Truck Stuck at 5 MPH Derate? Here’s the REAL Fix (2025 Guide)

Truck Stuck at 5 MPH Derate? Here’s the REAL Fix (2025 Guide)

Is your truck crawling at 5 MPH, no matter how hard you press the throttle?

You’re dealing with the dreaded 5 MPH DEF Derate — the most severe emissions lockout a diesel truck can trigger.

This guide explains:

  • Why 5 MPH derate happens

  • What codes cause it

  • What parts people replace unnecessarily

  • The only way to get out of 5 MPH derate

  • Step-by-step instructions to fix it

  • The tools you MUST have to clear it

This is exactly how dealerships clear 5 MPH derate…
👉 And you can do it at home.

🚨 What Is 5 MPH Derate?

5 MPH derate is a mandatory emissions lockout triggered when the truck determines the DEF/SCR system can no longer reduce NOx emissions.

To protect the atmosphere and enforce EPA regulations, the ECM limits you to:

👉 5 miles per hour max

You cannot clear it by:

  • Disconnecting batteries ❌

  • Clearing codes ❌

  • Resetting maintenance lights ❌

  • Driving on the highway ❌

  • Cycling the key ❌

  • Adding fresh DEF ❌

Once 5 MPH derate is active, only one thing can remove it:
OEM-level resets using professional diagnostic software.

⚠️ What Triggers 5 MPH Derate?

The most common triggers are:

1. SPN 5246 – DEF System Failure (Most Common)

This code appears on almost EVERY 5 MPH derate case.

2. SCR Efficiency Codes

  • P20EE

  • SPN 4364

  • SPN 4374

These indicate the SCR is not reducing NOx properly.

3. NOx Sensor Failure

If one sensor dies or gives false readings:

  • The ECM thinks DEF isn’t working

  • → 5 MPH derate begins

4. DEF Pump or Doser Failure

If the truck cannot dose DEF properly, derate is forced.

5. Bad DEF Quality

Contaminated, old, or watered DEF instantly triggers derate.

6. DPF Full / Soot Load High

If the truck can’t complete regen cycles, it eventually derates.

7. Sensor Resets NOT Performed After Repairs

This is a huge overlooked reason.

Example:
You install a new NOx sensor → truck STILL derates because you didn’t reset SCR adaptations.

❌ What NOT to Do

Truck owners waste thousands because they don’t know this:

❌ 5 MPH derate CANNOT be cleared with a code reader.

OBD2 scanners do nothing.

❌ Replacing random parts will NOT clear derate.

You can install a brand-new DEF pump and still be stuck.

❌ You cannot “drive it off.”

Once active, derate is 100% software-controlled.

❌ Do NOT unplug sensors.

It makes the derate harder to remove.

🛠️ The ONLY Way to Clear 5 MPH Derate

You MUST perform all of the following using dealer-level diagnostic software:

  1. DEF Doser Test

  2. DEF Pump Pressure Test

  3. NOx Sensor Reset

  4. SCR Efficiency Reset

  5. DEF System Reset

  6. Aftertreatment Learned Data Reset

  7. Forced Regen (Mandatory)

  8. Clear All Aftertreatment Faults

If ANY of these steps are skipped, 5 MPH derate will return immediately.

This is why dealership visits cost $600–$1500+ for emissions repairs.

⭐ STEP-BY-STEP: How to Clear 5 MPH Derate at Home

STEP 1 — Connect your diesel diagnostic laptop

Using:

  • JPRO

  • Diesel Tech

  • Cummins Insite

  • Detroit DDDL

  • Paccar Davie

  • Volvo Tech Tool

STEP 2 — Read SCR/DEF/NOx Codes

You must identify the root cause.

STEP 3 — Run DEF Dosing Test

Confirms pump pressure & injector spraying.

STEP 4 — Replace faulty parts IF needed

Most common failures:

  • NOx sensors

  • DEF pump

  • Doser injector

  • SCR catalyst (rare)

  • Temperature sensors

STEP 5 — Perform ALL Aftertreatment Resets

This is the key step.

STEP 6 — Run a Forced Regen

Required to finalize all resets.

STEP 7 — Clear All Codes

Truck exits derate immediately once tests pass.

💻 Tools Required to Clear 5 MPH Derate

You MUST have:

✔ Dealer-level Diesel Software

(JPRO, Diesel Tech, Insite, DDDL, Davie, VTT)

✔ Nexiq USB-Link 3

Required for RP1210 heavy-duty communication.

✔ Laptop configured for diesel diagnostics

(preloaded is best — saves hours)

✔ Stable power source

Regen takes 20–45 min.

DieselScanners kits include:

  • Fully loaded software

  • Nexiq USB-Link 3

  • SCR/NOx/DEF resets

  • Forced regen capability

  • Lifetime support

  • Step-by-step videos

📞 Need immediate help? Call Us: (800) 987-4850

💲 Why Clearing Derate Yourself Saves Serious Money

Dealership costs:

Service Cost
Diagnose Aftertreatment $300–$450
SCR Reset $200–$350
NOx Resets $150–$250
Forced Regen $150–$300
DEF Pump Replacement $900–$1500
Total $1,200–$3,000

Your own kit:

👉 Clears derate instantly at home
👉 Runs unlimited regens
👉 Resets sensors and dosing system
👉 Pays for itself in 1–2 uses

🚛 Get Out of 5 MPH Derate Today

5 MPH derate is designed to make your truck undrivable — unless you have the right diagnostic tools.

DieselScanners diagnostic kits give you:

  • SCR resets

  • NOx resets

  • DEF tests

  • Forced regen

  • Complete derate clearing capability

📞 Need help right now? Call us: (800) 987-4850
👉 Shop DieselScanners diagnostic laptop kits

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