OBD Code P0255: Injection Pump Fuel Metering Control "A" High (Cam/Rotor/Injector)

Q: What are the symptoms of fault code P0255?

Black smoke from exhaust or excessive fuel smell, Rough idle or engine hesitation under acceleration, Reduced fuel economy and engine running overly rich

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What This Actually Means

In plain language — no jargon

The engine's fuel injection pump isn't controlling fuel delivery properly—it's running too rich or the pump's timing signal is too high. Think of it like a water faucet stuck in the open position; fuel is flowing more than it should.

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Symptoms You May Notice

3 known symptoms for this code

Black smoke from exhaust or excessive fuel smell

Rough idle or engine hesitation under acceleration

Reduced fuel economy and engine running overly rich

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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the fuel metering control signal (voltage or duty cycle) sent to the injection pump's cam, rotor, or solenoid. It expects this signal to stay within a specific range; when it reads consistently higher than the maximum threshold, it triggers a fault.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
Fuel Metering Control Voltage	0–5V (typical duty cycle 0–100%)	Signal exceeds maximum expected voltage or duty cycle
Pump Response Time	Within 50–200ms depending on strategy	Control signal remains elevated without proper modulation

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

Fuel injector/pump connector

Inspect and clean corroded or loose connectors on the fuel pump or injector solenoid; poor connections cause high control signals.

2

Engine control module (ECM) software

Update the ECM firmware to the latest calibration if available for your vehicle model.

3

Fuel metering solenoid or pump rotor

Replace the solenoid or rotor assembly if it's stuck or electrically failing and causing the high signal condition.

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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0255 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.

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How to Clear Code P0255

What happens after you fix the fault

Once the fault is repaired, P0255 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When

Fault has been diagnosed and repaired
You want to confirm the repair worked
Code appeared after a sensor was cleaned

⚠️ Do Not Clear When

Preparing for an emissions/PUC test
Root cause is still undiagnosed
Check engine light is flashing

Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.