P0183

P0183 means the ECM is seeing the Fuel Temperature Sensor A signal pinned above its high-input threshold — on a typical 5V-reference circuit the sensor sweeps roughly 4.5V cold (low temp, high resistance NTC thermistor) down to about 0.5V hot (high temp, low resistance), and the code sets when the ECU reads a value stuck near rail voltage (~4.7-5.0V) for longer than the calibration window allows. That's almost always an electrical fault, not a fuel-temperature problem: the sensor is open-circuit or its signal wire is broken/disconnected, not actually reading scorching fuel. Shop-floor diagnostic ladder, cheapest first: (1) unplug the sensor connector and look for green corrosion, fuel saturation, or pushed-back pins — diesel fuel migration through harness sheathing is the #1 cause on trucks past 150k miles, $0 to clean and re-pin. (2) Back-probe the signal wire with a DVOM key-on/engine-off and confirm 5V reference and good ground at the sensor connector; if reference is missing, the harness or ECM driver is at fault, not the sensor. (3) Ohm the sensor cold (should read roughly 2.5-3.5 kOhm at 70F on most Bosch/Denso NTC fuel temp sensors, dropping to ~300-500 ohm at 175F) — an open reading confirms the sensor. (4) Live-data the fuel temp PID with the engine warm: a healthy sensor reports somewhere between 90F and 180F at the supply rail; a stuck-high voltage shows up as -40F or similar minimum-rail value. Expensive-misdiagnosis caveat: don't condemn the high-pressure injection pump or chase a fueling problem on a P0183 alone — the ECU uses fuel-temp to compensate injection quantity, but the code itself almost never originates inside the pump. Replacing a CP3 or CP4 pump because of a P0183 is a $3,000+ mistake.

Vehicle-specific patterns: 2003-2007 Ford 6.0L Powerstroke and 2008-2010 6.4L Powerstroke commonly throw P0183 from the fuel temp sensor mounted in the secondary fuel filter housing on top of the engine — the connector sits under the heat shield and gets cooked by EGR cooler radiant heat; the pins corrode and the sensor reads open. Cheap $35 sensor + harness pigtail repair clears it. 2001-2010 GM Duramax LB7/LLY/LBZ/LMM throws P0183 from the fuel temp sensor integrated into the fuel filter head bracket — water-in-fuel intrusion corrodes the pins long before the sensor element itself fails. 2003-2018 RAM Cummins 5.9L and 6.7L throws P0183 from chafed harness near the CP3 pump where the loom rubs the bracket; check for bare copper before quoting a sensor. 2009-2015 VW TDI 2.0L CR (CBEA/CJAA) throws P0183 from the in-tank fuel temp sender on the lift-pump module — fuel-saturated connector is the usual culprit. 2007-2018 Mercedes Sprinter OM642 3.0L V6 diesel throws P0183 from the fuel temp sensor in the rail-pressure regulator harness, often after a fuel filter change where the tech bumped the connector. Estimated repair: $75 to $400.