If you own a Detroit Diesel (DD13, DD15, or DD16), you know how critical the SCR system is for keeping your truck compliant and on the road. When fault codes appear, running an SCR Efficiency Test can help confirm whether your aftertreatment system is performing properly.
With OTR Diagnostics, you can run this test from your phone, but Detroit Diesel engines have one unique requirement before the test will begin.
For a deeper dive into advanced fault codes, check out our OTR Diagnostics Closer Look - Advanced Fault Codes Explained and learn What is OTR Diagnostics?.
Why the SCR Efficiency Test Matters
The SCR (Selective Catalytic Reduction) system reduces NOx emissions. If it isn’t working properly, you may experience derates, fault codes, and downtime. Running an SCR Efficiency Test allows you to:
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Confirm whether your SCR system is functioning correctly.
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Narrow down if the issue is a sensor, dosing system, or the SCR itself.
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Avoid unnecessary trips to the dealer by testing directly on the road.
For context on aftertreatment components, see What is an aftertreatment system? (...and why should I care?) and Mastering your truck’s aftertreatment system: 9 must-know components.
Step-by-Step: Running the SCR Efficiency Test on Detroit
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Open the OTR Diagnostics app and select SCR Efficiency Test.
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The app sends the request to your ECM.
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On Detroit Diesel engines, the test won’t start automatically.
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To confirm, press and hold your “Regen/DPF” button:
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Older DD models: This is a physical button on the dash, most likely your forced regen button. Learn more about how to initiate forced DPF regen with OTR Diagnostics: A detailed guide.
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Newer DD models: This is a button on your digital dash display.
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Hold until the test begins, then OTR Diagnostics completes the SCR test for you.
NOTE: Without pressing that button, the test will not run.
Pro Tips for Detroit Diesel Owners
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Locate your confirmation button. It may be physical or digital, depending on the model year.
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Stay parked and safe. The test requires your truck to be stationary.
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Watch for confirmation. The OTR Diagnostics app will display progress once the test is running.
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Be patient. The SCR Efficiency Test can take time; don’t interrupt it.
For other diagnostics tips and tricks, check out How to Get the Most Out of Your OTR Diagnostics Tool: Advanced Tips and 3 Recommended Steps to Diagnosing a Fault Code (3-Minute Read).
Why Detroit Diesel Engines Require This Extra Step
Detroit Diesel designed this confirmation step as a driver acknowledgment. By pressing the Regen/DPF button (physical or digital), you’re confirming that the test should begin. This prevents accidental triggers and ensures you’re ready for the process.
For related troubleshooting, check out What Does ‘SCR NOx Conversion Efficiency Low’ Mean On Detroit Diesel DD13, DD15, DD16?.
Following this step ensures your SCR Efficiency Test runs smoothly and keeps your Detroit Diesel truck performing at its best. Have a question about this process or your model year? Contact us today, and we’ll walk you through it.
Understanding fault codes: what they mean and how to use them