Engine Oil Temperature Sensor High
What does P0198 mean?
The P0198 code means the vehicle's onboard diagnostic system has detected: Engine Oil Temperature Sensor High. This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Oil temperature reads excessively low (e.g., -40 degrees F)
- Cooling fan may not engage when needed
- Transmission may shift aggressively
- Possible reduced fuel economy
Probable Causes (Ranked by Likelihood)
- Open circuit in the oil temperature sensor (failed sensor) Very High
- Disconnected or loose sensor connector High
- Broken wire in the sensor circuit Moderate
- Corroded connector with poor contact Moderate
- PCM reference voltage or input fault Low
Step-by-Step Diagnostic Procedure
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Read oil temperature on a scan tool. A reading of -40 degrees F with the engine at operating temperature confirms a high circuit (open) condition.
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Check the sensor connector -- it may be simply disconnected or have a pushed-out pin.
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Measure sensor resistance (should be 2,000-3,000 ohms at 68 degrees F). Infinite resistance means the sensor is open.
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Check signal wire continuity from the sensor to the PCM.
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Inspect the wiring for breaks, especially at connectors and routing points.
Frequently Asked Questions
Can I drive with code P0198?
You can drive short distances, but use caution. The cooling fan may not engage when the engine is genuinely hot because the PCM thinks the oil is cold. Monitor your actual temperature gauge and avoid heavy loads.
Why does high circuit mean low temperature?
When the sensor circuit is open, the signal voltage is pulled up toward the 5V reference. With an NTC thermistor, high voltage means low resistance, which corresponds to very cold temperature. The PCM reads -40 degrees F as the default open-circuit value.
Is a disconnected connector the most common cause?
Yes, especially after oil changes or engine service. The sensor connector can be inadvertently knocked loose during maintenance. Always check the connector first before replacing the sensor.