P0628 Code: Complete DIY Repair Guide

The P0628 code is a diagnostic trouble code (DTC) that indicates a problem with the fuel pump control circuit. Specifically, it means that the powertrain control module (PCM) has detected a low voltage condition in the fuel pump “A” control circuit. This code can affect various vehicle makes and models, potentially causing drivability issues and reduced fuel efficiency.

Symptoms of P0628 Code

When your vehicle’s PCM detects a P0628 code, you may experience various symptoms that can affect your vehicle’s performance and drivability. Understanding these symptoms can help you identify the issue quickly and take appropriate action. Here are the most common symptoms associated with the P0628 code:

1. Illuminated Check Engine Light: The most obvious sign of a P0628 code is the illumination of the check engine light on your dashboard. This warning light is typically the first indication that something is wrong with your vehicle’s systems.
2. Engine Starting Issues: You may notice that your engine has difficulty starting or fails to start altogether. This is because the fuel pump may not be receiving the proper voltage to operate effectively.
3. Engine Stalling: If the fuel pump isn’t functioning correctly due to low voltage, your engine may stall unexpectedly, especially when idling or during low-speed driving.
4. Reduced Engine Performance: A malfunctioning fuel pump can lead to decreased engine performance, including reduced acceleration and power output.
5. Poor Fuel Economy: When the fuel pump isn’t working efficiently, it can result in improper fuel delivery, leading to decreased fuel economy.
6. Intermittent Power Loss: You might experience sudden power loss while driving, which can be both frustrating and potentially dangerous.
7. Unusual Fuel Pump Noises: In some cases, you may hear unusual noises coming from the fuel tank area, indicating a problem with the fuel pump.
8. Fuel Cap Malfunction Light: Some vehicles may also display a fuel cap malfunction light in addition to the check engine light when a P0628 code is present.

It’s important to note that these symptoms can vary depending on the severity of the issue and the specific make and model of your vehicle. Some vehicles may exhibit all of these symptoms, while others may only show a few. Regardless of the symptoms you’re experiencing, it’s crucial to address the P0628 code promptly to prevent further damage to your vehicle’s fuel system and ensure optimal performance.

Technical Explanation of P0628 Code

To fully understand the P0628 code, it’s essential to delve into the technical aspects of how the fuel pump control circuit operates and why a low voltage condition triggers this specific code.

The fuel pump control circuit is responsible for regulating the power supply to the fuel pump, which is crucial for maintaining proper fuel pressure and delivery to the engine. This circuit typically consists of the following components:

1. Fuel Pump: The device that pressurizes and delivers fuel from the tank to the engine.
2. Fuel Pump Relay: An electrical switch that controls the power supply to the fuel pump.
3. Powertrain Control Module (PCM): The main computer that monitors and controls various engine functions, including the fuel pump circuit.
4. Wiring and Connectors: The electrical pathways that connect all components of the fuel pump control circuit.
5. Fuel Pump Control Module (in some vehicles): A separate module that manages fuel pump operation.

Under normal operating conditions, when you turn the ignition key, the PCM sends a signal to the fuel pump relay, which then closes its internal switch, allowing current to flow to the fuel pump. The fuel pump then pressurizes the fuel system, preparing it for engine operation.

The P0628 code is set when the PCM detects a low voltage condition in this control circuit. Specifically:

1. The PCM expects to see a certain voltage range in the fuel pump control circuit when it’s activated.
2. If the voltage falls below the manufacturer’s specified threshold (typically around 10-12 volts), the PCM interprets this as a “low” condition.
3. This low voltage can occur for various reasons, such as a weak relay, damaged wiring, or a failing fuel pump.
4. When the PCM consistently detects this low voltage condition (the number of detection cycles varies by vehicle make and model), it sets the P0628 code and illuminates the check engine light.

The low voltage condition can manifest in several ways:

• Intermittent low voltage: The circuit may function normally at times but drop below the threshold intermittently.
• Constant low voltage: The circuit consistently operates below the required voltage level.
• No voltage: In severe cases, there may be a complete loss of voltage in the circuit.

It’s important to understand that the P0628 code specifically indicates a problem with the control circuit, not necessarily with the fuel pump itself. While a failing fuel pump can cause low voltage in the circuit, the issue often lies in the electrical components that control the pump rather than the pump itself.

This distinction is crucial for proper diagnosis and repair, as replacing a fuel pump unnecessarily can be an expensive mistake if the real issue is in the wiring, relay, or control module.

