International · DEF Quality SensorHigh

International SPN 3364 FMI 9: DEF Quality Sensor Communication Fault

SPN 3364 FMI 9 (FMI 9) — Aftertreatment 1 DEF Tank - Liquid Quality Parameter - Abnormal Update Rate

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Quick Answer

SPN 3364 FMI 9 means the ECM lost a steady communication update rate with the DEF quality sensor, most often from a loose connector at the tank sending unit.

Overview: International SPN 3364 FMI 9

This code is nearly always a connector or wiring issue rather than a failed sensor. Check the tank connector's locking tab before ordering parts.

Repair Snapshot

Time

1 - 2 Hours

Difficulty

Intermediate

Parts Cost

$150 - $350

Dealer Labor

$400+

Tools Required

  • Multimeter
  • Electrical Contact Cleaner
  • Wiring Diagram

What SPN 3364 FMI 9 Means

SPN 3364 FMI 9 on International trucks means the ECM has lost a consistent communication update rate with the DEF quality sensor. Left unresolved, this leads to an SCR inducement derate.

Symptoms Drivers Notice

  • Amber check-engine lamp with a DEF system warning message
  • Progressive derate stages if unaddressed
  • DEF gauge behaving erratically
  • No immediate power loss at the earliest stage

Most Likely Root Causes

Loose or corroded DEF tank sender connector

Common

A broken locking tab lets vibration work the connector loose over time.

Chafed harness near the tank or frame rail

Occasional

Repeated flex and vibration wears insulation thin at contact points.

Water intrusion at the connector

Occasional

Frequent pressure washing can force moisture past a degraded seal.

Common Misdiagnoses (Don't Waste Parts)

Replacing the sensor as the first step

Why it happens: It's the named component.

Do this instead: Inspect and clean the connector first.

Blaming DEF quality itself

Why it happens: The fault mentions liquid quality parameter.

Do this instead: FMI 9 is a communication timing fault - focus on the connection first.

Master Tech Commentary

Mechanic's Notes

Real-world tip: check the connector locking tab first - a broken tab lets vibration back the connector out just enough to disrupt communication.

Step-by-Step Diagnostic Procedure

  1. Step 1: Inspect the DEF tank sending unit connector for corrosion or a loose pin.
  2. Step 2: Check the harness between the tank and ECM for chafing near the frame rail.
  3. Step 3: Verify DEF quality with fresh, sealed, certified fluid.
  4. Step 4: Check for water intrusion at the sensor connector.
  5. Step 5: Confirm sensor firmware matches the current ECM software level after any recent update.

Live Data & Freeze-Frame Tips

Watch the DEF quality sensor's update rate while wiggling the connector - dropouts confirm a connection issue.

Safety Warnings

  • DEF can be corrosive to some metals if it leaks - clean any residue promptly.
  • Wear gloves when handling DEF system components.

When to Limp In vs Tow

Not required at this stage - address before it progresses to a full inducement derate.

Prevention Tips for Fleets & Owner-Operators

  • Secure the connector's locking tab fully during service.
  • Inspect the DEF tank connector at PM intervals.
  • Use only certified DEF from sealed containers.

Related Fault Codes

SPN 5246

The SCR operator inducement code that follows if this fault isn't resolved.

Frequently Asked Questions

Will this cause a derate right away?

Not immediately, but continued operation without a fix will progress through inducement stages.

Is the sensor usually bad?

Less often than the connector - always check the connection first.

Can bad DEF cause this specific code?

Possible but less common than a connector issue.

How do I confirm a connector problem?

Wiggle the connector while watching live sensor update-rate data for dropouts.

Is this an expensive repair?

Usually inexpensive if it's a connector fix.