Iveco 155 – Engine Control Unit (ECU) / Electronic Diesel Control (EDC): Fuel pressure in the rail below the minimum allowable

The high-pressure fuel system is failing to build or maintain the commanded pressure in the common rail. When the actual rail pressure drops significantly below the commanded pressure, the engine control unit triggers this code, which can result in a flashing injector light, stalling under load, rough idling, or a complete no-start condition.

• Iveco Daily
• Iveco Stralis
• Iveco Tector
• Iveco Massif

1. 1

   Check fuel level and quality to ensure the fuel is not aerated, contaminated, or gelling.

2. 2

   Inspect the primary and secondary fuel filters for restrictions (a clogged filter is the most common cause of low supply pressure).

3. 3

   Test the low-pressure system (lift pump) to verify it is supplying adequate volume and pressure to the high-pressure fuel pump (HPFP).

4. 4

   Inspect fuel lines, fittings, and seals for cracks or loose connections that could introduce air into the system.

5. 5

   Monitor rail pressure sensor data using a diagnostic scanner to compare Commanded Rail Pressure versus Actual Rail Pressure. Check sensor voltage with the engine off (should read near 0 bar / approx. 0.5V).

6. 6

   Perform an injector return flow (leak-back) test to check for excessive fuel leaking back to the tank from worn injectors.

7. 7

   Test the fuel pressure regulator (MPROP / ZVC) duty cycle (PWM signal) to ensure the valve is not stuck open or mechanically failing.

8. 8

   Inspect the mechanical pressure relief valve by disconnecting the leak-off line for the common rail while cranking to see if fuel is escaping (indicates a stuck open valve).

1. 1

   Resolve Supply Issues

   If the fuel filter is restricted, replace the filter and prime the fuel system. If the lift pump is failing, replace it.

2. 2

   Fix Leaks

   Repair or replace any cracked low-pressure fuel lines or leaking high-pressure fittings.

3. 3

   Replace Faulty Injectors

   If the return flow test reveals that one or more injectors are leaking excessive fuel back to the return line, replace or rebuild the affected injectors.

4. 4

   Replace the Fuel Pressure Regulator

   If the metering valve/regulator on the HPFP is stuck or electrically faulty, replace the regulator.

5. 5

   Replace the High-Pressure Fuel Pump (HPFP)

   If the low-pressure supply is good, there are no leaks, the injectors are sealing, and the scanner shows the HPFP cannot hit the target pressure when commanded, the HPFP is internally worn and must be replaced.

6. 6

   Clear Codes and Road Test

   After repairs, use a diagnostic tool to clear the 0155 fault code. Test drive the vehicle under load to ensure the actual rail pressure matches the commanded pressure without dropping.