Network, generic (extended)

U350D Control Module Cooling Fan Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U350D is set when the voltage or current feedback in a control module's fan circuit sits below the window the module expects. Usually the fan supply or control wire touches ground, or the motor itself has shorted turns, so the output stage limits current or switches off and the fan stands still; a blown fan fuse produces the same picture. Electronics with a dedicated fan exist, for example the charger of the 2021 Toyota RAV4 Prime with its fan speed sensor (T-SB-0021-21), and CARB demands that electrical outputs cooling inverters and batteries be checked for circuit faults. No manufacturer publishes U350D. Once warm, the module will most likely protect itself by lowering its output. An open circuit is U350C, a short to voltage U350E.

Likely causes

Fan supply or control wire chafed through to ground
Fan motor with shorted windings drawing excess current
Fan fuse blown as a result of the short
Output stage in the module pulling the line low

Symptoms

  • Module fan does not run
  • Reduced function or shutdown of the module when hot
  • Blown fan fuse

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€30–500
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

module cooling fanfan wiring

Related codes

U350CU350EU350FP0691

References: law.cornell.edu, static.nhtsa.gov.