Case IH 19714 – Engine Control Module (ECM) / Engine ECU: Maximum positive deviation of rail pressure exceeded for tank lo detection

This code indicates that the actual fuel rail pressure is spiking significantly higher than the target pressure requested by the engine control module (positive deviation). The 'tank lo detection' portion means this over-pressure condition was triggered while the fuel tank level was low. When fuel levels are low, the fuel pickup tube can draw air into the low-pressure fuel system. Air in the system causes erratic pressure readings, prompting the fuel metering unit (FCA/M-Prop) to overcompensate and cause severe pressure spikes in the high-pressure common rail.

• Tier 4b
• Magnum
• Maxxum
• Farmall
• Puma
• Steiger
• N-Series Backhoe Loaders
• 580N
• 590N
• Skid Steers
• Compact Track Loaders
• TV380
• TR270
• Wheel Loaders
• 621F
• 721F

1. 1

   Verify the physical fuel level in the tank. Do not rely solely on the gauge, as a faulty sending unit may show fuel when the tank is actually empty or low enough to draw air.

2. 2

   Inspect the low-pressure fuel lines for air intrusion.

3. 3

   Check the primary fuel filter/water separator and the secondary fuel filter for clogging, debris, or water contamination.

4. 4

   Test the low-pressure supply pump (lift pump) to ensure it is delivering adequate volume and pressure to the high-pressure pump.

5. 5

   Inspect the wiring harness and connector at the fuel metering unit (FCA/M-Prop) on the high-pressure injection pump for damage or corrosion.

6. 6

   Check the fuel rail pressure sensor and its wiring on the fuel rail for shorts or opens.

7. 7

   Inspect the mechanical pressure relief valve (PRV) on the fuel rail to see if it has been forced open due to the pressure spike. Once a PRV pops, it often leaks and must be replaced.

1. 1

   Refuel and Bleed

   Fill the fuel tank to ensure the pickup tube is fully submerged. Bleed the low-pressure and high-pressure fuel systems completely to remove any trapped air.

2. 2

   Replace Filters

   Replace both the primary fuel filter/water separator and the secondary fuel filter to eliminate restrictions.

3. 3

   Clear Codes and Test

   Use a diagnostic tool (such as the Case EST) to clear the fault codes. Run the engine and monitor the actual vs. desired fuel rail pressure live data.

4. 4

   Replace the Fuel Metering Unit

   If the code returns and the rail pressure is still spiking (positive deviation), the fuel metering unit (FCA) is likely sticking and over-pressurizing the rail. Replace the metering unit.

5. 5

   Replace the Rail Pressure Sensor

   If the live data shows erratic or implausible pressure readings even when the engine is off, replace the fuel rail pressure sensor.

6. 6

   Replace the Pressure Relief Valve

   If the over-pressure event forced the PRV open, it will likely cause subsequent low-pressure codes (e.g., P0087) or hard starting. Replace the PRV if it is leaking fuel back to the return line.