Case IH 3635 – Engine Control Unit (ECU): Fuel in Oil high pressure (FUEL IN OIL)

This code indicates that the crankcase pressure has exceeded normal limits due to an excessive engine oil level, specifically caused by fuel dilution (fuel leaking into the engine oil). When the oil level increases too much from fuel dilution, the pressure in the crankcase rises and eventually overcomes the tightness of the blow-by filter. To prevent engine damage, an electrically controlled venting valve in the crankcase is commanded to open.

• Case IH Steiger tractors (350 to 600 horsepower)
• Case IH Magnum tractors
• Case IH Farmall tractors
• Case IH Combines (5140, 6140, 7140, 7240, 8240, 9240 series)

1. 1

   Check Engine Oil Level: Pull the dipstick to verify if the engine oil is overfull.

2. 2

   Check for Fuel Dilution: Inspect the oil for the smell or visual presence of diesel fuel. Fuel dilution dramatically reduces oil viscosity and increases crankcase pressure.

3. 3

   Inspect the Crankcase Pressure Sensor: If the oil level is correct and there is no fuel in the oil, check the crankcase pressure sensor, its wiring harness, and all electrical connections for damage, corrosion, or loose pins.

4. 4

   Inspect the Crankcase Venting Valve: Verify that the electrically controlled venting valve is not mechanically blocked or stuck open, and check its wiring harness.

5. 5

   Fuel System Leakage Test: If fuel is confirmed to be in the oil, you must perform a fuel system leakage test to identify the source of the internal leak (e.g., leaking fuel injectors, high-pressure fuel pump seal failure, or rail leakage).

1. 1

   Verify Oil Condition

   Check the engine oil level and condition. If fuel dilution is present, proceed to Step 2. If the oil level is normal and uncontaminated, skip to Step 5.

2. 2

   Diagnose the Fuel System

   Perform a high-pressure fuel system leakage test to isolate the source of the fuel entering the crankcase. Common culprits include leaking electronically controlled injectors or a leaking high-pressure fuel pump.

3. 3

   Repair the Leak

   Replace the faulty fuel injectors, high-pressure pump, or leaking rail components as identified during the leak test.

4. 4

   Service the Oil

   Drain the contaminated engine oil, replace the engine oil filter, and refill the crankcase with the correct specification and volume of fresh engine oil.

5. 5

   Electrical/Sensor Testing

   If the oil was not overfull, the fault is likely electrical. Inspect the wiring and connectors between the ECU and the crankcase pressure sensor. Repair any damaged wiring or broken connector locks.

6. 6

   Replace Defective Sensors/Valves

   If the wiring is in good condition but the fault persists, replace the crankcase pressure sensor or the crankcase venting valve.

7. 7

   Clear Codes

   Use the Electronic Service Tool (EST) to clear the fault codes and run the engine to verify the repair.