How to Reset the DEF / SCR System After Repairs (Full 2025 Guide)

How to Reset the DEF / SCR System After Repairs (Full 2025 Guide)

You replaced:

  • A NOx sensor,

  • A DEF pump,

  • A DEF doser/injector,

  • A SCR catalyst,

  • Or cleaned the DEF lines…

…but your truck still has:

  • Check engine light

  • “Service DEF System”

  • “SCR Efficiency Low”

  • SPN 5246

  • SPN 4364

  • P20EE

  • 5 MPH derate

This happens because modern diesel trucks ALWAYS require a DEF/SCR reset after repairs — otherwise the ECM keeps using old learned data and the same code returns.

This guide shows you exactly how to reset your DEF system using professional software (the same way dealerships do).

🚨 Why You MUST Reset the DEF / SCR System After Repairs

When you replace DEF-related components, the ECM still has stored:

  • Old NOx conversion values

  • Old DEF dosing values

  • Old pump pressure values

  • Old SCR efficiency data

  • Old injector cycles

  • Old test results

If you don’t reset the DEF system:

👉 The ECM still thinks the old parts are installed
👉 It fails self-tests
👉 The same code reappears
👉 The truck may stay derated

Resets are REQUIRED on:

  • Cummins

  • Detroit

  • Paccar

  • Volvo/Mack

  • International

  • Duramax

  • Powerstroke

  • RAM 6.7

🔍 When Do You Need a DEF/SCR Reset?

Anytime you replace:

  • NOx sensors (inlet or outlet)

  • DEF pump

  • DEF doser injector

  • DEF quality sensor

  • SCR catalyst

  • DPF

  • Exhaust components before/after SCR

Or when clearing these codes:

  • SPN 5246 (DEF derate)

  • SPN 4364 (NOx sensor)

  • P20EE (SCR efficiency)

  • P207F (DEF quality)

  • P249E (EAS performance)

  • P2BAD / P2BAC

🛠️ How to Reset DEF / SCR System (Step-by-Step)

To properly reset, you must use dealer-level diagnostic software:

  • JPRO

  • Diesel Tech

  • Cummins Insite

  • Detroit DDDL

  • Paccar Davie

  • Volvo Tech Tool

A $50 OBD2 scanner cannot do this.

⭐ STEP 1 — Connect Diagnostic Software

Plug in your:

  • Nexiq USB-Link 3

  • Diesel laptop

  • Start your engine (or key-on, engine-off depending on manufacturer)

Open your diagnostic program.

⭐ STEP 2 — Perform a DEF Dosing Test

This verifies:

  • Pump pressure

  • Doser spray pattern

  • Injector response

  • Pump command health

If this test fails, the reset will not work.

⭐ STEP 3 — Reset the NOx Sensors

Typically labeled as:

  • “NOx Sensor Reset”

  • “NOx Sensor Relearn”

  • “SCR NOx Reset”

You must do this ANY time a NOx sensor is replaced.

⭐ STEP 4 — Run SCR Efficiency Reset

This clears stored catalyst performance values and forces the ECM to relearn new ones.

Appears as:

  • “Aftertreatment SCR Efficiency Reset”

  • “SCR Adaptation Reset”

  • “SCR Value Reset”

⭐ STEP 5 — Perform DEF System Reset

This clears:

  • Old DEF pump pressure data

  • DEF quality history

  • Dosing cycle counts

May be labeled:

  • “DEF Reset”

  • “DEF Doser Reset”

  • “DEF Pump Relearn”

⭐ STEP 6 — Clear All Aftertreatment Codes

Now the ECM will run clean self-tests without old data.

⭐ STEP 7 — Perform a Forced Regen (Mandatory)

A forced regen:

  • Regenerates the DPF

  • Stabilizes exhaust temps

  • Relearns NOx conversion

  • Relearns DEF dosing

  • Confirms SCR operation

This step finishes the reset process.

🎯 Manufacturer-Specific Notes

Cummins

DEF pump replacement absolutely requires:

  • DEF pressure test

  • NOx sensor reset

  • SCR reset

  • Parked regen

Detroit

After dosing block or NOx replacement, you MUST run:

  • “SCR Test 1, 2, 3”

  • “SCR Operator-Induced Regen”

Paccar

Davie won’t let you clear codes until resets are performed.

Volvo/Mack

Aftertreatment “Regeneration Optimization” must run after resets.

💻 Tools Needed to Reset DEF / SCR

  • Diesel laptop with OEM-level software

  • Nexiq USB-Link 3

  • Stable power source

  • Outdoor space for regen

DieselScanners kits come:

✓ Fully configured
✓ Pre-loaded with software
✓ Tested with the Nexiq
✓ Regen ready
✓ NOx/DEF reset capable
✓ Lifetime tech support

📞 Need help choosing a kit? Call Us: (800) 987-4850

💲 Why DIY DEF/SCR Resets Save Thousands

Dealership charges:

Service Cost
NOx Sensor Reset $150–$250
SCR Reset $250–$400
DEF Pump Relearn $150–$300
Forced Regen $150–$300
DEF Doser Test $150–$300

One visit = $700–$1,300
Your own diesel scanner = FREE after purchase

🚛 Take Control of Your DEF System

Don’t let a shop charge you $1,000+ for simple resets.

DieselScanners diagnostic kits let you:

  • Reset NOx sensors

  • Reset SCR system

  • Reset DEF system

  • Run dosing tests

  • Perform forced regens

  • Clear derates

📞 Call us anytime for help: (800) 987-4850
👉 Shop DieselScanners diagnostic kits

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