Faulty engine oil temperature sensor reading out of range; Open circuit in the sensor signal or ground wire, or a poor ground connection; Corroded, loose or damaged sensor connector terminals; Signal wire shorted to a voltage supply; Chafed or damaged wiring harness near hot or moving components; Fault inside the engine control unit.

P0198

Engine Oil Temperature Sensor A Circuit High.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
98: FaultThe specific fault in that area

What it means

P0198 means the engine control unit has detected the signal from the engine oil temperature sensor is higher than expected, which equates to a voltage that is too high for a sensor circuit. This usually points to an open circuit, a short to voltage or a faulty sensor, rather than genuinely hot oil. The code sets when the signal sits outside the plausible range for long enough during the monitoring period.

Symptoms

Engine warning light on
Oil temperature gauge or display reading incorrectly, stuck at maximum or showing no reading
Reduced performance or the engine running in a default (limp) mode on some models
Variable valve timing or oil-temperature-dependent functions behaving oddly
Slightly poorer fuel economy or rough running on cold starts, depending on how the control unit uses the signal

Possible causes

Faulty engine oil temperature sensor reading out of rangelikely
Open circuit in the sensor signal or ground wire, or a poor ground connectionlikely
Corroded, loose or damaged sensor connector terminalslikely
Signal wire shorted to a voltage supplypossible
Chafed or damaged wiring harness near hot or moving componentspossible
Fault inside the engine control unitrare

How to diagnose

Read the stored codes and freeze frame data, then note any other temperature sensor codes that might suggest a shared ground or supply fault.
Compare the live oil temperature reading with coolant temperature on a cold engine; they should be close, and a reading stuck at the extreme high or low end suggests a circuit fault.
Inspect the sensor, connector and harness for oil contamination, corrosion, bent pins, chafing and heat damage.
With the ignition on, unplug the sensor and watch the live reading, then bridge the signal and ground terminals at the connector as the model's wiring diagram allows, to see whether the reading changes as expected.
Measure the reference voltage and ground at the sensor connector against the manufacturer's specification for that engine.
Check the sensor resistance at a known temperature against the manufacturer's data.
Test the signal wire for continuity back to the control unit and for a short to voltage, with the battery disconnected where appropriate.
If the wiring and sensor test fine, check for water ingress or damage at the control unit connector and consult model-specific guidance before suspecting the control unit.

How to fix

Replace the oil temperature sensor if its resistance or signal is out of specification, using the correct seal or washer for that engine.
Repair or replace damaged wiring, and fix any open circuit or short to voltage found in the sensor harness.
Clean or replace corroded connector terminals and ensure the connector locks properly.
Restore a poor ground connection at the sensor circuit or the shared ground point.
Replace or repair the control unit only after all other causes are ruled out, and have it programmed as the manufacturer requires.

Can I keep driving?

Low severity

The car can normally be driven while you book it in, as this is usually a sensor or wiring fault. If the oil pressure warning light comes on, or the engine feels or sounds wrong, stop and check the oil level before driving further.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.