Skip to content
Book on WhatsApp

P2039

Reductant Injection Air Pressure Sensor A Circuit Low

The reductant injection air-pressure sensor A reads below its lower plausibility limit — short to ground or sensor internal short.

  • Check engine light: Yes
  • Emissions related: Yes
  • Repair difficulty: medium

Symptoms

  • Check engine light or NOx warning on
  • AdBlue/DEF level or quality warning
  • Possible no-start countdown after ignore period
  • Failed emissions inspection (NOx)

Common causes

Ordered by how often each turns out to be the cause.

  • Short to groundCommon
  • Connector pins corroded - high contact resistanceLess likely
  • Harness chafing through insulationLess likely

Parts involved

  • Reductant Air Pressure Sensor

P2039 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.