or more modules (e.g., ABS, steering, instrument cluster)
  • Unable to communicate with one or more modules using a scan tool
  • Intermittent faults that appear/disappear with vibration or moisture
  • Modules show as ‘bus off’ or ‘no response’ in diagnostics

What to check

  • Read all U‑codes and freeze frame data with a capable scan tool; record which modules are not responding
  • Check battery voltage (key on and cranking); ensure >12V at the beginning of diagnosis
  • Visually inspect connectors, grounds, and wiring along the bus for corrosion, breaks, or pinch points
  • Check for aftermarket modules/devices connected to the bus and disconnect if present
  • Measure termination resistance between CAN_H and CAN_L with ignition off (expected ≈60Ω for CAN)
  • Backprobe CAN_H and CAN_L with a multimeter and/or oscilloscope to observe idle and active voltages

Signal parameters

  • CAN bus idle: CAN_H ≈2.5V, CAN_L ≈2.5V (difference ≈0V)
  • CAN dominant: CAN_H ≈3.5V, CAN_L ≈1.5V (difference ≈2V)
  • Typical CAN termination: two 120Ω resistors in parallel → ≈60Ω measured between CAN_H and CAN_L (key off)
  • Common CAN data rates: 125 kbps, 250 kbps, 500 kbps, 1 Mbps — bus messages should match vehicle data rate
  • LIN idle: single wire ≈12V (through pull-up); dominant ≈0V (varies by vehicle) — consult manufacturer spec for single-wire buses
  • Check for voltage spikes or noise on bus lines during operation (oscilloscope)

Diagnostic algorithm

  1. Record all active and stored codes and note which modules are not responding to the diagnostic tool.
  2. Verify good battery voltage and solid engine/chassis grounds; charge battery if low and recheck communications.
  3. Perform a visual inspection of the entire communication bus: connectors, splices, modules, and any T‑tap or aftermarket connections. Repair visible damage.
  4. With ignition off, measure resistance between CAN_H and CAN_L at a central point; expect ≈60Ω. If open or very low, isolate wiring sections to find a short or open.
  5. With ignition on, backprobe CAN_H and CAN_L at several modules with a multimeter/oscilloscope. Confirm idle voltages ~2.5V and dominant swings when messages occur. If one node holds bus dominant or shows missing signals, suspect that module.
  6. Disconnect suspect modules one at a time (after checking service information) to see if bus communication returns; remove aftermarket devices first.
  7. Wiggle harnesses and connectors while monitoring communication for intermittent faults; inspect for moisture intrusion and re-test after drying if needed.
  8. If a failed module/transceiver is identified, replace or reprogram per manufacturer procedures. After repairs, clear codes and perform a road test and extended system verification.
  9. If diagnostics are inconclusive, use a capable scope and bus analyzer to capture and decode traffic, or consult wiring diagrams/gateway architecture for further isolation.

Likely causes

  • Damaged connector or pin at a gateway/ECU
  • Corroded CAN/LIN wiring harness splice or chafed wire shorting to ground
  • One module pulling the bus dominant (shorted transceiver)
  • Failed termination resistor (open or incorrect value)
  • Low battery voltage or poor engine/chassis ground affecting module communication

Fault status

⚠️ Status
Control module communication bus malfunction detected. One or more modules are not communicating properly on the vehicle data bus; check wiring, termination, and individual module transceivers.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0073 U0074 U0140 U0401
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