New Holland 3909 – Engine Control Unit (ECU): High pressure in crankcase

Pressure inside the engine block has exceeded the acceptable threshold. This condition is typically caused by a restriction in the crankcase ventilation system (clogged blow-by filter), fuel leaking into the engine oil (fuel dilution), or excessive combustion blow-by due to cracked piston rings.

• CR combines
• TX combines
• T5 series tractors
• T8 series tractors
• telehandlers

1. 1

   Inspect the crankcase breather/blow-by filter for clogs (most common cause of high crankcase pressure).

2. 2

   Check the engine oil level on the dipstick; an abnormally high level indicates fuel dilution.

3. 3

   If fuel dilution is suspected, check the high-pressure fuel rail, injectors, and high-pressure pump for internal leaks.

4. 4

   Observe the crankcase pressure sensor (CrCsP_pSens) measuring channel with a diagnostic tool at engine standstill. If the value is out of limits when the engine is off, the sensor is likely defective.

5. 5

   Evaluate the engine for a drop in power output or abnormal exhaust smoke, which indicates cracked or worn piston rings allowing combustion gases into the crankcase.

1. 1

   Replace blow-by filter

   If the blow-by filter is clogged, remove the old blow-by filter housing/element and install a new one.

2. 2

   Replace crankcase pressure sensor

   If the sensor reading is implausible at standstill, disconnect the wiring harness, check for proper vehicle supply voltage, and replace the defective crankcase pressure sensor.

3. 3

   Repair fuel leak and replace oil

   If fuel is found in the oil, isolate and replace the leaking fuel system component (e.g., leaking injectors or high-pressure pump seals). Drain the contaminated engine oil, replace the oil filter, and refill with fresh lubrication oil.

4. 4

   Overhaul engine

   If piston rings are cracked, a major engine overhaul is required to replace the piston rings and restore proper cylinder sealing.