CLAAS 7788h – ENG (A15): Fuel Pressure Sensor Reference Voltage High

The Engine Control Unit (ENG A15) has detected an anomaly in the 5-volt reference voltage circuit supplied to the common rail fuel pressure sensor. The 'High' designation indicates the voltage is unexpectedly elevated. This condition prevents the sensor from accurately measuring fuel pressure and can be caused by a short circuit, an open circuit, a failing sensor, or an internal ECU fault.

• Arion 410
• Arion 420
• Arion 510
• Arion 520
• Arion 530
• Arion 640
• Arion 500 Series
• Arion 600 Series
• Lexion
• Jaguar

1. 1

   Visually inspect the wiring harness and connectors between the ECU and the common rail fuel pressure sensor for chafing, corrosion, or loose connections

2. 2

   Verify reference voltage: Disconnect the sensor, turn ignition ON (engine off), and measure voltage between the reference pin and ground on the harness side. It should be a steady 5.0V (4.5-5.1V). 0V indicates an open/short to ground, while high/low voltage indicates an ECU power supply issue

3. 3

   Check ground circuit: With the connector disconnected, measure resistance between the harness ground pin and the battery negative terminal. It should be less than 0.5 ohms

4. 4

   Inspect signal wire: Check for a short circuit between the signal wire and the reference voltage wire or ground wire

5. 5

   Perform a wiggle test: Gently wiggle the wiring harness and connectors while monitoring the reference voltage to check for intermittent connections

1. 1

   Repair wiring and connectors

   If diagnostic checks reveal wiring issues, repair or replace the damaged sections. Ensure all connections are clean, tight, and secure.

2. 2

   Replace fuel pressure sensor

   If wiring and reference voltage are correct, the sensor is likely faulty. Relieve fuel system pressure, replace the fuel pressure sensor, torque to manufacturer specifications, and reconnect.

3. 3

   Replace Engine Control Unit (ECU)

   If the reference voltage is incorrect but the wiring is in good condition, the ECU may be faulty. ECU replacement and programming must be performed by a qualified technician.