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P238A

Water in Fuel Sensor B Circuit

A general circuit fault on the secondary water-in-fuel sensor B - typically used on diesel systems with two filter housings (pre-pump and post-pump). The ECU loses water-detection feedback on this stage; risk of water reaching the high-pressure pump and injectors.

  • Check engine light: Yes
  • Emissions related: No
  • Repair difficulty: easy

Common causes

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

  • Open in sensor or wiringCommon

Parts involved

  • Water In Fuel Sensor B
  • Fuel Filter Housing B

P238A 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.