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Error Code P0495 is referred as Fan Speed High. It means the PCM has detected an incorrect voltage (too high or too low) in the electric cooling fan control circuit.
Crankshaft sensor signals the ignition control or the fuel injection computer when the cylinders are firing. This will cause the ignition coil to provide the spark, and the injector to inject fuel into each cylinder at the perfect time. If either of these components is working properly, the vehicle will start to run tough due to the engine being less efficient. For later vehicle models, the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) can usually allow the vehicle to run, with the Check Engine light on the dashboard.
Variations on voltage that goes more than 10% of the specified voltage range by the manufacturer will cause a code to be stored and illuminate the Check Engine light. Some vehicles may even require multiple drive cycles (around three) for the Service Engine Soon (Check Engine) lamp to light up. If there’s no Check Engine light but the code is still stored, that would mean the code may be displayed as a pending code.
Symptoms for Error Code P0495 are usually limited to the Check Engine light and the stored codes. For some cases however, it may also include overheating of the engine when the vehicle is at stop, as well as reduced efficiency of the air conditioner.
The most common cause for this error code is bad cooling fan motor or faulty cooling fan relay. In rare cases, it can possibly be caused by loose or corroded electrical connectors, faulty engine coolant temperature sensor or open or shorted electrical wiring which is often results in a blown fuse.
How to Check
As with other trouble codes, diagnosis for P0495 require a scanner (code reader) and a DVOM (digital volt-ohmmeter). Mechanics conduct a visual inspection of all the connectors and wirings involved in the component, along with the hoses and vacuum lines.
If all system wirings, connectors and components (especially fuses) appear to be in normal working condition, technicians connect the scanner to the diagnostic connector to record the stored codes and freeze frame data.
This information is important to determine the conditions that cause the intermittent issues that may contribute to the code being stored. They will then clear the codes and take the vehicle for a test drive to see if they return. If the code don’t return, then the condition is intermittent, which can be quite a challenge to diagnose, and in extreme cases, the problem may be allowed to worsen before one can make the right diagnosis.
The scanner will be used to activate the engine cooling fan and to carefully perform quick test for both voltage and ground (battery voltage is normal) at the cooling fan motor. Technicians may successfully determine whether the fan motor is at faulty, or if it’s a case of lack of voltage or ground. If there are no voltage present from the primary cooling fan, technicians will then start testing the system fuses.
If the fuses are in good condition, technicians will then look for the engine cooling fan relay and compare the voltage readings at the connector from the specifications provided by the manufacturer for the operation of the fan. Shorted circuits and damaged fuses and relays must be repaired, if not replaced.
If there is no output signal present from the PCM, then the technician will connect a scanner to observe the engine temperature. If the reading is within the specifications of the manufacturer, that could mean a faulty engine coolant temperature sensor.
The sensors are tested by comparing actual temperature to resistance values with the manufacturer’s specified temperature to resistance values. If the temperature fails to coincide, then that means the engine coolant temperature sensor must be replaced.
To check for open or shorted wiring on the electrical connectors in the cooling fan circuit, engine coolant temperature sensor is disconnected and checked whether it yields to no change in the temperature reading from the scanner.
Before checking for resistance, technicians disconnect the PCM connector and compare the findings from the specifications provided by the manufacturer.
In rare cases, the problem can be caused by a faulty PCM.
How to Fix
For fan noise issue, test the fan clutch by bringing the vehicle to its operating temperature. Then, disconnect the cooling fan relay at the under-hood junction block. Or you can disconnect the connector of the cooling fan harness. Next, run the engine in park at 2,000RPM for 2 minutes. If the cooling fan roars, that means you have a bad electric fan clutch (a very common issue) and must be replaced.
Other issues such as faulty, corroded or loose wires, hoses and connectors must be repaired, if not replaced, as necessary.
It is crucial to perform a thorough and correct diagnosis of this error code before replacing any components, such as the cooling fan motors.
Replacing the fan clutch may be expensive, but it is necessary, as it can cause tearing from the bearing of the water pump, which will be flowed by belt and plastic shroud housing.