P0199

P0199 is the intermittent version of P0195/P0197/P0198 — the ECU saw the engine oil temperature sensor signal glitch, drop out, or spike momentarily before recovering, and stored the code without committing to a hard high or low designation. Intermittent codes on a sensor that reports correctly when you have it on the scanner are the diagnostic equivalent of chasing a ghost. Cheapest first: wiggle-test the sensor connector and the harness branch between the sensor and the ECM while watching EOT voltage live data — any signal jump during the wiggle nails the fault to that point. Inspect the connector for green corrosion, oil seepage (common when the EOT shares a location with the oil filter housing), and back-out pins. Voltage-drop test the sensor ground from the connector back to battery negative — over 0.1V indicates a degraded ground that intermittently floats the signal. Heat-cycle the engine and watch for the glitch to appear at a specific oil temp; thermal-expansion-related faults are common where the harness routes near exhaust manifolds. Use a graphing scan tool or Pico scope to capture the glitch — a stable trace with sharp dropouts during throttle transients points to a loose connector pin; a noisy trace with constant ripple points to a sensor thermistor going bad internally. The expensive misdiagnosis: replacing the sensor three times because the real fault was a hairline crack in the connector body that only opens up under thermal expansion at 200°F.

Vehicle-specific patterns: 2011-2019 Ford 6.7L Power Stroke sees P0199 from harness chafe and intermittent connector failure on the EOT sensor circuit, often after engine bay washes or fluid leaks compromise the connector seal. 2010-2016 BMW N20 / N55 inline-6 throws P0199 from the well-known oil-filter-housing-gasket leak that intermittently saturates the EOT connector with oil and degrades the signal contact. 2014-2019 GM Duramax L5P / 6.2L direct-injection truck engines sets P0199 from EOT harness rub against the valve-cover bracket or the heat shield on the driver-side exhaust manifold. 2008-2017 VW / Audi 2.0T TSI sees P0199 from the oil-temp sensor integrated into the oil cooler assembly developing intermittent thermistor faults around 100k miles; replacement of the integrated sensor module clears it. Estimated repair: $80 to $550.