P0491: 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 P0491 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

6 complaints filed with NHTSA mention P0491, 5 of them since 2015, across 6 different models. The component owners most often filed it under: electrical system.

Manufacturer service bulletins that name P0491

5 technical service bulletins and manufacturer communications filed with NHTSA mention P0491, from 3 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:

  • AUDI A4 (2009, 2010, 2011), bulletin 10210604: DTC P0491 and P0492 (Secondary Air System Insufficient Flow, Bank 1/2) are stored at the same time.
  • ASTON MARTIN DB11 (2017, 2018, 2019), bulletin 10154220: V12 Secondary air injection codes P0492 P0491
  • AUDI Q7 (2011, 2012, 2013, 2014), bulletin 10119937: The MIL is on due to DTCs P0491 and P0492 being stored in the ECM.
  • VOLKSWAGEN BEETLE (2013, 2014, 2015), bulletin 10122989: Technical Bulletin (Update Programming, DTCs P0491 and or P2440 stored in the ECM Fault Memory): Current ECM software are causing erroneous faults. This document contains the codes necessary to update the software to dia…

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.