What Does Error Code P0628 Really Mean?
Error code P0628 is a generic powertrain diagnostic trouble code, according to OBD-II standards. This means it can apply to a wide variety of vehicles manufactured from 1996 onwards, including brands like Ford, Vauxhall, Toyota, Chrysler, Jeep, Ram, Chevrolet, Nissan, Mitsubishi, Mercedes, and many others. While it’s a general code, the specific steps for diagnosis and repair can differ depending on the vehicle’s year, make, model, and engine configuration.
When your vehicle’s diagnostic system flags a P0628 code, it indicates an issue within the control circuit for fuel pump ‘A’. Specifically, the system has detected a low voltage condition in this circuit. This is often triggered by problems like damaged wiring or connectors within the fuel pump control circuit itself, or potentially issues within the Controller Area Network (CAN) bus communication system.
The Powertrain Control Module (PCM) or Engine Control Module (ECM) typically identifies and sets this code. However, other modules in your vehicle can also contribute to flagging P0628, such as:
- Alternative Fuel Control Module
- Fuel Injection Control Module
- Turbo Control Module
Depending on your vehicle’s make and model, the error code might activate after several drive cycles where the fault is detected, or it could appear immediately as soon as the ECM recognises the electrical anomaly.
The fuel pump is a critical component for your vehicle’s operation. Without a functioning fuel pump, the engine cannot receive the necessary fuel to run. The fuel pump control circuit is responsible for regulating the pump’s operation, turning it on and off as needed based on driver demand and engine requirements. It’s important to note that an open circuit within this control system can also trigger the P0628 code, so this possibility should be considered during diagnosis.
A typical fuel pump:
Related fuel pump ‘A’ control circuit codes you might encounter include:
- P0626 Fuel Pump “A” Control Circuit High
- P0627 Fuel Pump “A” Control Circuit Open
How Serious is a P0628 Fault?
This error code represents a moderately serious problem for your vehicle. While you might still be able to drive, it’s strongly advised against doing so unnecessarily. Driving with a P0628 error can lead to inconsistent fuel delivery to the engine. An erratic fuel mixture can potentially cause significant engine damage over time. It’s best to address this issue promptly to prevent further complications.
What Symptoms Might You Notice?
If your vehicle has a P0628 trouble code, you may experience several symptoms, including:
- The “check engine” light or malfunction indicator lamp (MIL) is illuminated on the dashboard.
- Engine fails to start.
- Engine misfires or stalls unexpectedly.
- Engine starts but cuts out shortly after.
- Reduced fuel economy.
- Engine cranks normally but doesn’t start.
- Engine cuts out when it reaches normal operating temperature.
Important Note: Even if the check engine light isn’t immediately on, the problem might still exist. Ensure your vehicle completes a few drive cycles after any repairs to confirm the issue is resolved. A drive cycle typically involves a range of driving conditions over a period of time. If the CEL remains off after a week of normal driving, the problem is likely fixed.
Common Causes Behind the P0628 Code
Several factors can lead to a P0628 error code. These are some of the most common culprits:
- Faulty fuel pump: The fuel pump itself might be failing or malfunctioning internally.
- Ground wire issues: A severed or damaged ground wire within the fuel pump control module circuit.
- Loose ground strap: A detached or loose ground strap in the control module affecting proper grounding.
- Wiring problems: Open, shorted, or corroded wiring within the CAN bus network or the fuel pump control circuit.
- CAN bus malfunction: A fault within the CAN bus system itself.
- Harness/wiring damage: Unsecured wiring harnesses or wires that are chafing or have broken circuits due to rubbing or wear.
- High circuit resistance: Excessive resistance in the circuit, often caused by melted or corroded connectors, or internal wire corrosion.
Troubleshooting Steps for P0628
When diagnosing a P0628 code, start with these troubleshooting steps.
Basic Step 1: Initial Scan and Visual Inspection
Begin by using an OBD-II scanner to read all diagnostic trouble codes stored in your vehicle’s modules. This gives you a comprehensive overview of any electrical or system issues. Crucially, perform a thorough visual inspection of all accessible wiring and connectors related to the fuel pump control circuit. Look for any obvious signs of damage, such as frayed wires, loose connectors, corrosion, or rodent damage. Pay particular attention to connectors and wiring located underneath the vehicle near the fuel tank, as these are exposed to road spray, debris, and harsh weather conditions. Repair or replace any damaged components you find.
Basic Step 2: Ground Circuit Examination
For any component with its own control module, such as the fuel pump module, meticulously check the ground circuits. You can use a separate, known good battery ground to test the ground circuit’s integrity. Connect an auxiliary ground cable to the module’s ground point. If the P0628 code issue resolves with the auxiliary ground connected but returns when using the original equipment manufacturer (OEM) ground, it indicates a problem with the OEM ground cable or connection. In this case, the ground cable requires repair or replacement. Carefully inspect all ground connections for corrosion, loose terminals, or damaged pins, which can create resistance in the circuit. A tell-tale sign of significant corrosion is a green powdery deposit around battery terminals, particularly the positive terminal. If corrosion is present, disconnect the terminal, and thoroughly clean all contact points, the connector face, and the battery post or stud.
Basic Step 3: Circuit Tracing and Resistance Testing
Given that a P0628 code can stem from an open circuit, obtain an electrical wiring diagram for your specific vehicle from a reputable service manual. Use this diagram to identify the fuel pump ‘A’ control circuit. Carefully trace each wire in the circuit, visually inspecting for any breaks or damage along its length. Repair any breaks as needed, ideally by soldering the wires together for a robust and lasting connection. If soldering isn’t possible, use high-quality butt connectors with heat shrink tubing to protect the connection from moisture and the elements.
Employ a multimeter to measure the resistance within the fuel pump control circuit. By systematically testing resistance between different points in the circuit, you can pinpoint the location of a short or open circuit. A power probe tool can be very helpful in this process, allowing you to apply power and ground to specific points in the circuit while measuring voltage drops and current flow, which can aid in locating faults within the entire circuit.
By following these steps, you should be well-equipped to diagnose the cause of the P0628 fuel pump control circuit trouble code. Remember that this information is for general guidance only. Always prioritise consulting the specific technical data and service bulletins for your vehicle model when undertaking any diagnostic or repair work. For more complex issues or if you are not comfortable working on your vehicle’s fuel or electrical systems, it is always recommended to consult a qualified professional mechanic.
Need More Assistance with a P0628 Error?
If you require further help with diagnosing and resolving a P0628 trouble code, consider seeking advice from experienced technicians or utilising online resources specific to your vehicle make and model. Online car repair forums can also be valuable for sharing information and getting insights from other vehicle owners and mechanics.
Disclaimer: This information is provided for informational purposes only. It is not intended as professional repair advice, and we are not liable for any actions taken on your vehicle based on this information. All content on this site is protected by copyright.
