P0628 Fuel Pump "A" Control Circuit Low

The P0628 – Fuel Pump "A" Control Circuit Low diagnostic trouble code (DTC) indicates that the ECM/PCM has detected an abnormally low electrical signal in the control circuit for Fuel Pump "A".

In simple terms:

The engine computer is commanding the fuel pump control system, but the electrical signal in the fuel pump control circuit is lower than expected.

P0628 is primarily an electrical and fuel-pump control problem. It does not automatically mean that the fuel pump itself has failed.

The fault can involve the:

• Fuel pump

• Fuel pump relay

• Fuel Pump Control Module (FPCM)

• Fuel pump driver circuit

• Wiring

• Connectors

• Fuse

• Ground

• ECM/PCM

The exact system differs between vehicle manufacturers.

What Does P0628 Mean?

Modern vehicles do not always power the fuel pump directly from the ECM.

A simplified system can look like this:

ECM/PCM → Fuel Pump Control Circuit → Fuel Pump Control Module/Relay → Fuel Pump → Fuel Rail

The ECM determines how the fuel pump should operate.

If it detects that the control circuit voltage or signal is lower than the expected value, it can store P0628.

The important word is "Control."

P0628 does not necessarily mean that the fuel pressure is low.

It means the electrical control side of the fuel pump system has been detected as low.

What Is Fuel Pump "A"?

"Fuel Pump A" is a generic OBD-II designation.

It does not necessarily mean that the vehicle has two fuel pumps.

Depending on the vehicle, Fuel Pump "A" can refer to:

• The primary fuel pump

• A specific pump circuit

• A fuel pump control module output

• A particular fuel pump relay/control channel

Some vehicles have multiple fuel pumps, while others have only one.

Therefore, the manufacturer's wiring diagram is important when diagnosing P0628.

What Causes P0628?

Common possible causes include:

• Short to ground in the fuel pump control circuit

• Damaged fuel pump wiring

• Corroded connector

• Loose electrical terminal

• Faulty fuel pump relay

• Failed fuel pump control module

• Faulty fuel pump

• Blown or damaged fuse

• Poor fuel pump ground

• Low system voltage

• Damaged ECM/PCM wiring

• Internal ECM/PCM driver failure

A shorted fuel pump or control component can also pull the control circuit voltage down.

Can a Bad Fuel Pump Cause P0628?

Yes.

A failing fuel pump can cause abnormal electrical behavior.

For example, an electrically damaged pump motor may draw excessive current and pull the control circuit voltage down.

However, P0628 should not automatically be interpreted as:

"Replace the fuel pump."

The electrical circuit should be tested first.

Can a Weak Fuel Pump Cause P0628?

Potentially, but not necessarily.

A mechanically worn pump can cause low fuel pressure without producing P0628.

P0628 is specifically associated with the electrical control circuit being low.

Therefore:

Low fuel pressure ≠ automatically P0628

and:

P0628 ≠ automatically low fuel pressure

These are related but different diagnostic issues.

Can a Fuel Pump Relay Cause P0628?

Yes.

A faulty relay can cause an abnormal control signal.

Possible relay problems include:

• Burned contacts

• Internal resistance

• Stuck contacts

• Coil failure

• Corrosion

• Poor socket connection

If the vehicle uses a conventional fuel-pump relay, the relay and its socket should be checked.

Can a Fuel Pump Control Module Cause P0628?

Yes.

Many modern vehicles use a Fuel Pump Control Module (FPCM).

The FPCM can regulate the fuel pump according to engine demand.

If the FPCM has an internal fault or its control circuit is shorted or damaged, P0628 can occur.

A typical arrangement may be:

ECM/PCM → FPCM → Fuel Pump

In such vehicles, replacing the fuel pump without testing the FPCM may not solve the problem.

Can a Fuse Cause P0628?

Yes, depending on the circuit design.

A blown fuse can prevent the fuel pump system from receiving the required power.

However, a simple open circuit may produce a different DTC depending on how the ECM monitors the system.

The fuse should therefore be checked together with the complete circuit.

Can a Bad Ground Cause P0628?

Yes, potentially.

A poor fuel pump ground can cause:

• Low voltage at the pump

• High voltage drop

• Pump malfunction

• Intermittent starting

• Fuel pressure problems

• Abnormal electrical feedback

Check the fuel pump ground under load rather than relying only on a basic continuity test.

Can Low Battery Voltage Cause P0628?

Yes, potentially.

The fuel pump requires sufficient electrical voltage to operate correctly.

If system voltage is abnormally low, the ECM may detect an abnormal control condition.

Check:

• Battery condition

• Battery terminals

• Charging system

• Ground connections

before replacing expensive components.

Can a Bad Alternator Cause P0628?

Potentially.

An alternator that is not charging properly can cause low system voltage.

This can affect fuel pump operation and other electrical systems.

If P0628 appears together with multiple low-voltage or electrical DTCs, check the charging system.

Can a Short to Ground Cause P0628?

Yes.

This is an important possibility.

If the fuel pump control wire is shorted to ground, the control circuit voltage can be pulled down.

For example:

Damaged insulation → Control wire contacts chassis ground → Circuit voltage drops → ECM detects low signal → P0628

Wiring inspection is therefore important.

Can Damaged Wiring Cause P0628?

Yes.

