How to Fix SPN 3246 FMI 0/16 – DPF Outlet Temperature Sensor Fault

How to Fix SPN 3246 FMI 0/16 – DPF Outlet Temperature Sensor Fault

If your truck is showing SPN 3246 with FMI 0 or FMI 16, it means your DPF outlet temperature sensor is reading incorrectly, out of range, or completely failed.

This sensor is CRITICAL because:

  • It measures exhaust temperature exiting the DPF

  • It determines whether a regen is safe and successful

  • It controls DEF dosing and SCR activation

When SPN 3246 FMI 0/16 appears, your truck will:

  • Fail to regen properly

  • Enter a soot-loading cycle

  • Eventually derate to protect the aftertreatment system

This code is extremely common on:

  • Cummins

  • Detroit

  • Paccar

  • Volvo/Mack

  • International A26

🚨 What SPN 3246 Means by FMI

FMI 0 — Data valid but above normal range

Sensor reading TOO HIGH (unrealistic)
→ Sensor shorted, overheated, or circuit failure.

FMI 16 — Data valid but below normal range

Sensor reading TOO LOW
→ Open circuit, broken wire, or dead sensor.

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⚠️ Symptoms of SPN 3246

Your truck may experience:

  • Frequent or failed regens

  • Check engine & aftertreatment lamps

  • Exhaust temps stuck at impossible values (like -40°F or 1,600°F)

  • High soot load

  • 5 MPH derate if ignored

This sensor MUST be functioning for regens to occur.

⚠️ Most Common Causes of SPN 3246 FMI 0/16

🔹 1. Failed DPF Outlet Temp Sensor (MOST COMMON)

These sensors fail from age, heat cycling, or soot contamination.

🔹 2. Damaged Wiring Harness

Often melted near the DPF or SCR.

🔹 3. Connector Corrosion

Moisture = high resistance = incorrect readings.

🔹 4. Open Circuit (FMI 16)

Broken wire → sensor reads cold → regen inhibited.

🔹 5. Short to Voltage (FMI 0)

Damaged harness → sensor reads extremely hot → system shuts down.

🔹 6. DPF Extremely Plugged

Backpressure causes overheating → sensor readings spike.

🔧 How to Diagnose SPN 3246 Using a Truck Scanner

You MUST use a dealer-level scanner because you need to read:

  • Actual temp vs expected temp

  • Temp during regen

  • Temp deltas from DOC → DPF → SCR

  • Aftertreatment status

Here’s how to diagnose it properly:

1️⃣ Read the DPF Outlet Temperature Value

With the engine cold:

  • Sensor should read close to ambient

  • If sensor shows -40°F or 900°F → sensor FAILED

2️⃣ Check Temperature Increase During Regen

During a regen:

  • DPF outlet temp should reach 900–1,200°F

  • If the value does not rise → failed sensor.

  • If value spikes instantly → short or melted wiring.

3️⃣ Compare DOC → DPF → SCR Temperature Progression

Proper pattern:

DOC Inlet → DOC Outlet → DPF Inlet → DPF Outlet → SCR Temp

If one sensor is out of line → that’s your failed circuit.

4️⃣ Inspect Wiring Harness

Check near:

  • DPF body

  • Heat shields

  • Stainless steel flex pipe

  • SCR inlet

Look for:

✔ Melted insulation
✔ Broken wires
✔ Cracked connectors
✔ Green corrosion on pins

5️⃣ Perform a Sensor Override Test (If Available)

Some truck scanners allow:

✔ Temp substitute value test
✔ Temp rationality test
✔ Sensor circuit test

If values stabilize with substitute → sensor is bad.

🛠 How to Fix SPN 3246 (By Root Cause)

✔ If Sensor is Dead or Erratic

➡ Replace DPF outlet temp sensor
➡ Clear fault
➡ Run regen to confirm fix

✔ If Wiring is Melted or corroded

➡ Repair wiring harness
➡ Replace connectors
➡ Use heat-resistant loom
➡ Clear code and retest

✔ If DPF is Plugged

Symptoms:

  • High backpressure

  • Very high temp readings

  • Regen fails constantly

Fix:

➡ Perform forced regen
➡ If regen fails → clean or replace DPF

✔ If FMI 0 is Present

Likely short to voltage → replace sensor or harness.

✔ If FMI 16 is Present

Likely open circuit → repair wire or connector.

🚫 MYTHS About SPN 3246 FMI 0/16

❌ “Clearing the code will fix it.”

The ECM rechecks temps every second.

❌ “A parked regen will burn the soot away.”

Not when the sensor is giving impossible readings.

❌ “It’s just a sensor — ignore it.”

Ignoring leads to soot overload and DPF replacement ($2,500–$7,000).

❌ “You can bypass the sensor.”

Doing so triggers an instant derate.

⭐ The Only Professional Way to Fix SPN 3246

Your scanner MUST allow you to:

✔ View live temp data
✔ Command regenerations
✔ Run sensor rationality tests
✔ Reset aftertreatment system
✔ Verify DPF temperature rise

The DieselScanners™ Laptop Kit provides every one of these capabilities.

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The #1 tool for diagnosing DPF temperature sensor and aftertreatment issues.

Why truckers choose DieselScanners:

✔ Full aftertreatment live data
✔ DPF temp sensor diagnostics
✔ Forced regen capability
✔ Temp rationality tests
✔ Works on all major engines
✔ Comes pre-installed and activated
✔ No subscription fees, ever

👉 Fix SPN 3246 today at DieselScanners.com

📌 Final Takeaway

SPN 3246 FMI 0/16 means your DPF outlet temp sensor is giving incorrect readings due to:

  • Sensor failure

  • Broken wiring

  • Circuit short

  • DPF overheating

This sensor is REQUIRED for regeneration and DEF dosing.
With a proper truck scanner, you can:

  • Diagnose the sensor

  • Inspect wiring

  • Command a regen

  • Verify temperature rise

  • Clear derates

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