New Holland DCU 19019 – DCU (Dosing Control Unit): Temperature sensor before catalyst (electrical) — signal high / Catalyst Temperature Sensor Circuit High

This fault indicates that the signal voltage from the upstream exhaust gas temperature sensor (located before the oxidation catalytic converter or SCR catalyst) is exceeding the maximum normal operating threshold. A 'signal high' condition almost always points to an open circuit, a disconnected sensor, a broken wire in the harness, or a completely failed sensor element.

• T6 series
• T7 series (T7.170 to T7.270)
• T8 series
• T6000 series
• W190B
• 721F-921F
• 580N EP
• 580SN
• 590SN
• Magnum series (235-340)
• Puma series
• Maxxum series

1. 1

   Visually inspect the temperature sensor upstream of the catalyst, checking the wiring pigtail and main harness connector for melted wires, chafing, or disconnected plugs.

2. 2

   Perform an open circuit check by disconnecting the sensor and measuring resistance across its pins with a multimeter; infinite resistance (OL) indicates the sensor is internally open and must be replaced.

3. 3

   Test the harness by turning the ignition ON (engine off) and measuring voltage at the harness-side connector to verify the presence of a 5V reference signal from the DCU. If missing, trace the harness back to the DCU for breaks or shorts.

4. 4

   Verify that the sensor ground circuit has continuity to the chassis or DCU ground.

1. 1

   Preparation

   Turn off the machine, remove the key, and allow the exhaust system to cool completely to avoid severe burns. Disconnect the negative battery terminal.

2. 2

   Removal

   Locate the upstream catalyst temperature sensor on the exhaust pipe just before the catalytic converter/SCR unit. Unplug the electrical connector and free the wire from any retaining clips. Using an appropriately sized wrench or O2/EGT sensor socket, carefully loosen and remove the sensor from the exhaust bung. (Penetrating oil may be required if the sensor is seized).

3. 3

   Installation

   Inspect the threads in the exhaust bung and clean them with a thread chaser if necessary. Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (avoid getting any on the sensor probe itself). Thread the new sensor in by hand to prevent cross-threading, then tighten to the OEM torque specification. Route the wiring pigtail away from direct heat sources and reconnect the electrical plug.

4. 4

   Verification

   Reconnect the battery. Turn the ignition on and use a diagnostic scan tool to clear the DCU 19019 / P0428 fault code. Start the engine and monitor the catalyst temperature data stream to ensure the sensor is reading correctly and the code does not return.