OBD-II Diagnostic Trouble Code
P0256 — Injection Pump Fuel Metering Control B Malfunction
P0256 indicates a malfunction in the injection pump fuel metering control B circuit, a second metering or timing control device on the injection pump. What control B refers to differs by manufacturer (often a second metering solenoid, a timing control or a pressure control valve), so the OEM wiring diagram is needed. The ECM has detected the circuit or the component is not operating within its expected electrical range.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Injection Pump Fuel Metering Control B Malfunction
Code
P0256
Category
Powertrain
Subsystem
Fuel
Truck-relevant
Yes
What this means for truckers
Stop within ~50 miles on a Cummins X15, Detroit DD15, PACCAR MX-13. Driving longer risks damaging adjacent components (turbo housing, head gasket, aftertreatment) and turning a $300 fix into a $3,000 fix.
Before you replace parts — try this first
P0256 on the Fuel system is most often open, shorted or corroded wiring or connector on the control b circuit — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Typical symptoms are the check-engine light, reduced power or derate, hard starting, rough idle and possibly excess smoke if fuel quantity or timing is not controlled correctly. Severe cases can cause stalling or a no-start.
Common causes
- CommonOpen, shorted or corroded wiring or connector on the control B circuit ($150–$600)
- CommonFailed control B solenoid or valve on the injection pump ($400–$1500)
- OccasionalInternal pump failure requiring injection pump replacement ($1500–$4500)
- RareECM driver or connector pin fault ($1200–$3500)
How to fix
Identify the control B component from OEM service information, then inspect its harness and connector.
When to use: Always first, since the component differs by engine.
Check solenoid resistance and the circuit for open, short to ground and short to voltage.
When to use: When there is no visible wiring damage.
Command the component with a scan tool and verify response in live data.
When to use: To confirm the component works before condemning the pump.
Replace the solenoid/valve or the injection pump as required.
When to use: When electrical tests show the component is out of spec or unresponsive.
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0200 — Injector Circuit Malfunction
- → P0201 — Injector Circuit Malfunction - Cylinder 1
- → P0202 — Injector Circuit Malfunction - Cylinder 2
- → P0203 — Injector Circuit Malfunction - Cylinder 3
- → P0204 — Injector Circuit Malfunction - Cylinder 4
Frequently Asked Questions
Can I drive with code P0256?
Drive with caution. P0256 is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix P0256 on a commercial truck?
Total repair cost ranges $150–$4500 depending on the root cause. The cheapest fix is usually the first one listed below — Open, shorted or corroded wiring or connector on the control B circuit — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0256 fail a DOT inspection?
P0256 itself doesn't automatically fail an inspection, but if the truck is in reduced-power mode (limp mode) at the time of inspection, it WILL be flagged. Most inspectors will note the check engine light but pass the truck if it's running and performance is normal. Fix it before a Level 1 inspection regardless.
What's the difference between P0256 and related codes?
P0256 is closely related to: P0200 (Injector Circuit Malfunction), P0201 (Injector Circuit Malfunction - Cylinder 1), P0202 (Injector Circuit Malfunction - Cylinder 2), P0203 (Injector Circuit Malfunction - Cylinder 3). These codes share the same subsystem (fuel) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0256 is set without the companions, the issue is more isolated.
How do I prevent P0256 from coming back after a repair?
For P0256 (Injection Pump Fuel Metering Control B Malfunction), prevention centers on the fuel system. Replace fuel filters at the OEM interval — don't stretch them. Use only diesel from high-volume fuel stops (avoid bottom-of-tank fuel at low-traffic stations). Add a water separator if you don't have one. After repair, prime the fuel system per the engine manual.