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DTC codes / P01xx · Fuel and air metering / P0198

P0198Engine Oil Temperature Sensor High

P0198 means the powertrain control module (PCM) has detected an abnormally high voltage signal from the engine oil temperature (EOT) sensor circuit, which it interprets as an excessively hot oil condition or an open circuit. The sensor is a thermistor whose resistance drops as oil temperature rises, so a high signal voltage typically indicates a wiring fault, a disconnected sensor, or a failed sensor rather than genuine overheating.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Oil temperature gauge or warning message showing an implausibly high reading or pegged at maximum
  • Reduced engine performance or power derating if the PCM enters a protection strategy based on the false hot-oil signal
  • Poor fuel economy or altered shift quality as the PCM adjusts fueling and transmission behavior for a perceived hot condition
  • In rare cases, a no-start or rough-running condition if the false signal severely corrupts the PCM's temperature-based calculations

Common causes, most likely first

  1. Open circuit in the EOT sensor signal or ground wiring, including a broken wire, corroded terminal, or disconnected connector
  2. Failed EOT sensor with an open internal thermistor element
  3. High-resistance connection at the sensor pigtail or PCM connector due to corrosion or pin tension loss
  4. Short to voltage on the signal wire from chafing against a hotter or moving component
  5. PCM internal fault misreading the sensor input, though this is uncommon
  6. Aftermarket or incorrect sensor installed that does not match the PCM's calibration

How to diagnose and fix it

  1. Connect a scan tool and record the EOT sensor voltage and temperature readings with the key on and engine off, then compare them to ambient temperature to confirm the signal is implausible.
  2. Visually inspect the EOT sensor connector and wiring harness for corrosion, loose pins, chafing, or a disconnected plug, repairing any obvious damage.
  3. Measure resistance across the EOT sensor terminals with a multimeter and compare the value to the manufacturer's temperature-resistance chart for the current ambient temperature.
  4. Backprobe the signal wire at the PCM connector and check for an open circuit or short to voltage while wiggling the harness to expose intermittent faults.
  5. Check the sensor ground circuit for excessive resistance by measuring voltage drop between the sensor ground pin and battery negative.
  6. Replace the EOT sensor if resistance testing confirms an open or out-of-spec thermistor, then clear the code and verify the live data reads correctly.
  7. If the sensor and wiring test good, perform a continuity and voltage-drop test on the entire circuit to the PCM before condemning the PCM itself.

Why a hot oil reading is usually a wiring fault

  • A high-voltage EOT signal almost always means the circuit is open or the sensor has failed, not that the engine oil is actually overheating, so do not start replacing oil pumps or coolers based on this code alone.
  • Many vehicles share the EOT sensor signal with other temperature sensors or route it through a common splice pack, so a fault in a related circuit can set P0198 even when the EOT sensor itself is fine.
  • Intermittent P0198 codes that appear only on cold mornings or after hitting a bump often point to a hairline crack in the sensor element or a loose connector pin rather than a hard failure.
  • Some PCMs default to a fixed oil temperature value when the EOT signal is lost, which can mask driveability symptoms and make the code the only clue to a real circuit problem.
  • Checking live EOT data against a known-good infrared thermometer reading at the oil pan is a quick way to separate a sensor calibration error from a wiring fault.

Can I keep driving with P0198?

You can usually drive the vehicle short distances to a repair shop because the code most often reflects a sensor circuit fault rather than actual oil overheating, but avoid heavy loads, towing, or sustained high-speed driving until the fault is repaired. If the oil temperature gauge is pegged high or the engine enters limp mode, stop driving and have the vehicle towed to prevent potential engine damage from a genuine overheating condition.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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