What does it mean?
If the engine is the heart of your vehicle, then engine oil is the blood. Without engine oil to lubricate hundreds of moving metal parts, some of them separated by less than the width of a human hair, your engine would quickly overheat and weld itself into a useless chunk of metal. Engine oil, aside from lubrication, is also the principal manner in which heat is removed from the engine, which is why some oil pans have cooling fins and some engines are equipped with oil coolers.
Some applications, such as towing or racing, require the installation of auxiliary oil coolers to maintain proper lubrication, cooling, and engine function. Engine Oil Temperature and Pressure Oil temperature is important because excessive temperature could lead to burning, engine overheating, and loss of lubrication. The engine control module (ECM) uses the engine oil temperature (EOT) sensor to monitor oil temperature.
The EOT signal is also utilized by the instrument cluster if the vehicle is equipped with an oil temperature gauge or oil temperature warning light. If the ECM detects a problem with the EOT signal, it will set a diagnostic trouble code (DTC) in system memory and illuminate the malfunction indicator lamp (MIL).
For example, if the engine has been off for a few hours at engine startup, the ECM assumes that the EOT should measure about the same as the IAT and ECT (intake air temperature and engine coolant temperature) sensors. If EOT readings are off by more than a few degrees, the ECM assumes a fault in the EOT or its circuit. After the engine has started, it monitors EOT and estimates how warm the oil should be heating up within a certain amount of time.
If measured oil temperature doesn’t rise above a certain threshold within that time limit, the ECM assumes a fault. DTC P0198 is defined as “Engine Oil Temperature (EOT) Sensor High Input Error.”