Technical Description of OBD-II Trouble Code
Intermittent Engine Oil Temperature Sensor
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to OBD-II equipped vehicles with an engine oil temperature sensor (such as Ford Powerstroke, Chevrolet GMC Duramax, VW, Nissan, Dodge, Jeep, Audi, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The engine oil temperature (EOT) sensor generates a signal that the powertrain control module (PCM) uses to calculate fuel quality, injection timing, and glow plug operation. The EOT signal is also compared to other temperature sensors, such as the intake air temperature (IAT) sensor and engine coolant temperature (ECT) sensor, for diagnostic purposes. EOT sensors are commonly found in diesel applications.
EOT sensors receive a reference voltage (typically 5 volts) from the PCM. They then adjust their internal resistance based on the engine oil temperature to send a return voltage signal to the PCM. EOT sensors are a type of negative temperature coefficient (NTC) thermistor, meaning that the internal resistance of the sensor is inversely proportional to the oil temperature. The EOT sensor signal voltage decreases as the engine oil temperature increases, and vice versa.
A typical engine oil temperature sensor:
Code P0199 is triggered when the PCM detects an intermittent issue with the engine oil temperature sensor signal.
Related trouble codes for the engine oil temperature sensor include:
Code Severity & Symptoms
The severity of these codes ranges from moderate to severe. In some cases, when these codes are accompanied by coolant temperature codes, they can indicate an engine overheat condition. It is advisable to address this code as soon as possible.
Symptoms of a P0199 engine code may include:
Causes
Possible causes for this P0199 code include:
Diagnostic and Repair Procedures
Begin by visually inspecting the engine oil temperature sensor and the corresponding wiring. Look for loose connections, damaged wiring, etc. If any damage is found, repair it as necessary, clear the code, and check if it reappears.
Next, check for any technical service bulletins (TSBs) related to the issue. If no relevant information is found, proceed with step-by-step diagnosis of the system.
The following is a general procedure, as the testing for this code varies between vehicles. To accurately test the system, refer to the manufacturer’s diagnostic flow chart.
Check for proper cooling system operation: Ensure that the engine reaches and maintains the proper operating temperature. If the engine overheats or fails to warm up as intended, there may be a problem with the cooling system that should be addressed before further testing. The presence of cooling system DTCs along with an engine oil temperature sensor DTC also indicates a potential issue with the cooling system.
Perform preliminary circuit testing: Use a scan tool to monitor the engine oil temperature sensor data parameter. Disconnect the EOT sensor; the scan tool value should drop to a very low value. Next, connect a jumper wire across the terminals. If the scan tool now displays a very high temperature, it indicates that the connections are sound and the ECM can recognize the input. This suggests that the problem is most likely with the sensor itself rather than a circuit or PCM problem.
Test the sensor: Disconnect the engine oil temperature sensor connector. Then, measure the resistance between the two sensor terminals using a digital multimeter set to ohms. Start the engine and observe the meter value; the values should decrease smoothly as the engine warms up (check the engine temperature gauge on the dashboard to ensure that the engine reaches the operating temperature). If the engine temperature increases but the EOT resistance does not decrease, it indicates that the sensor is faulty and should be replaced. Note: most manufacturers provide resistance/temperature charts in their service information to assist in the diagnostic process.
Check the circuit:
