New Holland DCU 19172 – DCU: Cooling control valve short circuit to ground | P20A2 Vent valve (Reductant Purge Control Valve) - short circuit low

The electrical circuit controlling the DEF (Diesel Exhaust Fluid / Reductant) cooling control valve or purge vent valve has shorted to ground, meaning the voltage in the circuit is dropping to zero unexpectedly.

• T6 Series Tractors
• T7 Series Tractors
• T8 Series Tractors
• T9 Series Tractors
• CR Series Combines
• CR9090
• CX Series Combines
• CX8080
• CX8090
• Wheel Loaders
• W190B
• Telehandlers

1. 1

   Turn off the ignition switch and disconnect battery power before unplugging modules

2. 2

   Visually inspect the wiring harness routed between the DCU and the DEF cooling control valve for chafed insulation, bare wires touching the frame, or melted wire loom

3. 3

   Disconnect the harness at the valve and inspect the pins for corrosion, moisture, or damage

4. 4

   Perform a harness short test by checking for continuity between the valve's power supply wire and the machine's chassis ground with the valve and DCU disconnected

5. 5

   Perform a component short test by measuring resistance across the valve pins and checking for continuity between the power pin and the valve's metal housing

1. 1

   Isolate Power

   Disconnect the machine's battery to prevent electrical spikes.

2. 2

   Wiring Repair

   If the diagnostic checks revealed a chafed wire, cut out the damaged section, solder or use sealed heat-shrink butt connectors to splice in new wire, and wrap it in protective loom. Reroute the harness away from sharp edges or hot exhaust components.

3. 3

   Valve Replacement

   If the valve is internally shorted, prepare to catch any leaking fluid. Clamp off the engine coolant lines or relieve DEF system pressure. Disconnect the fluid hoses, unbolt the valve bracket, remove the faulty unit, install the new valve, and reconnect and secure the fluid hoses.

4. 4

   Reassembly

   Plug the electrical connector back into the valve.

5. 5

   Fluid Check

   Top off the engine coolant or DEF fluid if any was lost during the swap.

6. 6

   Clear Codes

   Reconnect the battery. Connect a diagnostic scanner (such as the CNH Electronic Service Tool) to clear the DCU 19172 / P20A2 fault codes.

7. 7

   Test Run

   Start the engine and let it reach operating temperature to ensure the DEF system initializes, the heater valve operates without throwing a code, and there are no fluid leaks.