Case IH 19745 – Engine Control Module (ECM) / Engine Control Unit (ECU): Maximum negative rail pressure deviation with closed pressure control valve exceeded

The engine's actual fuel rail pressure has dropped significantly below the target pressure requested by the ECM, even though the pressure control valve (PCV) has been commanded closed to build maximum pressure. This indicates a severe inability to build or maintain high-pressure fuel, usually caused by fuel starvation, excessive injector return leakage, or a faulty sensor.

• Tier 4b
• 770
• 970
• 1070
• 1090
• 1170
• 1175
• 1270
• 1370
• 1470

1. 1

   Monitor Rail Pressure Sensor (RPS) output voltage and check for a short to a low voltage line, which can cause falsely low pressure readings.

2. 2

   Verify the supplying state of the low-pressure fuel system (pre-supply pump and filters) to ensure adequate fuel delivery.

3. 3

   Check for excessive fuel return from the injectors (Leakage / Return Flow Test) to identify stuck-open injectors bleeding off rail pressure.

4. 4

   Evaluate the mechanical operating conditions of the high-pressure pump and the rail pressure regulator valve (RPRV).

1. 1

   Monitor rail pressure

   Connect a diagnostic scan tool to monitor target rail pressure versus actual rail pressure while cranking or running.

2. 2

   Inspect low-pressure fuel circuit

   Inspect the low-pressure fuel circuit. Replace clogged fuel filters and verify the pre-supply lift pump is delivering fuel at the correct specification.

3. 3

   Perform injector leak-off test

   Perform an injector leak-off (return flow) test. If one or more injectors are returning excessive amounts of fuel, they are bleeding rail pressure and must be replaced.

4. 4

   Inspect wiring harness

   Inspect the wiring harness to the Pressure Control Valve (PCV) and Rail Pressure Sensor for chafing, shorts to ground, or open circuits. Repair wiring as necessary.

5. 5

   Replace faulty components

   If the low-pressure supply is good, injectors are not leaking excessively, and wiring is intact, replace the faulty Pressure Control Valve or the High-Pressure Fuel Pump assembly.

6. 6

   Clear codes and test run

   Clear the ECM fault codes and test run the machine under load to verify rail pressure tracks the target pressure without deviation.