P0406: owner reports and bulletins

Powertrain (generic, all makes). We haven't written the explanation for this code yet. Below is what owners and manufacturers have filed with NHTSA.

Got P0406 on your scanner? Tell the mechanic your year, make, model and any symptoms and you'll get the likely cause and what to check first. Ask about this code.

What owners report to NHTSA

9 complaints filed with NHTSA mention P0406, 3 of them since 2015, across 5 different models. The component owners most often filed it under: engine and engine cooling:exhaust system.

Most-reported models

VehicleComplaintsModel years reported
DODGE RAM 150042005, 2007

Manufacturer service bulletins that name P0406

4 technical service bulletins and manufacturer communications filed with NHTSA mention P0406, from 3 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:

  • RAM 2500 (2017), bulletin 10138930: Flash: 6.4L Powertrain Diagnostic and System Enhancements This bulletin involves reprogramming the Powertrain Control Module (PCM) with the latest available software. This bulletin fixes all vehicles listed and also cont…
  • FCA ALL MODELS (2006, 2007, 2008, 2009), bulletin 10150486: Cooled EGR Assembly This Tech Tip applies to Ram DJ, D2, DD trucks for 2014 and 2015 model years equipped with the 6.4 ESA and 6.4 ESB HEMI Heavy Duty engines. Please contact engineering prior to replacing any components…
  • JEEP GRAND CHEROKEE (2011, 2012, 2013), bulletin 10148595: Flash: DTC P0405 / P0406 - MIL Light On This bulletin involves reprogramming the Engine Control Module (ECM) with new software. A small number of customers may report the MIL light is on. On further inspection Diagnostic…

Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.