Error Code P0485 is defined as Cooling Fan Power/Ground Circuit Malfunction.

This code is a generic trouble code, which means it applies to all vehicles equipped with an OBD-II scanner, or vehicles made since 1996 up to present. It is, however, more common among Mazda and Mercedes Benz vehicles. Specifications on the definition, troubleshooting and repairs, of course, vary from one make/model to another.


Typically found mounted behind the radiator and in front of the engine, the Cooling Fan Module is controlled by the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes), which is based upon the inputs wired to it.

The PCM uses these inputs through voltage signal to determine engine coolant and intake air temperature, air conditioner pressures, and vehicle speed. When the PCM detects that the reading from the electric cooling fan control circuit is either too low or too high in comparison to the specifications set by the manufacturer, the Error Code P0485 is set.

Error Code P0485 is set when there is an abnormal voltage detected during normal fan operation on the power side/ground side of the cooling fan circuit. This can happen during low, medium, or high-speed operation. This also includes vehicles using fan relay to run the cooling fans. Unlike most related cooling fan codes, this code is only concerned with the electrical issues (failed cooling fan circuit), and intermittent problems. Of course, the procedure of troubleshooting depends upon the manufacturer, type of cooling fan module, and wire colors.

Other related cooling fan trouble codes include:

Common Symptoms

Symptoms of this code depend on the severity of the condition. If the problem is caused by a mechanical failure, then it may not be as severe, and the PCM can compensate for the problem, as long as the engine does not overheat. As the PCM compensates, the temperature gauge must be monitored during all driving cycles. Typically, the fan runs all the time (100% duty cycle).

As with other error codes, of course, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms of this code include:

  • Engine overheating
  • Malfunctioning A/C system
  • Blown fuses

Possible Causes

In most cases, this code is caused by a malfunctioning cooling fan motor, or defective fan control relay. Other possible causes include:

  • Faulty cooling fan module
  • Open or short to power on the fan control circuit between the PCM and the cooling fan module
  • Short to ground on the fan control circuit to the cooling fan module
  • Defective PCM (rare)

How to Check

It’s always a good idea to check the TSB (Technical Service Bulletin) of the particular vehicle before diagnosing this code. The vehicle may have or need a PCM flash/reprogram to cover the problem.

Typically, diagnosis for this code starts with a visual inspection of the connectors and wirings between the PCM and the cooling fan. If anything appears damaged, corroded, loose, or faulty, then repair or replace these components before clearing the codes and retesting the system.

If the error code returns, then technicians usually proceed on other repair options.

Connect the scan tool, clear the codes from the memory, and see if the code returns. If it does NOT return, then the problem is in the connections.

If the code does return, then check the integrity of the cooling system. Make sure both the water pump and thermostat are running properly. When the engine is cooled, remove the radiator cap and make sure it’s properly sealed. If there are questions about these cooling components, then they must be replaced first, as they’re usually the cause of this code. After replacing, clear the code and check if the code returns.

If the code returns, then you must check the fan and its associated circuits. Usually, there are 2 wires at each cooling fan in the module. Disconnect the harness that goes to the cooling fan module first. Using the DVOM (digital volt/ohmmeter), connect one lead of the meter to one terminal of one of the fans. Then, connect the remaining meter lead to the other fan terminal. This should not be open or shorted. Make sure you verify the specifications of the resistance for your particular vehicle model. If the motor of the fan is either open or shorted (infinite resistance or no resistance/ 0 ohms) then replace the cooling fan module or if applicable, the cooling fan motor.

If it passes the DVOM test, for 12V in the cooling fan module power supply circuit (Red lead to the fan power supply circuit, black lead to a good ground). Next, if your scan tool can activate the cooling fans, turn the cooling fans on. If there is no 12V in the fan, repair the wiring from the PCM or relay to the fan, or possibly a bad PCM.

If it’s ok, then check the cooling fan module, make sure there’s a good ground. Connect a test light 12V battery positive (red terminal) and touch the end of the test light on the ground circuit that goes to the cooling fan circuit ground. Use the scan tool to actuate the cooling fan module and check if it lights up each time the scan tool actuates the fan. If it does NOT light up, then you may have a problem with the circuit. If it DOES light up, then wiggle the wiring harness to check for intermittent connection. If the light flickers, then that suggests an intermittent problem.

If the vehicle passed all tests and you still get the code, then this would mean a failed cooling fan module, though defective PCM must not be ruled out as well.

PCM must be programmed, or calibrated to be installed correctly.

How to Fix

The easiest and most obvious fix for this code is replacing the cooling fan. The fan must be disconnected from the power and all other hardware that connects to it, even those hardware that keeps you from reaching the fan housing.

Make sure you do it gently and do not damage the fan housing in the process, as well as other components.

Put the unit on a flat surface and then remove the fan blade from the by releasing the screw or pin that holds it in place. Then release the motor from the housing. Test your work by turning the vehicle on and setting the air conditioner at max setting. Then, observe how the fan is working.


Error P0485 code is a serious problem and demands immediate attention. Unless you are very skilled and have the proper tools, you’re better off leaving this problem to a professional technician.

Replacing the fan may be easy, but you need to have the right tools to do it right. If unsure, don’t hesitate to ask for professional help.