Comprehensive diagnostic guide for OBD-II Code P0255

Fuel pump measurement/control circuit - Intermittent (Cam/Rotor/Injector) / Fuel pump secondary circuit intermittent

Overview

• DTC family: P-codes are Powertrain/OBD-II codes. They are part of the diagnostic trouble codes used by on-board systems to indicate emissions-related and powertrain issues.

  • According to the OBD-II overview, DTCs are generated when the on-board diagnostic system detects parameters out of expected ranges or detects intermittent faults in powertrain controls.

• Specific mapping for P0255: The open-source definition provided describes P0255 as which translates roughly to an intermittent fault in the "fuel pump measurement/control circuit" related to cam/rotor/injector. This wording indicates an intermittently failing signal or control path associated with the fuel pump or injector pump control circuit. ")

• Note on terminology consistency: OEMs may describe P0255 differently in service literature. maps P0255 to an intermittent fault in the fuel pump control/metering circuit. Always check the vehicle-specific service information for exact wording and wiring diagrams. If you see conflicting descriptions in the work you perform, document both perspectives and validate with live data and wiring checks.

Symptoms

• Engine cranks but does not start, or is difficult to start
• Intermittent no-start condition, sometimes starting after multiple attempts
• Engine stalls or hesitates during idle or low-speed operation
• Long crank times before engine starts
• Check Engine Light with P0255 stored or pending
• In some cases, fuel pump operation or signal seems inconsistent, with occasional normal starts

What this code likely indicates

• An intermittent fault in the fuel pump control circuit (the secondary circuit that powers or signals the fuel pump relay/ pump) or the injector pump measurement/control path. The problem can originate in the relay/signal circuit, wiring/connectors, the PCM/ECU output, or the pump itself. Because the fault is intermittent, you may not see the code every time you scan, but live data and fuel pressure observations during crank can reveal the failure mode.

Probable Causes

• Fuel pump relay or the pump control circuit intermittently failing to energize (including relay contacts, fuse, harness to relay/pump): ~40-60%
• Wiring harness/connectors to the fuel pump, relay, or injector pump showing corrosion, looseness, or pinching leading to intermittent signal/ground issues: ~15-25%
• PCM/ECU output or control circuit fault (intermittent driver signal to the relay or pump): ~10-20%
• Mechanical fuel pump issues or clogged/restricted supply (pump itself, intake screen, or filter): ~5-10%
• Electrical supply concerns (low battery voltage, alternator issues, or wiring- voltage drop under load): ~5%
• Software/Calibration or documentation in OEM service bulletins affecting fuel control logic: ~5%

Safety Considerations

• Fuel system work can pose fire and explosion hazards. Relieve fuel system pressure following the manufacturer's procedure before disconnecting lines or servicing the pump, lines, or injectors.
• When performing live tests (fuel pump energizing, voltage checks at the pump), keep ignition off as required and follow safe electrical practices. Use proper PPE and have a fire extinguisher available.

Diagnostic Approach

1) Confirm the DTC and data context

• Confirm P0255 is present (not history-only), and review freeze-frame data if available to understand engine load, RPM, temperature, fuel system status at the time the fault occurred.
• Check for related/auxiliary codes (e.g., other fuel system codes, sensor codes) that could point to the same intermittent fault path or to a broader system issue.

2) Visual and basic electrical checks

• Inspect fuses and relays related to the fuel pump circuit and its control (fuel pump relay, any ECM/PCM power relay if applicable). Look for signs of corrosion, heat damage, or poor connections.
• Inspect wiring harnesses to the fuel pump, pump relay, and related connectors for chafing, pin-fit, bent pins, or water exposure. Pay special attention to grounds and the pump power feed.
• Check battery condition and charging system; ensure stable voltage under cranking. Low voltage can cause intermittent fuel pump operation.

3) Live data and circuit integrity checks

• With a scan tool, monitor the fuel pump control signal/output (if the vehicle provides a live signal for the pump or a relay coil control). Observe whether the PCM is commanding the pump during cranking and whether the relay is energizing consistently.
• Measure voltage at the fuel pump connector (in the harness or at the tank) during cranking and under idle. Compare pump supply voltage to expected value (typically near battery voltage when energized). Look for voltage drop or intermittent loss.
• Check the ground circuit for the fuel pump and the fuel pump relay. A high-resistance ground can cause intermittent pump operation.

4) Fuel pressure testing

• Attach a fuel pressure gauge and observe fuel pressure during cranking and after start. If pressure remains low or fluctuates during cranking while the PCM attempts to energize the pump, suspect the pump circuit or the pump itself.
• If possible, compare to manufacturer spec for fuel pressure at cranking and at idle. Note that some systems regulate pressure differently during cranking vs. running.

5) Relay and circuit testing

• Swap the fuel pump relay with a known-good relay of the same type to determine if the fault is relay-related.
• If allowed by OEM practice, bench-test the pump by applying a controlled 12V supply to the pump directly (with appropriate safety precautions) to verify pump operation independent of the control circuit. If the pump runs when directly energised but not via the vehicle's control circuit, focus on the control signal, wiring, or PCM.

6) Pump and filter assessment

• Inspect the fuel filter(s) and screen in the fuel tank (if accessible). A clogged filter can produce symptoms that mimic intermittent pump issues.
• If pump testing indicates poor performance or failure to draw fuel, consider pump replacement.

7) PCM/ECU considerations

• If the pump relay and wiring test good and fuel pressure is inconsistent with operation of the control circuit, consider PCM/ECU fault or software/firmware related issues. This is more likely if voltage and control signals are inconsistent with expected patterns. Check for OEM service bulletins or recalls that address fuel control logic for the specific vehicle.

8) Verification

• After repairing or replacing suspected components (relay, wiring, pump, grounds), clear the codes and perform a controlled test drive. Re-check for DTCs and monitor fuel pressure and pump control data to confirm the issue is resolved.
• If the code returns intermittently, consider additional data logging for a longer period or a more extensive vibration/road-test to provoke the intermittent condition, along with a re-check of grounds and harness routing.

Common Repairs

• Replace or repair the fuel pump relay, or repair the relay control circuit (including fuse and wiring) if intermittent energizing is observed.
• Repair or replace damaged wiring/connectors to the pump relay and pump, and fix poor grounds or voltage-reduction issues.
• Replace the fuel pump if it fails to deliver consistent pressure or show signs of failure during direct testing.
• Replace or repair the fuel filter or screen if restriction is found.
• Address PCM/ECU issues if persistent control signal problems are observed after wiring and relay checks; apply updated software/firmware or service bulletins as indicated by OEM documentation.
• Ensure all repairs are validated with test drive and by confirming DTCs are cleared and not reoccurring.

OEM variation and documentation caveats

• P0255 interpretations can vary by OEM; some sources indicate "intermittent fuel pump/pressure control" faults tied to the pump control circuit, while others describe it specifically as an intermittent fault in the injector pump metering/control path. When diagnosing, cross-reference with the vehicle's service information for exact circuit diagrams, pinouts, and test procedures. If you encounter conflicting definitions, document both and rely on live data (voltage, current, and fuel pressure) to determine the actual fault path.

What to document in the repair log

• DTC present and any freeze-frame data
• Symptom description and vehicle operating conditions (engine cold/hot, load, RPM, speed)
• All tests performed with results (fuses, relays, wiring continuity, pump voltage, fuel pressure)
• Any parts replaced or repaired (relay, wiring harness, fuel pump, fuel filter)
• PCM/ECU-related observations (live data, software version, any TSBs)
• Final vehicle test outcome and status of DTCs after repair

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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