P0494Fan 1 Underspeed
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Check engine light on (depending on the maker)
- Temperature rises at standstill or when towing
- Air conditioning weak at standstill
- Likely causes
- LikelyFan motor or fan module faulty or worn (brushes, bearings, electronics)
- PossibleFan slowed or blocked (water, snow, ice, foreign object, distorted shroud)
- PossibleViscous clutch slipping or low on fluid, clutch valve faulty
- PossibleHigh-resistance supply or ground, connector problems
- RareFaulty speed signal (sensor or LIN feedback)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €150 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.