Step-by-Step Diagnosis of P0628 Code

Diagnosing the P0628 code requires a systematic approach to identify the root cause of the low voltage condition in the fuel pump control circuit. Follow these steps for a comprehensive diagnosis:

1. Verify the code: – Connect an OBD-II scanner to the vehicle’s diagnostic port. – Retrieve all stored codes and freeze frame data. – Confirm that P0628 is present and note any additional codes.
2. Check Technical Service Bulletins (TSBs): – Research if there are any TSBs related to the P0628 code for your specific vehicle make and model. – TSBs can provide valuable information on known issues and manufacturer-recommended fixes.
3. Inspect the fuel pump relay: – Locate the fuel pump relay (usually in the fuse box). – Check if the relay is seated properly. – Test the relay’s functionality using a multimeter or by swapping it with a known good relay.
4. Examine wiring and connectors: – Visually inspect all wiring and connectors in the fuel pump control circuit. – Look for signs of damage, corrosion, or loose connections. – Pay special attention to ground connections, as they are often a source of electrical issues.
5. Test the fuel pump: – Listen for the fuel pump priming when turning the key to the “ON” position (don’t start the engine). – If no sound is heard, use a fuel pressure gauge to check fuel pressure. – Alternatively, use a multimeter to check for proper voltage at the fuel pump connector when the key is turned on.
6. Check the PCM and fuses: – Inspect all relevant fuses in the fuse box. – Check for any signs of damage or corrosion on the PCM connectors. – If equipped with a separate fuel pump control module, inspect its connections as well.
7. Perform voltage drop tests: – Conduct voltage drop tests across the fuel pump circuit, including the power and ground sides. – This can help identify high resistance points in the circuit that may be causing the low voltage condition.
8. Use advanced diagnostic tools: – If available, use a scan tool with live data capabilities to monitor fuel pump-related parameters. – Look for any abnormal readings or fluctuations in voltage or current.
9. Road test the vehicle: – Clear the codes and perform a road test. – Monitor for any drivability issues and check if the code returns.
10. Analyze results: – Based on the diagnostic steps, determine the most likely cause of the P0628 code. – Proceed with the appropriate repair or further testing as needed.

Remember, diagnosis can be complex, and if you’re unsure at any point, it’s best to consult a professional mechanic or dealership for assistance.

Solution Methods for P0628 Code

Once you’ve diagnosed the root cause of the P0628 code, you can proceed with the appropriate repair. Here are the most common solution methods based on different causes:

1. Faulty Fuel Pump Relay:

• If the relay is defective, replace it with a new one matching your vehicle’s specifications.
• Ensure the new relay is properly seated in the fuse box.
• Clear the code and test drive to confirm the fix.

1. Damaged Wiring or Connectors:

• Repair or replace any damaged wiring in the fuel pump control circuit.
• Clean corroded connectors using electrical contact cleaner.
• If wires are frayed or broken, solder and heat-shrink the connections or replace the entire wiring harness if necessary.
• After repairs, use dielectric grease on connections to prevent future corrosion.

1. Defective Fuel Pump Control Module:

• If your vehicle has a separate fuel pump control module and it’s determined to be faulty, replace it with a new unit.
• Ensure proper coding or programming of the new module if required by the manufacturer.

1. Failed Fuel Pump:

• If the fuel pump itself has failed, it will need to be replaced.
• This typically involves dropping the fuel tank or accessing it through a service panel.
• Always replace the fuel filter when installing a new fuel pump.
• Use only OEM or high-quality aftermarket pumps to ensure proper fit and function.

1. Corroded or Loose Ground Connections:

• Clean all ground connections in the fuel pump circuit using a wire brush or sandpaper.
• Ensure all ground bolts are tight and free of corrosion.
• Apply dielectric grease to prevent future corrosion.

1. PCM Issues:

• If all other components check out and the issue persists, the PCM may need to be reprogrammed or replaced.
• This should be done by a professional as it requires specialized equipment and knowledge.

1. Fuse Replacement:

• If any fuses related to the fuel pump circuit are blown, replace them with fuses of the correct amperage.
• Investigate the cause of the blown fuse to prevent recurrence.

1. Voltage Regulator Repair:

• In some cases, a faulty voltage regulator can cause low voltage in the fuel pump circuit.
• Replace the voltage regulator if it’s determined to be the cause.

After performing any of these repairs:

1. Clear all diagnostic trouble codes (DTCs) using an OBD-II scanner.
2. Start the vehicle and listen for proper fuel pump operation.
3. Perform a road test to ensure the problem is resolved and the code doesn’t return.
4. Monitor the vehicle for several drive cycles to confirm the fix is permanent.

