P0256: Injection Pump Fuel Metering Control B Malfunction
The P0256 code indicates a malfunction in the fuel metering control circuit 'B' of the injection pump, which typically involves the cam, rotor, or injector components. This circuit controls the amount of fuel delivered to the engine based on demand. A fault can cause incorrect fuel metering, leading to performance issues. Common causes include a faulty fuel metering solenoid, wiring issues, or internal pump damage.
1. Most Common Causes
- Faulty fuel metering solenoid
- Open or shorted wiring in the metering control circuit
- Internal injection pump failure (cam, rotor, or injector damage)
- Corroded or loose electrical connectors
- Engine control module (ECM) issues
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine hard to start or no start
- Loss of power or poor acceleration
- Engine misfire or rough idle
- Excessive smoke from exhaust
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm P0256 and check for other codes.
Step 2: Visually inspect wiring and connectors for damage, corrosion, or looseness.
Step 3: Test the fuel metering solenoid resistance and compare to manufacturer specs.
Step 4: Check fuel pressure and volume to rule out fuel supply issues.
Step 5: If all else fails, perform a injection pump flow test or replace the pump.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. The vehicle may experience loss of power, stalling, or difficulty starting, which can be dangerous, especially in traffic.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Repair costs vary: a fuel metering solenoid replacement may be $200-$400, while a full injection pump replacement can exceed $1,500.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.