P0256 Code - Injection Pump Fuel Metering Control 'B' Malfunction
Quick Answer
This fault code is stored in the Engine Control Module (ECM) when the system cannot correctly control the fuel pressure. Common causes include Faulty Fuel Pump, Fuel Pump harness is open or shorted, Fuel Pump circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- P0256 indicates Injection Pump Fuel Metering Control 'B' Malfunction.
- Common causes
- Common causes include Faulty Fuel Pump, Fuel Pump harness is open or shorted, Fuel Pump circuit poor electrical connection.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Code P0256 Description
Normally manufacturers will support data parameters for actual and desired fuel pressure.
A number of issues may cause this fault code to be set such as a faulty fuel rail pressure sensor, a mechanical fault with a fuel inlet metering valve could cause the valve to become stuck. An electrical fault such as an open circuit in the fuel inlet metering valve on a system with a normally closed valve will also cause this situation. A short circuit on the control wire of a normally open fuel pressure regulator will also cause this fault.
A fault in the fuel injector return system will cause the fuel pressure to be lower than expected. This causes fuel from the high-pressure circuit to be leaked back to the low-pressure circuit. A faulty maximum pressure relief valve will also cause this situation.
The high-pressure pump should also be tested to ensure it is capable of delivering the required volume of fuel.
What are the Possible Causes of the DTC P0256?
- Faulty Fuel Pump
- Fuel Pump harness is open or shorted
- Fuel Pump circuit poor electrical connection
- Faulty Engine Control Module (ECM)
How to Fix the DTC P0256?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0256 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
Need more information about the P0256 code?
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Information for Specific Makes
- P0256 Mercedes-Benz — Injection Pump Fuel Metering Control 'B' Malfunction
Frequently Asked Questions about P0256 Code
1. What are the common symptoms of OBDII code P0256?
- Common symptoms include reduced engine performance, rough idling, difficulty starting the vehicle, and potentially stalling while driving.
2. What can cause the Injection Pump Fuel Metering Control 'B' Malfunction (P0256) code to appear?
- The code P0256 can be triggered by issues such as a faulty fuel injector, a clogged fuel filter, a malfunctioning fuel pump, or wiring problems in the fuel metering control circuit.
3. How serious is the P0256 code?
- The P0256 code should be addressed promptly as it can lead to poor engine performance, reduced fuel efficiency, and potential engine stalling, which can be dangerous.
4. Can I still drive my vehicle with the P0256 code present?
- It is not recommended to drive your vehicle with the P0256 code active, as it can lead to further damage to engine components and potentially leave you stranded on the road.
5. How can I diagnose the cause of the P0256 code?
- Diagnosing the P0256 code typically involves using a scan tool to check for other related codes, inspecting fuel system components for issues, and testing the fuel metering control circuit for proper operation.
6. What are some possible repair tips for fixing the P0256 code?
- Repair tips may include replacing a faulty fuel injector, cleaning or replacing a clogged fuel filter, checking the fuel pump for proper operation, and repairing any wiring issues in the fuel metering control circuit.
7. Is it safe to reset the P0256 code using a scan tool without addressing the underlying issue?
- While clearing the code temporarily may turn off the check engine light, it is not recommended as the underlying problem causing the code will still exist and potentially lead to further issues down the road.
8. How much does it typically cost to repair the P0256 code?
- The cost of repairing the P0256 code can vary depending on the specific cause of the issue, but it may range from a few hundred dollars for minor repairs to over a thousand dollars for more complex issues.
9. Can a DIY enthusiast fix the P0256 code themselves?
- Depending on the root cause of the P0256 code, some DIY enthusiasts with mechanical knowledge and the right tools may be able to address the issue themselves, such as replacing a fuel filter or a faulty fuel injector.
10. How often does the P0256 code occur in vehicles?
- The P0256 code is not as common as some other OBDII codes, but it can still occur in vehicles, particularly in older models or those with high mileage. Regular maintenance can help prevent issues that may trigger this code.
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