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Home / DTC / U0632 — Lost Communication With Fan 1

U0632 — Lost Communication With Fan 1

Detailed page for trouble code U0632.

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22,461specific
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U0632

Generic U — Network/User

Lost Communication With Fan 1

Brand: Generic
Type: U — Network/User
Views: UK: 24 EN: 98 RU: 32
AI status
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Page language: EN

Causes

  • Opened/blown fuse or tripped relay supplying Fan 1 module
  • Power or ground fault at the Fan 1 module (open, high resistance, intermittent)
  • Damaged, corroded, or disconnected connector at the fan module
  • Broken, shorted, or high-resistance CAN/LIN wiring between controllers
  • Missing or failed termination resistor on the CAN bus
  • Failed Fan 1 module (electronics internal fault)

Symptoms

  • Radiator/cooling fan 1 may not run or runs only on default mode
  • Engine temperature higher than normal or occasional overheating
  • HVAC performance reduction (increased A/C condenser temperature)
  • One or more network-related diagnostic trouble codes present
  • Fan control not responsive to commands from scan tool
  • Possible MIL or warning indicator depending on vehicle

What to check

  • Read all network modules with a capable scan tool; note related U-codes and freeze frame data
  • Visually inspect connectors and wiring at the Fan 1 module for corrosion, damage, or water intrusion
  • Verify fuses and relays supplying the fan module are good and seated
  • Measure module supply voltage at the fan connector (battery voltage with ignition on)
  • Check ground continuity for the fan module to chassis battery negative
  • Check CAN bus voltages: CAN_H ~2.5V (recessive) and CAN_L ~2.5V; dominant states near 3.5V/1.5V respectively

Signal parameters

  • Module supply voltage: approx. battery voltage (11–14V) with ignition on
  • Ground: near 0V to chassis
  • CAN bus idle (recessive): CAN_H ≈ 2.5V, CAN_L ≈ 2.5V
  • CAN bus dominant: CAN_H ≈ 3.5V, CAN_L ≈ 1.5V (differential ≈ 2.0V)
  • Termination resistance (both ends): ≈ 60 ohms across CAN_H and CAN_L
  • Message frequency: depends on vehicle — expected periodic status messages from fan module; absence indicates loss of communication

Diagnostic algorithm

  1. Capture freeze frame and note additional U-codes. Check if code is current or historic.
  2. Visually inspect Fan 1 module connector, wiring, and nearby harness for damage, corrosion, or water intrusion. Repair any obvious issues.
  3. Verify fuses and relays supplying the fan module; replace if blown or suspect.
  4. With ignition ON, measure supply voltage and ground at the fan module connector. Repair any open/high-resistance circuits.
  5. Use a scan tool to check for Fan 1 module presence/response. If the module is visible but not responding to commands, record module status and error frames.
  6. Measure CAN_H and CAN_L at the fan module connector with a digital multimeter and/or oscilloscope. Confirm recessive/dominant voltages and check for excessive noise or short to Vbatt/GND.
  7. Check termination resistance across CAN_H and CAN_L (~60 ohms). If out of range, inspect termination resistors or modules at each bus end.
  8. If wiring and power/ground are good but communication is absent, isolate the fan module by disconnecting it and re-check the bus for restoration of normal voltages and other modules' communication.
  9. If the bus functions with the module disconnected, suspect the fan module (bench test or replace). If the bus remains faulty, trace and repair wiring or replace failing module causing bus fault.
  10. After repair, clear codes, verify communication with scan tool, and perform a functional test (command fan on/off, verify operation). Road test and re-scan to confirm the issue is resolved.

Likely causes

  • Loose, corroded, or disconnected connector at the fan module
  • Power or ground loss to the fan controller (fuse, wiring)
  • Faulty or intermittent fan controller module
  • Damaged CAN high/low wiring or poor termination causing loss of messages
  • CAN bus short to battery or ground at or near the fan connector

Fault status

⚠️ Status
No communication received from Fan 1 controller on the vehicle data bus. The controlling module cannot obtain fan 1 status or command responses.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

U0100 U0121 U0140 U0155 U0073
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