P0257

Universal

Injection Pump Fuel Metering Control B Low (Cam/Rotor/Injector)

Definition source: General OBD-II reference catalog

Definition verification: Not independently verified for display.

Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium

Medium Severity

The engine computer has detected a low condition associated with injection-pump fuel metering control B. This system regulates fuel delivery; the exact controlled component and monitoring method depend on the vehicle. The code does not by itself prove that the pump or another part has failed. If fuel metering is affected, the engine may run poorly, lose power, stall, or be difficult to start.

Report an error with this code

⚠️ Before You Begin (Safety First)

If the engine stalls, loses substantial power, or runs too roughly to control the vehicle safely, stop driving and arrange assistance. Do not loosen fuel-injection lines: some systems operate at very high pressure and can cause serious injury. If fuel is leaking, shut the engine off and do not drive the vehicle.

Common Symptoms

The check-engine light may be on, with no noticeable change in how the vehicle runs.
Hard starting or extended cranking may occur if the detected condition interferes with fuel metering.
Rough running or hesitation may occur if fuel delivery is not controlled as intended.
Reduced power or poor acceleration may occur, and the engine may enter a limited-power mode on some vehicles.
The engine may stall if the fault significantly disrupts fuel metering.

Common Causes

A damaged, loose, corroded, or poorly connected wire or connector in the fuel metering control B circuit.
A circuit supply, ground, or connection problem that produces a low electrical or control condition.
A fault in the metering control component or actuator identified as control B for that vehicle.
An injection-pump or related fuel-system problem affecting the control system's operation.
A control-module or driver fault, considered only after circuit and component checks.

Diagnostic Steps

Record the code and any other stored codes before clearing anything; related codes can help narrow the affected system.
With the engine off, visually inspect accessible wiring and connectors associated with the injection-pump fuel metering system for looseness, damage, corrosion, or rubbing.
Check the vehicle's service information to identify control B and any safe owner-level inspection points; do not assume its location or wiring from another vehicle.
If the code returns or symptoms are present, arrange vehicle-specific electrical and scan-data testing rather than replacing the pump based on the code alone.
Do not loosen injection lines or probe unfamiliar circuits; leave high-pressure fuel-system and specialist electrical tests to a qualified technician.

When to Call a Professional

Use service information for the exact model, year, and engine to identify control B and its circuit. A technician can review related codes and scan data, inspect connectors and wiring, and test the circuit, power, grounds, and control response using the vehicle-specific procedure. Check the electrical system before condemning the injection pump or metering component.

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Commonly Asked Questions

Does P0257 confirm that the injection pump has failed?

No. It identifies a low condition associated with fuel metering control B, but wiring, connections, the control component, related fuel-system operation, or a control-module circuit may be involved. Testing is needed before choosing a repair.

Does “Low” mean the fuel pressure is low?

Not necessarily. The wording describes a low condition associated with the control B system; it does not, by itself, establish that fuel pressure is low.

Can I keep driving with this code?

That depends on how the engine runs. If it stalls, loses substantial power, or becomes difficult to control, stop driving and arrange assistance. Do not drive with a fuel leak.

What does control B refer to?

Its exact meaning and component depend on the vehicle's model, year, and engine. Service information is needed to identify the applicable control circuit or component.

Browse Available Code Guides

Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.