P0255 — Injection Pump Fuel Metering Control A Intermittent (Cam/Rotor/Injector)

Diagnostic algorithm

1. Retrieve freeze frame and all stored codes. Note conditions when code set (engine temp, RPM, load).
2. Visually inspect the pump connector and harness for corrosion, bent pins, chafing, or repairs. Repair any obvious damage before further testing.
3. Check battery voltage and main engine grounds. Clean and tighten ground points and battery connections as needed.
4. Backprobe the pump control 'A' connector. With ignition ON and engine OFF, measure voltage at the supply pin and resistance of the actuator if accessible; compare to specs.
5. With a scan tool, command the fuel metering actuator while monitoring the actual signal. Look for proper response and stable duty cycle. Observe for intermittent loss or erratic duty.
6. Wiggle/shift harness and connectors while monitoring the live signal to reproduce intermittent behavior. Inspect any cover grommets or flex points for damage.
7. Use an oscilloscope to inspect waveform for correct PWM frequency and clean edges. Look for noise, dropouts, or voltage spikes.
8. If wiring and connector check good but signal still intermittent, substitute or bench-test the pump actuator (if serviceable) or replace injection pump assembly per manufacturer procedure.
9. If actuator and harness test good, consider PCM output test or reflashing as last resort — confirm with manufacturer diagnostics before replacing PCM.
10. After repairs, clear codes and road test under conditions similar to freeze frame. Re-scan to confirm code does not return.