Important: Always disconnect the vehicle’s battery before performing electrical repairs. Follow all safety precautions when working with fuel systems, including proper ventilation and handling of flammable materials.

Cost Estimates for P0628 Code Repairs

The cost of repairing issues related to the P0628 code can vary significantly depending on the root cause of the problem and the make and model of your vehicle. Here’s a breakdown of potential costs for various repairs:

1. Fuel Pump Relay Replacement:

• Parts: $20 – $50
• Labor: $50 – $100
• Total Estimated Cost: $70 – $150

1. Wiring Repair:

• Parts: $10 – $100 (depending on the extent of damage)
• Labor: $100 – $300
• Total Estimated Cost: $110 – $400

1. Fuel Pump Control Module Replacement:

• Parts: $150 – $400
• Labor: $100 – $200
• Total Estimated Cost: $250 – $600

1. Fuel Pump Replacement:

• Parts: $200 – $1000 (varies widely by vehicle)
• Labor: $200 – $500
• Total Estimated Cost: $400 – $1500

1. Ground Connection Repair:

• Parts: $5 – $20
• Labor: $50 – $100
• Total Estimated Cost: $55 – $120

1. PCM Reprogramming:

• Labor: $100 – $200
• Total Estimated Cost: $100 – $200

1. PCM Replacement:

• Parts: $500 – $2000
• Labor: $200 – $500
• Total Estimated Cost: $700 – $2500

1. Fuse Replacement:

• Parts: $5 – $20
• Labor: $50 – $100 (if performed by a mechanic)
• Total Estimated Cost: $55 – $120

1. Voltage Regulator Replacement:

• Parts: $50 – $200
• Labor: $100 – $200
• Total Estimated Cost: $150 – $400

1. Diagnostic Fee:
   • Many shops charge a diagnostic fee of $50 – $150, which may be applied to the cost of repairs if performed at the same shop.

These estimates are general ranges and can vary based on several factors:

• Geographic location (labor rates differ by region)
• Vehicle make and model (some vehicles are more complex or require special tools)
• Parts quality (OEM vs. aftermarket)
• The specific shop or dealership performing the work

Important Notes:

• DIY repairs can significantly reduce labor costs but require proper tools and knowledge.
• Always get multiple quotes from reputable shops before proceeding with expensive repairs.
• Consider the age and value of your vehicle when deciding on extensive repairs.
• Some repairs may be covered under extended warranties or recall notices, so check with your dealership.

Remember, proper diagnosis is crucial to avoid unnecessary parts replacement and ensure cost-effective repairs. If you’re unsure about the diagnosis or repair process, it’s often worth the initial diagnostic fee to have a professional assess the issue accurately.

Warnings and Recommendations for P0628 Code

When dealing with the P0628 code and related fuel system issues, it’s crucial to keep the following warnings and recommendations in mind:

Safety Warnings:

1. Fuel System Pressure: The fuel system remains pressurized even when the engine is off. Always relieve fuel pressure before working on any fuel system components to prevent fuel sprays and potential fires.
2. Flammability: Gasoline is highly flammable. Work in a well-ventilated area, away from open flames or sparks. Have a fire extinguisher rated for fuel fires nearby.
3. Battery Disconnection: Always disconnect the negative battery terminal before working on electrical components to prevent short circuits and potential injury.
4. Proper Lifting: If you need to lift the vehicle to access components, use proper jack stands and follow safe lifting procedures to prevent crushing injuries.
5. Eye Protection: Wear safety glasses to protect your eyes from debris, especially when working under the vehicle.
6. Skin Protection: Use gloves when handling fuel system components to protect your skin from fuel exposure and potential irritation.

General Recommendations:

1. Use OEM Parts: Whenever possible, use Original Equipment Manufacturer (OEM) parts or high-quality aftermarket equivalents to ensure proper fit and function.
2. Follow Manufacturer Procedures: Always consult your vehicle’s service manual for specific procedures and torque specifications.
3. Clean Work Environment: Maintain a clean work area to prevent debris from entering the fuel system during repairs.
4. Document Everything: Keep detailed records of all repairs, including part numbers and any observed issues, for future reference.
5. Address Related Codes: If other diagnostic trouble codes are present along with P0628, address them as well, as they may be related or contributing to the issue.
6. Regular Maintenance: Follow your vehicle’s recommended maintenance schedule to prevent future issues with the fuel