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SPN 3364 FMI 2

Aftertreatment 1 DEF Quality — Data erratic, intermittent, or incorrect.
The signal jumps around, drops in and out, or disagrees with other information the controller has.

What the SPN covers: Whether the fluid in the DEF tank has the right urea concentration. More on SPN 3364.

What FMI 2 usually points to: Loose or corroded connectors, chafed wiring, a failing sensor, or two redundant sensors that do not agree. More on FMI 2.

Severity

MEDIUM — fix soon

Poor DEF quality causes inducement derates. Drain and refill with fresh certified DEF.

Likely causes

  1. Diluted or contaminated DEF (water, coolant, wrong fluid)
  2. Old DEF that has degraded in heat
  3. Faulty quality sensor

Checks & fixes (easiest first)

  1. Test DEF with a refractometer
  2. Drain, flush and refill with fresh DEF
  3. Inspect the tank sender for contamination

FAQ

What does SPN 3364 FMI 2 mean?

Aftertreatment 1 DEF Quality — data erratic, intermittent, or incorrect. The signal jumps around, drops in and out, or disagrees with other information the controller has.

Is SPN 3364 FMI 2 serious?

Poor DEF quality causes inducement derates. Drain and refill with fresh certified DEF.

What should I check first for SPN 3364 FMI 2?

Test DEF with a refractometer; Drain, flush and refill with fresh DEF; Inspect the tank sender for contamination.