U0632

Code

Generic U — Network/User

Lost Communication With Fan 1

Brand: Generic

Type: U — Network/User

Views: UK: 27 EN: 281 RU: 43

AI status

Completed

ready

Completed 100%

Page language: EN

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

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

Capture freeze frame and note additional U-codes. Check if code is current or historic.
Visually inspect Fan 1 module connector, wiring, and nearby harness for damage, corrosion, or water intrusion. Repair any obvious issues.
Verify fuses and relays supplying the fan module; replace if blown or suspect.
With ignition ON, measure supply voltage and ground at the fan module connector. Repair any open/high-resistance circuits.
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.
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.
Check termination resistance across CAN_H and CAN_L (~60 ohms). If out of range, inspect termination resistors or modules at each bus end.
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.
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.
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.