Technical Description of OBD-II Trouble Code
The control circuit for Fuel Pump A is experiencing low voltage.
What does that mean?
This is a generic diagnostic trouble code (DTC) for the powertrain and is applicable to many OBD-II vehicles manufactured from 1996 onwards. This includes vehicles from various manufacturers such as Ford, Dodge, Toyota, Chrysler, Jeep, Ram, Chevrolet, Nissan, Mitsubishi, Mercedes, and others. While the code is generic, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
If the P0628 code appears, it indicates a problem in the control circuit for fuel pump “A”. Specifically, it means that a low voltage situation has been detected. This is typically caused by damaged wires or connectors within the circuit or issues with the Controller Area Network (CAN) bus. The Powertrain Control Module (PCM) or the Engine Control Module (ECM) usually identifies this code, but other supporting modules can also trigger it, such as:
Depending on the vehicle’s make and model, it may take several drive cycles for the code to activate, or it may be an immediate response as soon as the ECM detects the fault.
The fuel pump plays a crucial role in the overall drivability of the vehicle as it delivers fuel to the engine. The control circuit is responsible for turning the pump on and off based on the operator’s requirements. An open circuit within this circuit can also trigger the P0628 code, so it’s important to consider this before proceeding with any diagnosis.
A typical fuel pump:
Other related codes for the control circuit of fuel pump A include:
What is the severity of this DTC?
This particular trouble code is moderately severe for your vehicle. You can still use your vehicle despite the problem, but it is highly recommended to avoid doing so. Intermittent fuel delivery to the engine and erratic or fluctuating fuel mixture can potentially cause severe engine damage.
What are some of the symptoms of the code?
Symptoms of a P0628 trouble code may include:
Note: Even if the check engine light does not immediately illuminate, the problem may still be unresolved. Always ensure that your vehicle has gone through a few drive cycles. For example, drive the car for a week. If the check engine light is not illuminated by the end, the issue is most likely resolved.
What are some of the common causes of the code?
Causes for this code may include:
What are some P0628 troubleshooting steps?
The first thing I recommend is to research the Technical Service Bulletins (TSB’s) for your specific vehicle based on the year, model, and power plant. In some cases, this can save a lot of time by providing guidance in the right direction.
Basic Step 1
Always scan and test each module using an OBD-II scanner to assess the overall electrical condition of your vehicle and its modules. Also, visually inspect the connectors and wiring for any obvious damage, and repair or replace as necessary. Pay close attention to the health of these components, as they are often located under the vehicle near the fuel tank and can be susceptible to road debris and the elements.
Basic Step 2
When dealing with a component that has its own module (e.g. fuel pump module), examine the ground circuits. You can do this by using a separate battery ground, such as an auxiliary ground cable. If the problem is resolved with the auxiliary ground attached but returns when the OEM ground is used, it indicates that the ground cable is causing the issue and needs to be repaired or replaced. Thoroughly inspect the grounds for corroded connections, terminals, pins, etc. that could be causing resistance in the circuit. Excessive corrosion is often indicated by a green ring around the connector attached to the positive battery terminal. If present, remove the terminal and clean all contact points, the connector face, and the terminal post/stud.
Basic Step 3
Since the cause of the P0628 code could be an open circuit, identify the circuit using an electrical wiring diagram from your service manual. Once identified, trace the individual fuel pump A control wire to check for any obvious breaks. Repair as necessary by soldering the wire or using butt connectors with heat shrink for insulation. Use a multimeter to measure the resistance between connectors in the circuit to pinpoint the location of the short or open. A power probe style tool is highly recommended if there is a fault somewhere within the entire circuit.
I hope this article has provided helpful guidance for diagnosing the problem with your fuel pump control circuit trouble code. Please note that this article is strictly informational, and the specific technical data and service bulletins for your vehicle should always take priority.
