P2186 # 2 Coolant Temperature Sensor Circuit Malfunction

P2186 # 2 Coolant Temperature Sensor Circuit Malfunction

OBD-II DTC Datasheet

Malfunction of the coolant temperature sensor circuit No. 2

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to all vehicles since 1996 (Ford, Hyundai, Kia, Mazda, Mercedes-Benz, etc.). Although general in nature, the specific repair steps may differ depending on the brand / model.

When I connect my code reader to the vehicle and find the stored P2186, I know that the powertrain control module (PCM) has detected an intermittent signal from the # 2 engine coolant temperature (ECT) sensor.

The PCM controls the ECT sensors using a reference circuit (usually five volts) that is terminated by the ECT sensor. If separate ECT sensors are used (one for the PCM and one for the temperature sensor), the sensor itself is usually a two-wire design. The first wire carries the XNUMXV reference voltage and the second wire is the ground wire. An ECT sensor is usually a negative coefficient sensor, which means that as the temperature of the sensor increases, the resistance decreases. A change in sensor resistance results in voltage fluctuations in the circuit, which the PCM recognizes as changes in ECT. If the PCM and temperature sensor use the same ECT sensor, then the sensor will be XNUMX-wire. It responds to temperature in the same way as a two-wire sensor, but one wire provides input to the sensor and the other wire passes the input to the PCM. It's simple, right?

Although the location of the ECT will vary from manufacturer to manufacturer, it will always be inserted directly into the engine coolant channel. Many automakers place an ECT sensor in the cylinder block or cylinder head, others screw it into one of the intake manifold coolant passages, and some place it in the thermostat housing.

When the ECT sensor is screwed into the engine, the tip of the sensor, which contains the thermistor, protrudes into the coolant channel. With the engine running, coolant must constantly flow through the tip. As the engine coolant temperature increases, so does the thermistor inside the ECT sensor.

The PCM uses engine temperature to calculate fuel delivery, idle speed, and ignition timing. The ECT sensor input is critical because the engine management system must operate differently as the engine temperature changes from ambient temperature to more than 220 degrees Fahrenheit. The PCM also uses the ECT sensor input to turn on the electric cooling fan.

If the PCM receives input signals from ECT sensor # 2 that are erratic or intermittent for a set period of time and under certain circumstances, code P2186 will be stored and a malfunction indicator lamp (MIL) may illuminate.

Example of an ECT engine coolant temperature sensor

Note. This DTC is basically the same as P0119, however the difference with this DTC is that it relates to ECT # 2 sensor circuit. Therefore, vehicles with this code mean they have two ECT sensors. Make sure you are diagnosing the correct sensor circuit.

Severity and symptoms

Because the ECT sensor plays such an important role in engine handling, the P2186 code needs to be urgently addressed.

Symptoms of a P2186 code may include:

• Rough engine idling during cold start
• Hesitation or stumbling when accelerating
• Strong exhaust odor, especially during cold start
• Engine overheating possible
• The cooling fan runs continuously or does not work at all

reasons

Possible causes of this engine code include:

• Low engine coolant level
• Faulty thermostat
• Defective sensor # 2 ECT
• Open or short circuit of the wiring and / or connectors in the sensor circuit No. 2 ECT

Diagnostic and repair procedures

A good starting point is always to check the Technical Service Bulletins (TSB) for your particular vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

When faced with a P2186 code diagnosis, I like to have a suitable diagnostic scanner, digital volt / ohmmeter (DVOM), infrared thermometer, and a reliable source of vehicle information (such as All Data DIY) on hand.

I like to connect the scanner to the vehicle diagnostic socket, retrieve stored DTCs and freeze frame data, and write this information down to start diagnostics. Now clear the codes.

Then I would do a visual inspection of the wiring and connectors of the ECT # 2 sensor. Repair or replace burnt or damaged wiring and / or connectors as needed and retest the system. If P2186 is not reset immediately, it may be intermittent. Drive normally until the PCM enters OBD-II ready mode or the code is cleared. If P2186 is reset, continue diagnostics.

Reconnect the scanner and invoke the appropriate data stream. Narrow down the data stream so that only relevant data is displayed and the data response is much faster. Observe the temperature and voltage of the ECT # 2 sensor for malfunctions or inconsistencies. This will be perceived by the PCM as an intermittent signal from the ECT sensor circuit. If there is a discrepancy, inspect the ECT sensor connector for corrosion. Check wiring near hot exhaust manifolds / manifolds (intermittent short to ground) and loose or broken connector pins on the coolant temperature sensor. Repair or replace defective components as necessary.

A low engine coolant level may also contribute to a P2186 code. When the engine has cooled, remove the high pressure cap and make sure the engine is filled with the recommended coolant. If the engine coolant level has dropped by more than a few quarts, check the engine for coolant leaks. A pressure gauge in the cooling system can be useful for this. Repair the leaks if necessary, fill the system with a suitable coolant and recheck the system.

If the # 2 ECT sensor is detected (on the scanner's data flow display) as being too low or high, suspect it is defective. Using the DVOM, check the resistance of the ECT sensor and compare your results with the manufacturer's recommendations. Replace the sensor if it does not meet the requirements.

If ECT # 2 sensor seems a little low or high, use an infrared thermometer to get the actual ECT. Compare the ECT sensor signal reflected in the data stream with the actual ECT and discard the sensor if they do not match.

Additional diagnostic notes:

• Before attempting to diagnose a P2186, make sure the engine is filled with coolant and the thermostat is working properly.
• Other ECT sensor codes as well as engine overtemperature codes may accompany this type of code.
• Diagnose and repair other ECT related codes before diagnosing P2186.

Corresponding ECT sensor circuit codes: P0115, P0116, P0117, P0118, P0119, P0125, P0128, P2182, P2183, P2184, P2185

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