P0255 - Injection Pump Fuel Metering Control B Intermittent (Cam/Rotor/Injector)
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
The P0255 code is stored when the Engine Control Unit (ECU) detects an intermittent or erratic signal within the fuel metering control 'B' circuit of the injection pump. This typically applies to high-pressure diesel or GDI systems where fuel volume is regulated via a solenoid or control valve. The 'Intermittent' designation indicates that the fault is not constant, suggesting issues like frayed wiring, loose connectors, or a solenoid valve beginning to fail mechanically. The ECU monitors the duty cycle and current draw; if these values fluctuate outside defined parameters for brief intervals, the code is triggered and the vehicle often enters 'Limp home mode' to protect the fuel rail and pump components.
Possible Causes
Loose connection or corrosion in the fuel metering valve connector.
Damaged wiring harness (chafing or short to ground) in the metering control circuit.
Faulty fuel metering solenoid sticking intermittently.
Internal ECU failure or software glitch.
Symptoms
Recommended Solution
- Visual Inspection: Check the injection pump connector for corrosion or backed-out pins. Clean with contact cleaner.
- Wiring Harness Test: Inspect the harness between the pump and ECU for chafing. Perform a 'wiggle test' while measuring resistance (Ohms) to find intermittent breaks. Resistance should be stable (typically 1-5 Ohms for the coil).
- Signal Verification: Use an oscilloscope to verify the PWM (Pulse Width Modulation) signal to the valve. Standard multimeters are often too slow to catch intermittent drops.
- Component Test: Perform a bidirectional activation test of the fuel metering valve using a diagnostic scan tool.
- Replacement: If wiring is intact and ECU signals are correct, replace the fuel metering regulator/solenoid.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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