P0197 — Engine oil temperature sensor low input

P0197 identifies low electrical input at the engine-oil temperature sensor, not low physical oil temperature. In an NTC circuit low voltage may be interpreted as an extremely high temperature; the actual condition and the cause require testing. Thresholds and wiring depend on the engine.

Affected system: Engine oil temperature sensing

Symptoms

• Engine warning and implausible live EOT.
• Some vehicles substitute a fallback reading or protection strategy; the code alone does not prove overheating.

Possible causes

• EOT signal short to ground where supported by the diagram.
• Failed NTC element or abnormally low resistance.
• Wet/corroded connector or damaged harness; reference/ECU fault only after ruling these out.

What to check

• Save DTCs, freeze-frame and related reference/temperature faults.
• Compare reported EOT with a cold engine; 'low input' does not mean cold oil.
• Inspect connector pins and wiring with the engine off, particularly chafing points.
• A technician measures the proper sensor signal and return per OEM diagram; 2016 Ford diesel voltage examples are not universal.
• Apply the OEM sensor-versus-harness isolation: persistent low voltage with the sensor disconnected as specified suggests wiring.
• Check disconnected NTC resistance at a known temperature against the OEM chart; never resistance-test energized wiring.
• Repair only the confirmed fault, then verify live EOT and monitor completion.

Also written as: P0197-00, P019700, PO197 (some scan tools add the fault-type byte, e.g. -00).