The P0628 diagnostic trouble code (DTC) indicates a problem with the fuel pump “A” control circuit, specifically a low voltage condition. This generic powertrain code applies to many OBD-II vehicles from 1996 onwards, including models from Ford, Dodge, Toyota, Chrysler, Jeep, Ram, Chevrolet, Nissan, Mitsubishi, Mercedes, and more. While generic, specific repair steps may vary based on the vehicle’s year, make, model, and powertrain configuration.
What Triggers the P0628 Code?
The P0628 code is triggered when the Powertrain Control Module (PCM) or Engine Control Module (ECM) detects low voltage in the fuel pump “A” control circuit. This can be caused by damaged wiring or connectors within the circuit or issues with the Controller Area Network (CAN) bus. Other modules, like the Alternative Fuel Control Module, Fuel Injection Control Module, or Turbo Control Module, can also trigger this code. The code might appear immediately or after several driving cycles, depending on the vehicle.
The fuel pump is crucial for engine operation, delivering fuel as needed. Its control circuit manages the pump’s on/off cycles based on driver input. A break in this circuit can also activate the P0628 code.
A typical fuel pump with its electrical connector.
Severity and Symptoms of the P0628 Code
The P0628 code signifies a moderately serious issue. While you might still be able to drive, it’s strongly advised against it. Inconsistent fuel delivery and fluctuating fuel mixtures can lead to severe engine damage.
Symptoms of a P0628 code can include:
- Illuminated check engine light
- Engine starting failure
- Engine misfires or stalling
- Engine starting then dying
- Reduced fuel economy
- Engine cranking without starting
- Engine dying after reaching operating temperature
Even without an immediate check engine light, the problem might still exist. Allow for a few driving cycles (e.g., a week) to confirm if the issue is resolved.
Common Causes of the P0628 Code
Several factors can contribute to the P0628 code:
- Malfunctioning fuel pump
- Damaged or severed ground wire in the control module
- Loose ground strap in the control module
- Open, shorted, or corroded wiring in the CAN bus
- Faulty CAN bus
- Loose harnesses and wires causing chafing or a broken circuit
- High resistance in the circuit (e.g., melted or corroded connectors, internal wire corrosion)
Troubleshooting the P0628 Code
1. Consult Technical Service Bulletins (TSBs): Start by checking for TSBs specific to your vehicle’s year, make, and engine. This can save valuable diagnostic time.
2. Scan Modules and Inspect Wiring: Use an OBD-II scanner to assess the electrical health of your vehicle and its modules. Visually inspect connectors and wiring, particularly those under the vehicle near the fuel tank, for damage. Repair or replace any damaged components.
3. Check Ground Circuits: Examine the ground circuits of any component with its own module (like the fuel pump module). Use a separate battery ground or auxiliary ground cable to test. If the problem disappears with the auxiliary ground, the OEM ground cable likely needs repair or replacement. Inspect grounds for corrosion, especially a green ring around the positive battery terminal connector. Clean all contact points if corrosion is present.
4. Trace the Fuel Pump Control Circuit: Using a wiring diagram from your service manual, trace the fuel pump “A” control wire for breaks. Repair by soldering or using butt connectors with heat shrink. Use a multimeter to measure resistance between connectors and pinpoint shorts or opens. A power probe can be helpful for diagnosing faults within the circuit.
Conclusion
Addressing the P0628 code promptly is crucial to prevent potential engine damage. While this guide provides general troubleshooting steps, always prioritize the specific technical data and service bulletins for your vehicle. If you’re unable to resolve the issue, consult a qualified automotive technician for professional diagnosis and repair.
