Fault code P2186 – engine coolant temperature sensor 2 circuit intermittent/erratic

Fault code P2186 is called “Engine Coolant Temperature (ECT) Sensor 2 Circuit Intermittent/Erratic” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P2186

An intermittent signal in the coolant temperature circuit will cause an OBD-II code P2186. This occurs when the PCM detects a voltage or resistance value that deviates or interrupts in either direction from the design parameters. The deviation should be approximately 10% over a period of time.

Fault code P2186 – engine coolant temperature sensor 2 circuit intermittent/erratic

The temperature sensors on modern engines are of the variable resistance type, which convert temperature into signal voltages. The colder the engine coolant, the higher the resistance. As the coolant temperature increases, the resistance decreases, thereby increasing the signal voltage to the PCM.

It is rare for an engine to have only one coolant temperature sensor. In most cases, one sensor is used to control the thermometer. The other controls the electric radiator fan or the cold start valves in some older systems.

Some diesel engines may have a special coolant temperature sensor to control the glow plugs.

As a result, when the coolant temperature changes, the resistance changes and the PCM sees this. When the engine is cold, the resistance is high. When the engine is warm, the resistance is low. If the PCM detects a voltage condition that is transmitted with an interruption, error P2186 will be set.

Symptoms of vehicle malfunctions

The main signal that an error P2186 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine control lamp on the control panel will light up (the code will be recorded in the ECM memory as a malfunction).
  2. Engine stalls or starts poorly (especially when starting cold).
  3. Floating revolutions, as well as attempts to stall at idle.
  4. Overheating of the engine.
  5. Black smoke from the exhaust pipe, when working with a rich mixture.
  6. Increased NOx emissions may be observed on a lean mixture.
  7. Abnormal operation of the cooling fans.

Error P2186 is not serious, the car will be able to start and continue driving. But it’s better to solve it as soon as possible, because improper heat exchange can lead to more serious consequences.

Factors that can cause this error code

The error code P2186 can mean that one or more of the following problems have occurred:

  • ECT sensor has failed.
  • Coolant temperature sensor circuit is broken.
  • Coolant temperature sensor wiring harness or connector is damaged.
  • Engine coolant level is low.
  • Engine coolant thermostat does not open at proper temperature.
  • Sometimes the cause is a defective PCM module.

How to fix or reset OBD-2 code P2186

Some suggested steps for troubleshooting and fix the error code P2186:

  1. Read all stored data and error codes with an OBD-II scan tool. To find out when and under what circumstances error P2186 appeared.
  2. Clear the error codes from the computer memory and test-drive the vehicle to find out if the error appears again.
  3. Check the coolant level (engine should be cold).
  4. Visually inspect the electrical wiring and connections to the sensor for looseness and damage. Repair if necessary.
  5. If the ECT sensor has failed, replace it.
  6. Test the thermostat; if it has failed, replace it.
  7. Clear the error code from the computer memory again, test drive the vehicle to see if the problem is resolved.

Diagnose and repair of problems

The first step in troubleshooting error P2186, is to review the Technical Service Bulletins (TSB). For known problems with a particular vehicle.

Perform a thorough visual inspection to check the wiring for obvious defects such as scratches, scuffs, exposed wires or burn spots. Next, check connectors and connections for safety, corrosion, and contact damage.

Be sure to carefully check the integrity of the wire harnesses and secure any loose wires. If you find a burned wire, solder it and make sure it is properly insulated.

Check coolant and thermostat

Make sure the coolant level is correct, both in the radiator (when cold) and in the coolant overflow tank. Make sure that there are no leaks and that the sealed cap is working properly.

If there is not enough coolant in the system, the engine may not warm up properly. Because if the temperature sensor is not in contact with the coolant, it will not read the temperature.

Using a non-contact thermometer, or a real-time streaming scan tool, check to see if the engine is warming up properly. Normally, the upper radiator hose should stay relatively cold until the thermostat opens. After that, it will warm up quickly.

If the thermostat is open, the coolant will leak constantly, preventing the engine from reaching operating temperature. This can also be the cause of fault code P2186.

Use a thermometer or diagnostic tool to check the engine temperature after 10-15 minutes of operation. If the temperature does not reach the operating temperature, check the ECT sensor.

Check the coolant temperature sensor (ECT)

Visually check the sensor for wiring or connector damage and repair if necessary. Then connect an OBD2 scanner, if the engine temperature is excessively high, about 284°F, this is not normal.

Disconnect the sensor on the engine and see if the reading drops, like 50°F. If it does, the sensor is probably faulty, shorted internally, causing a low resistance signal to be sent to the PCM.

But, if you want to be completely sure it’s the sensor and not the wiring, you can do a test. Check the resistance of the sensor against ground with an ohmmeter. The resistance of a normal sensor will vary slightly from car to car.

But basically, if the engine temperature is about 200 degrees Fahrenheit, the resistance will be about 200 ohms. At about 0°F, the resistance will be over 10,000 ohms.

You can use this test to determine if the resistance of the sensor matches your engine temperature. If it doesn’t match your engine temperature, you probably have a faulty sensor.

On which vehicles does this problem occur most frequently

Fault code P2186 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Chevrolet
  • Ford
  • Hyundai
  • Kia
  • Mazda (6)
  • Mercedes-Benz
  • Porsche (Panamera)
  • UAZ
  • VAZ

Fault code P2186 can sometimes be found with other errors. The most common are the following: P0115, P0116, P0117, P0118, P0119, P0125, P0128, P2182, P2183, P2184, P2185.


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