Powertrain, generic · Auxiliary emission controls

P0494 Fan 1 Underspeed

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Two kinds of cooling fan carry these codes: electric fans switched by relays or driven by a PWM/LIN fan module with speed feedback, and engine-driven fans with an electronically controlled viscous clutch, whose speed a Hall sensor reports – GM calls them EV fans, meaning electro-viscous, not electric vehicle. P0494 means fan 1 turns slower than commanded, judged from the speed reported by a LIN fan module or the clutch's speed sensor. GM's 2.0-litre turbo of 2020 uses a lower limit of about 59 % of the target at 750 rpm, rising to about 76 % at 2750 rpm and above. GM bulletins name an internal fan fault on the Equinox/Terrain 1.5 and water slowing the fan on the Hummer EV; Ford's 6.7-litre Super Duty uses it for the viscous fan and warns against replacing the clutch too quickly.

Likely causes

Fan motor or fan module faulty or worn (brushes, bearings, electronics)
Fan slowed or blocked (water, snow, ice, foreign object, distorted shroud)
Viscous clutch slipping or low on fluid, clutch valve faulty
High-resistance supply or ground, connector problems
Faulty speed signal (sensor or LIN feedback)

Symptoms

  • Check engine light on (depending on the maker)
  • Temperature rises at standstill or when towing
  • Air conditioning weak at standstill

Repair estimate

DifficultyMediumDIY possible
Parts and labour€150–900
Time0.8–3 h

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

Parts involved

cooling fan 1fan clutchfan speed sensorengine control module

Related codes

P0495P0483P0493P0526P0529P0480

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, gsi.ext.gm.com.