Low Fan Speed
What Does It Mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles (Chevrolet, Buick, Peugeot, Toyota, Citroën, Dodge, BMW, Honda, Acura, Ford, Dodge, etc.). Although generic, specific repair steps may vary by make/model.
The fan manufacturers refer to in these codes is the cooling fan. Generally, the fan is mounted on the radiator. Its function is to cool the coolant in the radiator and help regulate engine temperature.
The Engine Control Module (ECM) or Powertrain Control Module (PCM) monitors/controls a multitude of sensors to monitor and regulate engine temperature. The ECM activates the fan when engine temperatures become high (e.g., idling in traffic) and turns it off when airflow is sufficient to maintain low temperatures (i.e., driving on the highway).
While monitoring the cooling fan, the ECM detected a low-speed condition. If the cooling fan spins beyond or below the parameters set by the manufacturer, the check engine light or Malfunction Indicator Lamp (MIL) will be illuminated by the ECM.
Diagnostic Codes Related to Engine Cooling Fan:
P0493 Fan Over-speed
P0495 Fan High Speed
Symptoms
Symptoms of a P0494 engine code may include:
Engine overheating
Engine noises
Poor performance
Engine misfire
Stalling
Poor fuel consumption
Potential Causes
Typically, the causes for this code to set are:
Broken or damaged wiring harness
Faulty fan clutch
Faulty cooling fan clutch or bearing
Faulty cooling fan relay
ECM problem
Pin/connector issue (e.g., corrosion)
Diagnostic and Repair Procedures
Whenever working with electrical systems, some basic tools that are a good idea are:
OBD code reader
Multimeter
Basic socket set
Ratchet and wrench sets
Basic screwdriver set
Rags/shop towels
Battery terminal cleaner
Service manual
Safety Tips
Let the engine cool down
Chock the wheels
Wear PPE (Personal Protective Equipment)
Basic Step #1
Visual Inspection. First, you’ll want to open the hood and locate your radiator/fan assembly. Most of the time, it will be mounted towards the front of the vehicle, directly in front of the engine. Keep in mind there are many different styles and configurations for cooling fans; some are mounted directly on the radiator itself, and some are belt-driven by the engine, so identify the style of your particular cooling fan. Once located, inspect the fan(s) and blades for any damage. It’s a good idea to grab one of the fan blades and shake it gently to check for any play in the bearings; depending on the style and the amount of play present, you may need to replace the fan. Also, be sure to inspect the shroud and anything that could hinder fan performance. Pay close attention to the cooling fan wiring harness. It only takes one slightly frayed wire to trigger certain codes. If everything is okay, proceed.
TIP: Sometimes aftermarket shrouds don’t fit perfectly, causing the fan to rub on parts of the shroud, leading to low speed. Spin the fan by hand with the engine off and cold. The fan should spin freely within the shroud (it may be necessary to remove the belt for the belt-driven version).
Basic Step #2
Check the Connector. First, ensure the battery is disconnected before performing any repairs or tests on the electrical system. Follow the wiring harness coming from the cooling fan until you find its connector. Once located, inspect for overheating/melting or corrosion. Disconnect it and inspect the pins inside. Any corroded or bent pins should be repaired/replaced. Generally, any damage to the connector means you’ll need to replace it. If everything is okay, proceed.
TIP: Ensure you have a healthy electrical system. Always be aware that if you have a weak battery or an issue with your charging system, the ECM may falsely illuminate the check engine light among many other possibilities.
Basic Step #3
Check the Relay. Depending on your system, you may have a cooling fan relay that helps control your fan. Refer to the manufacturer for the location. If the relay appears melted or burnt, this could indicate a problem with the relay and it should be replaced.
TIP: It’s a good idea to purchase these types of relays from your dealer, as I have found faulty aftermarket relays that caused serious damage.
Basic Step #4
Check your ECM or PCM. Locate your ECM. The location heavily depends on the make and model, but you might find an ECM: under a seat, under the hood, in the trunk, mounted on the firewall, under the dashboard, in a fender, or floor-mounted somewhere. Once located, inspect for water damage or corrosion; this could indicate a problem. Skilled expertise would be needed beyond this point.