SPN 3597 — DEF/urea fluid quality — out of specification

Likely causes

• Contaminated DEF (water, diesel fuel, or cleaning chemicals)
• Expired or poorly stored DEF (winter freeze without protection)
• Faulty DEF quality sensor or dosing unit

Recommended checks

1. 1

   Drain and rinse the DEF tank; refill with ISO 22241-certified DEF

2. 2

   Store DEF between about 12 °F and 86 °F; use a tank heater in winter

3. 3

   Test the quality sensor and DEF dosing unit

Parts to replace

• Certified DEF fluid

  AmazonRockAuto

• DEF filter

  AmazonRockAuto

• DEF quality sensor

  AmazonRockAuto