OBD-II Code P0256 — What It Means & How to Fix It

What Does This Error Mean?

P0256 indicates a malfunction in the injection pump fuel metering control circuit on Bank B. The engine computer can't communicate properly with the Bank B fuel metering solenoid. This is a diesel-engine code — it doesn't apply to standard gasoline vehicles. Symptoms include rough running, excessive exhaust smoke, hard starting, and reduced power. This needs proper diagnosis — incorrect fuel delivery shortens engine life.

Affected Models

All diesel vehicles 1996+
Common in diesel V8 and V10 trucks
Common in Ford Power Stroke V8 diesels
Common in Duramax V8 diesel engines
Common in high-mileage diesel pickups

Common Causes

Failed Bank B fuel metering solenoid inside the injection pump
Open or shorted electrical circuit to the Bank B solenoid
Poor connector contact at the injection pump Bank B terminal
Injection pump internal wear causing Bank B metering to fail
ECM fault affecting the Bank B control output circuit

How to Fix It

Pull all stored codes with a scanner. If you only see P0256 and no Bank A codes, the fault is isolated to the Bank B side. This is important — it means half the pump may be fine.

Write down every code present. The full list is your roadmap for diagnosis.
Visually inspect the injection pump wiring harness and connector on the Bank B side. Look for damage, corrosion, or loose terminals. This is the most common and cheapest cause of this code.

Sometimes cleaning and firmly re-seating the connector resolves the fault entirely.
Use a multimeter to check for continuity and proper voltage on the Bank B metering solenoid circuit. Compare readings to your vehicle's service manual specs.

An open circuit (infinite resistance) means a broken wire; voltage where there shouldn't be any means a short.
Replace the diesel fuel filter if it's overdue. Low fuel supply pressure can stress the metering system on both banks and trigger faults even when the solenoids themselves are okay.

This is cheap and worth doing regardless — a clogged filter harms the whole fuel system.
If electrical checks pass and the fault persists, take the vehicle to a diesel specialist. The Bank B solenoid assembly may need replacement, or the pump may need professional bench testing.

Some diesel injection pumps allow solenoid replacement without replacing the whole unit — ask your shop.

When to Call a Professional

A P0256 on Bank B means only one side of the engine's fuel system is affected. This requires a diesel specialist with the ability to monitor per-bank injection data live. Don't assume the entire pump is bad — get the specific Bank B circuit diagnosed first. Repairs range from $100 for a connector fix to $2,500 for a full pump replacement.

Frequently Asked Questions

What's the difference between P0251 and P0256?

Both are metering control malfunction codes, but they refer to different cylinder banks. P0251 is a Bank A fault (the side of the engine containing cylinder 1). P0256 is a Bank B fault (the opposite side). If you have both codes at the same time, the problem is more likely shared — such as fuel pressure or a wiring issue common to both sides.

Will P0256 affect my fuel economy?

Yes, often significantly. If Bank B is over-fueling, you'll use more fuel than normal and likely see black exhaust smoke. If it's under-fueling, that bank of cylinders may be running lean, causing rough idle and power loss. Either way, fuel economy suffers until the fault is corrected.

How much does it cost to fix P0256?

Wiring or connector repair: $100–$400. Bank B solenoid replacement: $200–$700 depending on the pump design. Full injection pump replacement: $1,000–$2,500 installed. Diagnosis alone at a diesel shop: $100–$200. Always diagnose before replacing expensive parts.