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P201A

Reductant Injection Valve Circuit Range/Performance (Bank 2 Unit 1)

Reductant Injection Valve Circuit Range/Performance (Bank 2 Unit 1): the signal is implausible or outside the valid range. This valve doses reductant (DEF/AdBlue) into the exhaust for SCR NOx reduction.

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

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.

  • DEF crystallisation clogs the dosing nozzleCommon
  • DEF supply pressure below targetPossible
  • Valve coil ageing — slow responsePossible

Parts involved

  • Reductant Injection Valve
  • Reductant Metering Unit
  • SCR Catalyst

P201A 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.