New Holland DCU 19082 – DCU: Voltage supply 3 - Coolant control valve and reverting valve (UB3) electrical | Short to bat at UB3 with Key 15 off

The system has detected a short circuit to battery voltage (high) on the UB3 circuit (Voltage supply 3) when the ignition key is turned off. This specific circuit supplies power to the DEF (Diesel Exhaust Fluid) reverting valve (also known as the reductant purge control valve) and the DEF coolant control valve. The reverting valve is responsible for purging DEF back into the tank when the machine is shut down to prevent freezing.

• T6 series
• T7 series
• T8 series
• T9 series
• CR series
• CX series
• CR9090
• CX8080
• CX8090
• W-Series wheel loaders
• W190C
• W230C
• LM/Farmlift series telehandlers

1. 1

   Verify the Fault State: Use an Electronic Service Tool (EST) to check if the fault is currently active or stored.

2. 2

   Visual Inspection: Locate the DEF supply module (pump) and the coolant control valve (often mounted on the same support structure near the DOC/SCR muffler). Inspect the wiring harnesses and connectors for physical damage, chafing, bent pins, or corrosion.

3. 3

   Circuit Testing (UB3): Using a multimeter, test the UB3 circuit for a short to battery voltage when the key is off.

4. 4

   Component Isolation: Disconnect the reverting valve (at the DEF pump) and the coolant control valve one at a time. If the short-to-battery voltage disappears when a specific component is unplugged, that valve has an internal short and must be replaced.

5. 5

   Check for DEF Intrusion: Inspect the DEF pump module and connectors for DEF leaks. Crystallized urea can bridge electrical contacts and cause short circuits.

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the negative battery terminal.

2. 2

   Access the Components

   Locate the DEF supply module and coolant control valve assembly. You may need to remove protective shielding near the exhaust/DOC unit.

3. 3

   Repair Wiring (If Applicable)

   If the diagnostic checks revealed a chafed wire shorting to a power source, repair the wiring harness using OEM-approved sealed splices and heat shrink.

4. 4

   Replace the Faulty Valve

   If the Coolant Control Valve is shorted: Disconnect the coolant hoses (clamp them off to minimize coolant loss) and the electrical connector. Unbolt the valve from the bracket and install the new one. If the Reverting Valve is shorted: On many Bosch Denoxtronic systems used by FPT, the reverting valve is integrated into the DEF Supply Module (Pump). You will need to replace the entire DEF pump assembly. Disconnect the DEF suction, pressure, and return lines, unplug the electrical harness, and unbolt the pump.

5. 5

   Reassembly

   Reconnect all fluid lines, electrical connectors, and the battery.

6. 6

   Clear Codes and Test

   Connect the New Holland EST (Electronic Service Tool). Clear the DCU 19082 / P20A3 fault codes. Run a forced DEF dosing system test or a system purge test to verify the reverting valve operates correctly and the code does not return.