Case IH 19618 – Engine Control Module (ECM): The calculated conversion rate is lower than the limiting value, passive monitoring

During the rapid heat-up phase, the Engine Control Module is monitoring the oxidation catalyst (DOC) and/or Selective Catalytic Reduction (SCR) system, and the calculated exhaust gas conversion rate has fallen below the minimum allowable threshold. This means the aftertreatment system is failing to efficiently convert emissions to acceptable levels.

• Tier 4b
• Case N-Series Tractor Loader Backhoes (580N, 580 Super N, 590 Super N)
• Case IH Puma and Optum series tractors
• Case IH Magnum and Steiger series tractors

1. 1

   Check for active codes related to NOx sensors, exhaust temperature sensors, or DEF dosing and diagnose those first

2. 2

   Inspect the exhaust piping between the turbocharger and the DOC/SCR canister for leaks

3. 3

   Test the DEF fluid using a refractometer to ensure it is at the required 32.5% urea concentration and is not contaminated

4. 4

   Use the CNH Electronic Service Tool (EST) to monitor upstream and downstream NOx sensors and exhaust gas temperature (EGT) sensors for plausibility

5. 5

   Remove and inspect the DEF dosing valve for crystallization, clogging, or a distorted spray pattern

1. 1

   Resolve Underlying Faults

   Fix any exhaust leaks or replace contaminated DEF fluid. Flush the DEF tank and lines if poor-quality fluid is found.

2. 2

   Clean the Dosing Valve

   If the DEF doser is crystallized, clean it using warm distilled water. Do not use harsh chemicals or wire brushes on the nozzle.

3. 3

   Perform a Forced Regeneration / SCR System Test

   Connect the CNH EST laptop and initiate a stationary desoot (forced regeneration) or an SCR efficiency test. Monitor the temperatures across the DOC.

4. 4

   Evaluate Catalyst Performance

   If the exhaust temperatures do not rise sufficiently during the rapid heat-up phase despite proper engine operation, the DOC is likely face-plugged or poisoned. If temperatures are correct but the NOx conversion rate remains below the limiting value, the SCR catalyst has failed.

5. 5

   Replace the Catalyst

   If the system fails the EST efficiency test and all sensors/dosing components are functioning properly, replace the DOC/SCR catalyst canister assembly.

6. 6

   Reset and Validate

   After replacing the necessary components, use the EST to reset the aftertreatment learned values and clear the fault codes. Perform a validation test run under load to ensure code 19618 does not return.