Case IH 3515 – Engine Control Unit (ECU), Dosing Control Unit (DCU), or Vehicle Control Module (VCM): SCR Catalyst missing

The Engine Control Unit (ECU) or Dosing Control Unit (DCU) monitors the thermal mass of the Selective Catalytic Reduction (SCR) system by comparing the temperature behavior between the upstream (inlet) and downstream (outlet) exhaust gas temperature sensors. If the temperature relation between the inlet and outlet sensors is not plausible, the system assumes there is no thermal mass between them, indicating the catalyst is physically missing, has been hollowed out, or is severely degraded.

• Farmall
• Maxxum
• Puma
• Magnum
• Optum
• Steiger
• Quadtrac
• Axial-Flow 5130
• Axial-Flow 7230
• Axial-Flow 8230
• Axial-Flow 9240
• N-Series TLBs
• M-Series Crawler Dozers

1. 1

   Check for Primary Sensor Faults: Address any active codes related to the exhaust temperature sensors (e.g., 3517, 3518, 3519) or NOx sensors (e.g., 3521, 3525, 3528) first.

2. 2

   Cold Sensor Plausibility Check: Turn the key to the ON position without starting the engine and check the SCR inlet and outlet temperatures; they should be nearly identical.

3. 3

   Visual Inspection: Physically inspect the SCR canister to ensure it has not been bypassed, replaced with a straight pipe, or tampered with.

4. 4

   Wiring and Harness Check: Inspect the wiring harnesses and connectors for the exhaust gas temperature sensors for damage, corrosion, or short circuits to a high/low source.

1. 1

   Connect Diagnostic Tool

   Connect your CNH Electronic Service Tool (EST) and read all active and inactive fault codes.

2. 2

   Test the Sensors

   If the cold plausibility check reveals a skewed temperature sensor, disconnect the faulty sensor. Inspect the connector pins. If the wiring is intact, replace the faulty Exhaust Gas Temperature (EGT) sensor.

3. 3

   Monitor Live Data

   If the sensors pass the cold check, start the engine and monitor the live SCR inlet and outlet temperatures as the exhaust heats up (this may require putting the machine under load or on a dyno to get exhaust temps over 450°F). The outlet temperature should rise slower than the inlet temperature.

4. 4

   Replace the Catalyst

   If the sensors are reading accurately but the temperature delta remains implausible (proving there is no thermal mass), and you have verified the SCR canister is physically present, the internal catalyst substrate has likely melted, collapsed, or been blown out. You must replace the entire SCR Catalyst Assembly.

5. 5

   Clear Codes and Retest

   After replacing the faulty sensor or catalyst, clear the fault codes using the EST. Perform an aftertreatment system test or a forced regeneration to verify the repair and ensure the catalyst efficiency is restored.