What P0198 means
The engine oil temperature sensor A is an NTC thermistor fed with 5 V through a resistor: the hotter the oil, the lower the signal voltage.
How the engine computer detects it
The engine module uses the oil temperature for variable cam timing (Ford disables it with cold oil or a sensor fault), engine protection and the oil life monitor; many engines have no such sensor and use a calculated oil temperature instead. P0198 means the signal sits near the 5 V reference, so the module sees extremely cold oil (below −40 °C (−40 °F)) – typically an unplugged connector, a broken wire, an open sensor element or a short to voltage. Ford sets it above 4.93–4.96 V for 5 s; GM above 450 kΩ, enabled only after 20 s of running or above −20 °C (−4 °F) coolant so that real extreme cold is not mistaken for a fault; no MIL on the 2018 LT4, two trips in 2019. The module uses a substitute value and Ford disables variable cam timing.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on (depending on manufacturer)
- Oil temperature display stays at minimum or blank
- Restricted cam timing, possibly slightly less power
- Oil life monitor calculates with a substitute value
Common causes
- Connector unplugged or pins corroded, signal or ground wire broken Most likely
- Sensor element open Possible
- Signal wire shorted to 5 V or battery voltage Less likely
- Control module pull-up or input faulty Less likely
How to diagnose P0198
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: engine oil temperature sensor, sensor wiring.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 1
- Fuel and air metering
- 98
- Specific fault
Questions drivers ask
Can I drive with code P0198?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P0198?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0198 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0198 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.