CLAAS 772Fh – ECU: Fuel Pressure Sensor Input Voltage Fault

The Engine Control Unit (ECU) has detected an abnormal input voltage signal from the fuel pressure sensor located in the common rail. This condition typically indicates an open circuit, a short circuit to ground, or a short circuit to positive. The ECU relies on accurate voltage signals from this sensor to monitor and regulate high-pressure fuel delivery; without it, optimal combustion and fuel system management are compromised.

• AXION 960
• AXION
• AVERO
• Tractors with AGCO Power engines

1. 1

   Visually inspect the fuel pressure sensor's electrical connector and wiring harness for any signs of damage, corrosion, or loose connections

2. 2

   Perform a Wiggle Test: While monitoring the signal voltage, gently wiggle the sensor connector and wiring harness to check for intermittent connections or voltage fluctuations

3. 3

   Check for other fault codes using a diagnostic scanner that could point to a broader electrical or fuel system issue

4. 4

   Perform a Reference Voltage Test: Disconnect the sensor and, with the ignition on (engine off), measure the voltage between the 5V reference wire and a known good ground (should be approximately 5.0V)

5. 5

   Perform a Static Signal Voltage Test: Reconnect the sensor, back-probe the signal wire with ignition on (engine off). The voltage should be approximately 0.5V

6. 6

   Perform a Dynamic Signal Voltage Test: Start the engine. At idle, the signal voltage should be between 1.0V and 1.5V and increase smoothly as the engine is revved. A voltage stuck at 0V or 5V, or erratic behavior, indicates a faulty sensor

1. 1

   Confirm fault and inspect

   Verify the fault code is active or stored using a diagnostic tool. Complete all visual and electrical diagnostic checks to isolate the cause to either the wiring or the sensor.

2. 2

   Repair wiring issues

   If the reference voltage test fails or the wiggle test reveals fluctuations (wiring/connector cause), repair or replace the damaged wiring harness or connectors. Clear the fault codes and re-test.

3. 3

   Replace fuel pressure sensor

   If the wiring is sound but the signal voltage tests fail (sensor cause), relieve the pressure from the fuel rail, remove the old sensor, and install a new one torqued to the manufacturer's specification. Reconnect the electrical connector.

4. 4

   Clear codes and verify repair

   Clear the fault codes from the ECU. Start the engine and use a diagnostic tool to monitor live fuel pressure data to ensure the new sensor is functioning correctly. Check for fuel leaks around the new sensor.