Urea Dosing System Test (UDST) – CNH SCR Diagnostics & Repair Guide

This comprehensive guide covers the entire UDST procedure — from setup conditions to fault interpretation. It details how to evaluate SCR system integrity, detect blockages, assess pump and injector behavior, and diagnose issues such as air ingress, leaks, and failed evacuations. The manual also includes hydraulic schematics, DCU control logic, pressure thresholds, and diagnostic routines like System Emptying and Flushing. A complete list of failure scenarios, pressure thresholds, and corrective actions is provided with supporting graphs and visuals.

Coverage

• Fundamentals

  • Urea Dosing System Test overview

  • Test purpose and limitations

  • Static test prerequisites

  • Diagnostic routines in EST

• Test Setup & Location

  • Accessing UDST in CNH EST

  • Engine conditions before testing

  • Using EASY ENGINE vs Base EST

• UDST Procedure

  • Step-by-step EST operation

  • Test sequence and expected duration

  • PASS/FAIL interpretation

  • Troubleshooting navigation

• Evaluation and Parameters

  • Pump speed test (1800–3600 rpm)

  • System pressure range (4900–6200 mbar)

  • Throttle test evaluation (1500–4300 mbar differential)

  • Injection verification (≤100 mbar differential)

  • Emptying pressure range (−300 to −50 mbar)

• SCR System Review

  • DEF flow diagram

  • Main components overview (tank, injector, supply module, sensors)

  • NOx reduction process

  • Cooling and heater control systems

• Supply Module Details

  • Bosch Denoxtronic SM layout

  • Pressure control and reverting valve operation

  • Sensor mapping and filtering system

• Dosing Module (Injector)

  • Pressure regulation

  • Check valve design

  • Evacuation and return flow path

• Hydraulic Schematics

  • DEF pressure circuit (5 bar nominal)

  • Cooling and circulation loop

  • Emptying and reverting operation sequence

• DNOx Function Stages

  • Pressure build-up phase

  • Reverting valve check

  • Normal dosing operation

  • Afterrun evacuation logic

• Maintenance & Repair Routines

  • Flushing routine

  • System emptying validation

  • Data saving and report exporting

  • Fault code interpretation (DCU15)

• Failure Scenarios

  • Air in system

  • Low DEF injection

  • High-pressure leaks

  • Reverting valve malfunction

  • Pump or pressure buildup failure

  • Clogged lines and incorrect tubing configuration

Delivery

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