Case IH 19753 – Engine Control Module (ECM): Ratio between DEF/AdBlue Pump Speed and Dosing Valve exceeded.

This code indicates a mismatch in the Selective Catalytic Reduction (SCR) system. The control module has detected that the DEF (Diesel Exhaust Fluid) pump is running at a speed that is disproportionately high compared to the commanded opening of the DEF dosing valve (injector). This typically means the system is struggling to build or maintain the required DEF pressure. The underlying cause is usually a pressure loss due to a leak in the DEF lines, a restricted DEF suction line, a clogged DEF filter, a dosing valve that is stuck open, or a failing DEF pump motor.

• Tier 4b
• Case IH Tier 4B / Stage IV and newer emissions-equipped machines
• Case IH Magnum series (e.g., 235-340 Series 4)
• Case IH Puma and Optum series
• Case IH Steiger series
• Case IH Axial-Flow Combines (e.g., 230 series)

1. 1

   Visual Inspection for Leaks: Inspect all DEF supply lines from the tank to the pump, and from the pump to the dosing valve. Look for white, crystalline buildup which indicates a DEF leak.

2. 2

   Check DEF Level and Quality: Ensure the DEF tank is adequately filled and the fluid is not contaminated or degraded.

3. 3

   Inspect the Dosing Valve: Remove the DEF dosing valve from the exhaust stream and check the nozzle for crystallization/blockage or signs that it is stuck open (leaking fluid when not commanded).

4. 4

   Filter Check: A restricted DEF pump main filter can starve the pump, causing it to overspeed to meet pressure demands.

5. 5

   Pressure Drop Test: Use the CNH Electronic Service Tool (EST) to run a DEF pressure test. Monitor if the pump can build pressure and hold it when the dosing valve is closed.

1. 1

   Purge the System

   Turn the ignition key to the OFF position and wait at least 3 to 5 minutes. The SCR system must complete its purge cycle to suck the DEF back into the tank before you open any lines.

2. 2

   Disconnect Power

   Disconnect the negative battery cable to prevent accidental priming or electrical shorts.

3. 3

   Address Leaks/Blockages

   If a specific DEF line was found to be leaking or pinched during diagnosis, replace the affected line.

4. 4

   Replace the DEF Filter

   Locate the DEF supply module (pump). Unscrew the filter housing cap, remove the old DEF filter element, clean the housing, and install a new filter.

5. 5

   Service the Dosing Valve

   If the dosing valve was heavily crystallized or stuck open, clean the mounting port on the exhaust. Install a new DEF dosing valve and torque the mounting bolts to OEM spec.

6. 6

   Replace the DEF Pump (if necessary)

   If no leaks were found, the filter is new, and the dosing valve is functioning but the pump still overspeeds and fails to build pressure, the internal pump mechanism is worn. Disconnect the electrical harness and DEF lines from the pump module, unbolt it from the chassis bracket, and install a new DEF supply module.

7. 7

   Reassembly and Testing

   Reconnect the battery. Connect the CNH EST diagnostic tool, clear the active 19753 fault code, and run a manual DEF dosing override test to verify the system builds pressure and the pump speed normalizes.