Case IH 19038 – DCU (Dosing Control Unit): Sensor supply 2 (5V internal; for UREA pressure sensors) | Supply voltage too low | P204C Reagent - pressure sensor - short circuit low.

The 5-volt reference circuit (Sensor Supply 2) provided to the Urea (DEF) pressure sensor has dropped below the acceptable threshold. This is typically caused by a short circuit to ground, a short to a low-voltage source, or an internal failure within the sensor or the control module.

• Tier 4a
• Tier 4 Final agricultural equipment
• Case IH Magnum 235 - 340 (Series 4)
• Case STX Steiger tractors (350 to 600 HP)
• Case IH Puma series

1. 1

   Inspect the urea pressure sensor wiring harness for any chafing, bare wires, or a short circuit to ground

2. 2

   Check other sensors that may share the 'Sensor Supply 2' 5V reference circuit (such as the rail pressure sensor) for a short circuit to ground

3. 3

   Inspect the DEF pump module and DCU wiring connectors for corrosion, moisture intrusion, or physical damage

4. 4

   Disconnect the urea pressure sensor to see if the 5V reference voltage returns on the harness side, which would indicate an internal sensor short

5. 5

   If no short circuit is found in the wiring or sensors, test the DCU for an internal failure using a known good replacement controller

1. 1

   Power Down

   Turn off the machine and locate the DEF supply module/pump assembly (often mounted near or inside the DEF tank).

2. 2

   Disconnect and Test

   Disconnect the electrical connector for the urea pressure sensor. Turn the key to the ON position (engine off) and use a multimeter to measure the voltage at the 5V reference pin on the harness side.

3. 3

   Sensor Replacement

   If the voltage reads approximately 5V with the sensor unplugged, the sensor has an internal short. Because the urea pressure sensor is often integrated into the DEF supply module/pump assembly, you may need to replace the entire DEF pump module or DEF head unit.

4. 4

   Harness Repair

   If the voltage remains low with the sensor unplugged, trace the wiring harness back to the DCU. Look for pinched wires or rubbed insulation causing a short to the chassis. Repair or replace the damaged wiring harness section.

5. 5

   Module Replacement

   If the wiring tests perfectly and the 5V supply is still missing directly at the DCU pins, replace the Dosing Control Unit (DCU).

6. 6

   Clear Codes

   After replacing the faulty component or repairing the wire, clear the fault codes and run the machine to verify the DEF system builds pressure and the code does not return.