Case IH t73 – PCU (Pump Control Unit): Engine Overspeed, Data Valid But Above Normal Range

The engine speed has exceeded the overspeed warning limit (typically detected when engine speed exceeds 2600 RPM). The sensor is reading valid data, but the RPM is dangerously high.

• MXM
• Case IH MXM Series Tractors (MXM 120, 130, 140, 155, 175, 190)
• Case IH Steiger

1. 1

   Rule out Operating Error: Interview the operator. The most common cause of this code is downhill travel with a heavy load, where the wheels drive the engine past its governed RPM limit.

2. 2

   Check for Engine Runaway Conditions: Inspect the engine for signs of a runaway condition where the engine accelerates without operator input. This is usually caused by combustible fluids entering the cylinders.

3. 3

   Inspect Fuel Injectors: Check for faulty fuel injectors that may be leaking excess fuel into the cylinders.

4. 4

   Inspect the Intake/Turbocharger: Check for engine oil leaking into the intake manifold (often caused by a blown turbocharger seal), which the engine will burn as unregulated fuel.

5. 5

   Test the Engine Speed Sensor: If the engine is not actually overspeeding but the code is active, inspect the camshaft/crankshaft engine speed sensor and its wiring harness for shorts, corrosion, or erratic data.

1. 1

   Operator Error Resolution

   If the overspeed was caused by downhill travel, clear the fault code from the PCU. Advise the operator on proper gear selection and engine braking. Test drive the tractor to ensure the code does not return.

2. 2

   Wiring Harness Inspection

   If the code is a false positive, disconnect the engine speed sensor. Use a multimeter to check the continuity of the wiring harness back to the PCU. Look for resistance indicating dirty/corroded terminals or a short to ground. Repair the harness if necessary.

3. 3

   Sensor Replacement

   If the wiring is intact but the PCU is receiving erratic RPM spikes, replace the Engine Speed Sensor.

4. 4

   Mechanical Leak Repair (Runaway)

   If the engine is genuinely overspeeding on its own, immediately shut down the machine. Diagnose the source of the fluid leak. Replace any leaking fuel injectors or replace the turbocharger if the oil seals have failed.

5. 5

   Calibration

   After replacing the sensor or mechanical components, use the tractor's H-Menu or an electronic diagnostic tool to clear the PCU memory and perform an Engine Speed Sensor calibration.