P0198Engine Oil Temperature Sensor A Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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. 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) – 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 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.
- What you may notice
- 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
- Likely causes
- LikelyConnector unplugged or pins corroded, signal or ground wire broken
- PossibleSensor element open
- RareSignal wire shorted to 5 V or battery voltage
- RareControl module pull-up or input faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €30 – €200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.