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P0198 Engine Oil Temperature Sensor High

OBD-II Trouble Code Technical Description

Article by
Mia B.
ASE Certified Master Technician

Engine Oil Temperature Sensor High

What does that mean?

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles that have an engine oil temperature sensor (Ford Powerstroke, Chevrolet GMC Duramax, VW, Nissan, Dodge, Jeep, Audi, etc.). Although generic, the exact repair steps may vary depending on make/model.

The engine oil temperature (EOT) sensor produces a signal that is used by the powertrain control module (PCM) 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 often found in diesel applications.

EOT sensors receive a reference voltage (usually 5 volts) from the PCM. They then vary their internal resistance in relation to engine oil temperature to send a return voltage signal to the PCM. EOT sensors are a type of negative temperature coefficient (NTC) thermistor. This means internal resistance of the sensor is inversely proportional to the oil temperature. The EOT sensor signal voltage goes down when the engine oil temperature goes up and vice versa.

Code P0198 is set when the PCM detects a high engine oil temperature sensor signal. This usually indicates an open circuit.

A typical engine oil temperature sensor:
Engine Oil Temperature Sensor

Related engine oil temperature sensor trouble codes include:

Code Severity & Symptoms

The severity of these codes is moderate to severe. In some cases, these codes set along with coolant temperature codes, can indicate an engine overheat condition. It’s a good idea to address this code as soon as possible.

Symptoms of a P0198 engine code may include:


Possible causes for this P0198 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 damage is found, repair as necessary, clear the code and see if it returns.

Next, check for technical service bulletins (TSBs) regarding the issue. If nothing is found, you will need to move forward to step by step diagnosis of the system.

The following is a generalized procedure, as testing for this code varies between vehicles. To accurately test the system, you'll want to refer to the manufacture’s diagnostic flow chart.

Check for proper cooling system operation: Check that the engine reaches and maintains a proper operating temperature. If the engine overheats or does not warm up as designed, there is a problem with the cooling system that should be addressed prior to any further testing. Cooling system DTCs being set along with an engine oil temperature sensor DTC, also indicate a potential problem with the cooling system.

Do some 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, the connections are sound and the ECM can recognize the input. This means the problem is most like the sensor and not a circuit or PCM problem.

Test the sensor: Disconnect the engine oil temperature sensor connector. Next, measure the resistance between the two sensor terminals using a digital multimeter set to ohms. Start the engine and watch the meter value; the values should decrease smoothly as the engine warms up (check the engine temperature gauge on the dash to ensure the engine reaches operating temperature). If engine temperature increases but EOT resistance does not decrease, the sensor is faulty and should be replaced. Note: most manufactures have resistance/temperature charts in their service information to aid in the diagnostic process.

Check the circuit:

Related P0198 DTC Discussions

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