New Holland NH 3112 – Engine Control Unit (ECU) / EDC: Rail pressure Min / Max. error - SOURCE HIGH

The electronic signal voltage returning from the fuel rail pressure sensor to the controller is exceeding the maximum expected threshold. This typically indicates a short to battery (high source) in the sensor wiring, a failed sensor, or an actual extreme overpressure condition in the Bosch CP3 common rail fuel system.

• T4
• T5
• T6
• T7
• T8
• T9
• T4.105
• T5.115
• T6.160
• T7.250
• T8.390
• CR series
• CR8.90
• CR9.90

1. 1

   Inspect the wiring harness and the 3-pin connector at the fuel rail pressure sensor for chafed wires, melted insulation, or corrosion (checking for a short to power source).

2. 2

   Verify that the low-pressure fuel supply to the CP3 pump is adequate and that the fuel filters are not restricted.

3. 3

   Using the CNH Electronic Service Tool (EST), check the Pulse Width Modulation (PWM) output of the CP3 pump (should be a minimum of 3% at engine idle and a maximum of 24% at full load).

4. 4

   Perform a leak-off test if the PWM output is above 24% to physically check for excessive return flow from the overpressure (relief) valve in the fuel rail or from the injector/transfer tubes.

1. 1

   Safely Prep the Machine

   Turn off the engine, remove the key, and disconnect the battery to prevent electrical shorts while working on the ECU harness. Ensure the high-pressure fuel system has depressurized.

2. 2

   Test the Circuit

   Disconnect the rail pressure sensor. Use a multimeter to check the signal wire for a short to 12V/battery voltage. If a short is present, trace the harness back to the Engine ECU and repair the damaged wiring.

3. 3

   Replace the Sensor

   If the wiring tests perfectly, the rail pressure sensor has likely failed internally, causing it to output maximum voltage. Remove the old sensor from the fuel rail and install a new OEM sensor. Torque to manufacturer specifications.

4. 4

   Inspect the Relief Valve

   If the sensor was not the issue, inspect the rail pressure relief valve. If it is mechanically stuck or leaking excessively (as found in the leak-off test), replace the relief valve.

5. 5

   Address the CP3 Pump

   If the system is genuinely over-pressurizing due to a failed fuel metering unit on the high-pressure pump, the CP3 pump assembly will need to be replaced.

6. 6

   Finalize

   Reconnect all electrical connections, bleed the low-pressure fuel system if lines were opened, reconnect the battery, and use a diagnostic tool to clear the NH 3112 fault code. Run the engine and verify that rail pressure tracks target pressure without throwing the code.