P0198 — Engine oil temperature sensor high

P0198 refers to a high electrical input from the engine-oil temperature (EOT) sensor circuit on systems that use this diagnostic. It is not a code proving that the oil itself is too hot. Ford documents P0198/P0195_17 as an EOT circuit-high input; exact limits, connector pins and sensor location are vehicle-dependent. An NTC temperature element can report an implausibly cold value when its circuit is open, but verify the actual circuit design before interpreting the scan reading.

Affected system: Engine-oil temperature sensing

Symptoms

• Engine warning lamp or stored EOT circuit fault; driving may seem normal.
• Oil-temperature live data may be implausible, fixed or inconsistent with a cold-start comparison.
• Engine control can use a substitute oil-temperature value where supported; behavior varies by vehicle.

Possible causes

• Open circuit or poor contact in the EOT signal/return wiring, according to the applicable NTC circuit design.
• Corroded, oil-contaminated or loose connector, or a damaged loom.
• Defective EOT measuring element or combined oil level/temperature sensor, only where the vehicle uses one.
• Incorrect supply/reference or ECU input fault considered only after the circuit and component have been tested.

What to check

• 1. Save P0198 and freeze-frame; check whether P0195, P0196, P0197, cooling or electrical-supply codes also exist. Do not infer oil overheating from the word 'high'.
• 2. Identify the EOT sensor and ECU pinout in the exact engine wiring diagram. It may be a separate component or integrated into an oil-level module; do not assume all engines have the same circuit.
• 3. With the engine fully cold, compare available EOT, coolant and ambient readings. A fixed or implausible EOT value suggests a signal problem but is not enough by itself to condemn a sensor.
• 4. Switch off the engine and inspect the identified connector and nearby harness for oil, water, corrosion, bent pins, chafing and recent repair damage; correct obvious defects.
• 5. With suitable workshop equipment and the manufacturer's procedure, check signal/reference and return wiring for opens, shorts and poor terminal contact. A high ECU input that changes when wiring is repaired implicates the circuit rather than actual oil heat.
• 6. If the circuit is sound, measure the EOT element by the OEM temperature-versus-resistance or voltage specification; a thermistor comparison must use its exact reference table, not a universal resistance threshold.
• 7. Only then consider replacement of the failed sensor or combined module. After repair, confirm plausible temperature change during warm-up and absence of a recurring P0198 under the original monitor conditions.
• 8. If there is independent evidence of genuinely dangerous oil temperature, low oil pressure or a red oil warning, stop the engine safely and diagnose that issue separately; this circuit code does not establish those conditions.

Also written as: P0198-00, P019800, PO198 (some scan tools add the fault-type byte, e.g. -00).