P1402

P1402 on a Mercedes with the M642 3.0L OM642 BlueTec diesel (E320 BlueTec, E350 BlueTec, ML320/ML350 BlueTec, GL320, Sprinter) is an EGR Valve Position Sensor fault — the EGR valve is an electrically-actuated butterfly with an integrated position-feedback sensor, and the ECU compares commanded position (0-100% open) against the sensor's actual reading. The position sensor outputs a 0-4.5V signal that scales to 0-100% open; healthy operation shows ~0.5V at fully closed and ~4.2V at fully open, with the ECU expecting the sensor reading to track commanded position within ±5% during operation. P1402 sets when the sensor signal stays stuck, reads outside the 0.3-4.7V plausible range, or fails to respond to commanded movement within ~500ms. Diagnostic order: (1) Scan live data — watch "EGR Position Commanded" versus "EGR Position Actual" through an idle-to-2000-RPM sweep; if commanded climbs to 60% and actual stays at 5%, the valve is mechanically seized with soot (extremely common on OM642 at 80-120K mi). (2) Pull the EGR valve, inspect for the carbon brick that always accumulates on the butterfly shaft — most OM642 EGR valves can be cleaned with carb cleaner and a brass brush, then reinstalled with a new gasket for $25. (3) If cleaned valve still throws the code, the integrated position sensor is bad and the valve must be replaced as a unit (Mercedes doesn't sell the sensor separately on this generation). Expensive-misdiagnosis caveat: don't replace the EGR valve before checking the EGR cooler and intake manifold for catastrophic soot loading — on the OM642, a clogged EGR cooler creates backpressure that physically prevents the valve from reaching commanded position, and a brand-new $700 EGR valve will throw P1402 again within 200 miles if the cooler and intake aren't walnut-blasted or replaced at the same time. The full "EGR delete and intake clean" job on an OM642 runs 6-8 shop hours.

Vehicle-specific patterns: 2007-2009 Mercedes E320 BlueTec (W211) and 2010-2012 E350 BlueTec (W212) with the OM642 are the canonical P1402 vehicles — soot accumulation in the EGR cooler and intake manifold is so consistent at the 100K-mile mark that the repair has its own labor-time entry at every diesel-spec independent shop. 2007-2012 Mercedes ML320 BlueTec / ML350 BlueTec / GL320 BlueTec / R320 BlueTec with the same OM642 throws identical patterns, with added soot loading in cold-climate markets where short-trip driving prevents regen cycles. 2007-2018 Sprinter vans with the OM642 (2500/3500 series) see P1402 even more aggressively because delivery-route stop-and-go usage prevents DPF regens — fleet operators replace EGR valves on a 60-80K mile preventive schedule. The closely-related M272/M273 gasoline V6/V8 platforms (W203/W204/W211/W212/W221, 2005-2014) don't use this code the same way — their EGR strategy is internal via cam timing, and their famous failure mode is balance-shaft gear wear setting P0016/P0017. Estimated repair: $150 (clean and reinstall existing valve) to $2,800 (new EGR valve, new EGR cooler, intake manifold walnut blast, all gaskets).