P0407

P0407 means the EGR position sensor B signal is reading low — same fault mode as P0405 but on the second of two position sensors used on EGR valves with redundant or dual-feedback designs. Dual-sensor EGRs are common on modern emissions-strict platforms (post-2010 Ford, Mazda, some VW/Audi TDI) where the ECM cross-checks two independent position signals to satisfy OBD-II rationality requirements; if either signal disagrees with the other or drops out of range, the ECM throws the corresponding A or B code. Diagnostic ladder is identical to P0405: backprobe the B-signal pin with the connector seated and read at-rest voltage (spec typically 0.6-0.9V closed); unplug and verify 5V reference and ground; check signal-wire continuity from connector to ECM for chafe or open. The added wrinkle on dual-sensor valves is that you can have one sensor failed and one healthy — the ECM will still throw P0407 even though the valve still reports position accurately on sensor A. On diesel applications (Cummins 6.7L, Powerstroke 6.7L, Sprinter OM642), soot contamination inside the EGR valve assembly can short the B-signal trace on the sensor PCB to chassis ground through wet soot — cleaning rarely fixes it, the assembly replaces.

Vehicle-specific patterns: 2011-2016 Ford 6.7L Powerstroke throws P0407 from soot contamination of the dual-position-sensor EGR valve — the valve assembly is $400-$700 and is the only repair; cleaning attempts fail because the soot conducts. 2007-2014 Cummins 6.7L (Ram 2500/3500) throws P0407 from the same dual-sensor soot pattern — valve replaces with a Cummins-branded service kit. 2010-2014 VW/Audi 2.0L TDI (CBEA, CJAA engines) throws P0407 from internal EGR cooler failure routing soot into the position sensor cavity; the cooler and valve replace together. 2012-2016 Mercedes Sprinter OM642 3.0L V6 diesel throws P0407 from a known EGR actuator failure with a Mercedes TSB and extended coverage — verify VIN before quoting out of pocket. Estimated repair: $200 (light-duty valve) to $1,400+ (diesel EGR valve + cooler).