P1400

P1400 is the DPFE (Differential Pressure Feedback EGR) sensor circuit low code — the DPFE is a small black plastic box mounted on or near the EGR valve that measures the pressure differential across a metering orifice in the EGR tube. P1400 means the sensor signal voltage stayed below the lower limit (typically below 0.2V when it should idle at 0.9V to 1.1V key-on engine-off with no EGR flow). It is one of the most-searched Ford codes from the late 1990s through the mid-2000s. Cheapest-first ladder: with key-on engine-off, back-probe the DPFE signal wire and check voltage — spec is 0.9V to 1.1V at rest. A reading below 0.2V points to either a failed sensor, an open signal wire to PCM, or a missing 5V reference. Check the 5V reference at the DPFE connector — spec is 4.9V to 5.1V; if absent, the wire is open back to the PCM. Inspect the two rubber hoses from DPFE to the steel EGR tube — they crack and fall off. Replace the DPFE with the Motorcraft updated black-plastic-housing part DPFE15 (the original aluminum housing DPFE7 fails predictably from heat). The expensive misdiagnosis is replacing the EGR valve ($120 to $260) when the sensor on top of it is the actual fault.

Vehicle-specific patterns: 1996-2004 Ford Mustang GT 4.6L 2V cars run the original aluminum DPFE that fails between 80,000 and 130,000 miles — the updated plastic Motorcraft DPFE15 is a direct bolt-in. 1999-2004 Ford F-150 4.6L/5.4L 2V trucks suffer identical DPFE failure plus cracked steel EGR tubes from heat cycling. 2001-2007 Ford Taurus 3.0L Vulcan/Duratec V6 sees P1400 with chronic regularity — the DPFE mounts on the firewall bracket and bakes from exhaust radiant heat. 1997-2002 Ford Expedition 5.4L sets P1400 plus rough idle when the DPFE fails and the EGR sticks partly open from carbon. Estimated repair: $40 to $280.