Technical Description of OBD-II Trouble Code
Intermittent Circuit Issue with Engine Coolant Temperature Sensor
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to all vehicles manufactured from 1996 onwards (Ford, Hyundai, Kia, Mazda, Mercedes-Benz, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
When I connect my code reader to a vehicle and find a stored P0119, I understand that the powertrain control module (PCM) has detected an intermittent signal from the engine coolant temperature (ECT) sensor.
The PCM monitors the ECT using a reference circuit (typically five volts) that is completed by the ECT sensor. If separate ECT sensors are used (one for the PCM and another for the temperature gauge), the sensor is usually designed with two wires. The first wire carries the five-volt reference, and the second wire serves as the ground wire. The ECT sensor is typically a negative coefficient sensor, meaning that as the sensor temperature increases, the resistance decreases. The variation in sensor resistance results in fluctuations in circuit voltage, which the PCM recognizes as changes in ECT. If the PCM and the temperature gauge use the same ECT sensor, then the sensor will have three wires. It responds to temperature in the same way as the two-wire sensor, but one wire provides an input signal to the gauge, and the other wire provides an input signal to the PCM. Pretty simple, right?
Although the location of the ECT may vary among manufacturers, it is always threaded directly into an engine coolant passage. Many automakers place the ECT sensor in the cylinder block or cylinder head, while others thread it into one of the intake manifold coolant passages, and some locate it in the thermostat housing.
With the ECT sensor threaded into the engine, the tip of the sensor, which contains the thermistor, extends into the coolant passage. With the engine running, coolant should continuously flow across the tip. As the engine coolant temperature increases, so does the thermistor inside the ECT sensor.
The PCM uses the engine temperature to calculate fuel delivery, idle speed, and ignition timing. The input from the ECT sensor is crucial because the engine control system must operate differently as the engine temperature changes from ambient temperature to over 220 degrees Fahrenheit. The PCM also uses the ECT sensor input to activate the electric cooling fan.
If the PCM receives erratic or intermittent input signals from the ECT sensor within a specific period of time and under certain circumstances, it will store a code P0119 and may illuminate the malfunction indicator lamp (MIL).
An example of an Engine Coolant Temperature ECT sensor
Severity & Symptoms
Due to the significant role of the ECT sensor in engine drivability, it is important to address the code P0119 urgently.
Symptoms of a P0119 code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) specific to your vehicle. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
When faced with diagnosing a code P0119, I recommend having a suitable diagnostic scanner, a digital volt/ohmmeter (DVOM), an infrared thermometer, and a reliable source of vehicle information (such as All Data DIY) on hand.
I prefer to connect the scanner to the vehicle diagnostic connector, retrieve stored trouble codes and freeze frame data, and write down this information to begin my diagnosis. Then, I clear the codes.
Next, I would visually inspect the ECT sensor wiring and connectors. I would repair or replace any burnt or damaged wiring and/or connectors as necessary and retest the system. If the P0119 code is not immediately reset, it may be intermittent. I would operate the vehicle normally until the PCM enters OBD-II readiness mode or the code is reset. If the P0119 code is now reset, I would continue with the diagnosis.
I would reconnect the scanner and display the appropriate data stream. I would narrow down the data stream to show only relevant data, which would result in faster data response. While observing the ECT sensor temperature and voltage, I would look for glitches or inconsistencies. The PCM interprets these as intermittent ECT sensor circuit signals. If there are inconsistencies, I would inspect the ECT sensor connector for signs of corrosion. I would also check the wiring that is routed near hot exhaust manifolds/headers (potential intermittent short to ground) and inspect the ECT sensor for loose or broken connector pins. I would repair or replace any defective components as necessary.
A low engine coolant level may also contribute to the storage of a code P0119. With the engine cool, I would remove the high-pressure cap and ensure that the engine is filled with the recommended coolant. If the engine coolant level is more than a few quarts below the recommended level, I would inspect the engine for a coolant leak. A cooling system pressure tester may be useful for this task. I would repair any leaks as necessary, refill the system with suitable coolant, and retest the system.
If the ECT sensor is observed (in the scanner data stream display) as being extremely low or high, it is likely defective. Using the DVOM, I would test the ECT sensor resistance and compare the findings with the manufacturer’s recommendations. If the sensor fails to comply, I would replace it.
If the ECT sensor appears slightly low or high, I would use the infrared thermometer to measure the actual ECT. I would compare the ECT sensor signal reflected in the data stream with the actual ECT and discard the sensor if the two do not match.
Additional diagnostic notes:
Other ECT sensor diagnostic codes include P0115, P0116, P0117, and P0118.
