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SPN 1761 FMI 4

Aftertreatment 1 DEF Tank Volume — Voltage below normal or shorted low.
The sensor circuit voltage is lower than it should ever be, usually near zero.

What the SPN covers: How full the diesel exhaust fluid (DEF) tank is. More on SPN 1761.

What FMI 4 usually points to: Signal wire shorted to ground, a lost 5 V reference, or an open signal wire on a pulled-down circuit. More on FMI 4.

Severity

MEDIUM — fix soon

Running low on DEF leads to inducement derates and eventually a speed limit. Fill up.

Likely causes

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. Low DEF level
  3. Frozen DEF
  4. Faulty level sensor (often combined with temperature/quality sensor)
  5. Wiring fault

Checks & fixes (easiest first)

  1. Inspect the connector and harness for this circuit: corrosion, water, chafing, backed-out pins
  2. Check the reference voltage, ground and signal at the component per OEM pin-out
  3. Fill the tank with fresh, certified DEF
  4. Check the tank sender for crystal buildup
  5. Compare gauge with a visual check

FAQ

What does SPN 1761 FMI 4 mean?

Aftertreatment 1 DEF Tank Volume — voltage below normal or shorted low. The sensor circuit voltage is lower than it should ever be, usually near zero.

Is SPN 1761 FMI 4 serious?

Running low on DEF leads to inducement derates and eventually a speed limit. Fill up.

What should I check first for SPN 1761 FMI 4?

Inspect the connector and harness for this circuit: corrosion, water, chafing, backed-out pins; Check the reference voltage, ground and signal at the component per OEM pin-out; Fill the tank with fresh, certified DEF.