P0197Engine Oil Temperature Sensor A Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- 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. P0197 means the signal voltage is below its lower limit, so the module would read implausibly hot oil (around 145–150 °C) – practically always a signal wire shorted to ground or an internally shorted sensor. Ford sets it below 0.16–0.20 V for 5 s; GM below 25 Ω in 20 of 50 samples – without a warning light on the 2018 LT4, with two trips on the 2019 version, so MIL behaviour depends on the manufacturer and model year. A substitute value is used.
- What you may notice
- Check engine light on (depending on manufacturer)
- Oil temperature display at maximum or oil temperature warning
- Fan running constantly or power reduction possible
- Restricted cam timing (Ford)
- Likely causes
- LikelySignal wire chafed against ground or the engine block
- PossibleSensor shorted internally
- PossibleOil or water in the connector (leakage current)
- RareControl module 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.