Fuel-pump wiring can be exposed to:

• Heat

• Moisture

• Road debris

• Vibration

• Corrosion

• Previous repair damage

Pay particular attention to wiring near:

• Fuel tank

• Fuel tank connector

• Rear body harness

• Fuel pump module

• Fuse/relay box

Can a Corroded Connector Cause P0628?

Yes.

A corroded connector can increase resistance or create an unstable electrical connection.

Inspect:

• Fuel pump connector

• FPCM connectors

• Relay terminals

• Fuse-box connections

• Ground connections

Look for:

• Green corrosion

• Burned terminals

• Loose pins

• Water intrusion

• Heat damage

Symptoms of P0628

Possible symptoms include:

• Check Engine Light

• Hard starting

• Extended cranking

• Engine stalling

• No-start condition

• Poor acceleration

• Reduced engine performance

• Intermittent fuel pump operation

• Fuel pressure problems

• Engine hesitation

In some vehicles, the engine may run normally for a while before the problem becomes more severe.

Can P0628 Cause a No-Start Condition?

Yes.

If the fuel pump is not receiving the correct electrical command or power, fuel pressure may not build sufficiently for the engine to start.

A typical scenario is:

P0628 → Fuel pump does not operate correctly → Fuel pressure does not build → Engine cranks but does not start

However, the exact behavior depends on the vehicle's fuel system.

Can P0628 Cause Engine Stalling?

Yes.

If the fuel pump intermittently loses electrical control while the engine is running, fuel pressure can drop.

This can cause:

• Hesitation

• Misfire

• Loss of power

• Engine stalling

An intermittent wiring or connector problem can be particularly difficult because the vehicle may restart afterward.

Can P0628 Cause Low Fuel Pressure?

Yes, indirectly.

P0628 itself is an electrical code.

But if the electrical problem prevents the fuel pump from operating correctly, fuel pressure can become too low.

Therefore, a vehicle with P0628 should have both:

Electrical fuel-pump control

and, when symptoms indicate it:

Actual fuel pressure

checked.

Can P0628 Cause Poor Acceleration?

Yes, potentially.

If the pump cannot deliver sufficient fuel under load, the engine may experience:

• Hesitation

• Poor acceleration

• Power loss

• Lean running

• Stalling

This is particularly noticeable during heavy acceleration when fuel demand increases.

Is P0628 a Serious Code?

Yes, it can be.

A fuel-pump control problem can eventually result in:

• No-start

• Engine stalling

• Loss of power

If the vehicle is already stalling or experiencing significant fuel-pressure problems, it should be diagnosed promptly.

Can You Drive With P0628?

If the vehicle starts and operates normally, it may be possible to drive it a short distance for diagnosis.

However, caution is recommended.

If the engine is:

• Stalling

• Losing power

• Difficult to start

• Experiencing severe hesitation

continued driving can leave you stranded or create a safety risk, especially if the engine stalls in traffic.

How Is P0628 Diagnosed?

A systematic electrical diagnosis is recommended.

1. Scan all modules

Check the ECM/PCM, FPCM and other modules for additional DTCs.

Look for related fuel-pump and communication codes.

2. Check the battery

Verify that battery voltage is normal.

3. Check charging voltage

Make sure the alternator is maintaining appropriate system voltage.

4. Check fuel pump fuses

Inspect the correct fuse and verify that power is actually reaching the circuit.

5. Check the fuel pump relay

If equipped, test the relay and its socket.

6. Check fuel pump power and ground

Measure voltage at the fuel pump while the pump is commanded on.

7. Perform voltage-drop testing

Check both the positive and ground sides under load.

8. Inspect wiring

Look for shorts, open circuits, damaged insulation and corrosion.

9. Check the FPCM

If the vehicle uses a Fuel Pump Control Module, check its power, ground, communication and output.

10. Measure fuel pressure

If symptoms indicate a fuel-delivery problem, verify actual fuel pressure against the manufacturer's specification.

11. Check ECM/PCM control

Only after the external circuit has been verified should the ECM/PCM driver circuit become a primary suspect.

Why Is Voltage-Drop Testing Important?

A circuit can show battery voltage with a multimeter but still fail under load.

For example:

12.4 V with no load → appears normal

but:

Voltage drops significantly when fuel pump operates → excessive resistance

Possible sources include:

• Corroded connector

• Weak ground

• Damaged wiring

• Poor relay contact

Voltage-drop testing can reveal problems that a simple voltage measurement may miss.

How Do You Test the Fuel Pump?

The exact procedure depends on the vehicle.

Generally, the technician should determine:

• Commanded fuel-pump state

• Voltage supplied to the pump

• Ground quality

• Pump current draw

• Fuel pressure

An unusually high current draw can suggest a mechanically or electrically failing pump.

An unusually low or zero current draw can indicate an open circuit, disconnected pump or failed pump.

Can Fuel Pump Current Draw Help Diagnose P0628?

Yes.

Current measurement can be useful.

For example:

Excessive current → Possible internally failing or mechanically restricted pump

No current → Open circuit, disconnected pump or failed motor

Abnormal current + low control voltage → Possible circuit or pump fault

The manufacturer's specifications should be used because normal current varies significantly between fuel-pump designs.

What If P0628 Appears With P0627?

These codes are closely related.

P0627 – Fuel Pump "A" Control Circuit/Open

generally indicates an open or interrupted fuel-pump control circuit.

P0628 – Fuel Pump "A" Control Circuit Low

indicates that the monitored control circuit is lower than expected.

Both can involve the same fuel-pump control system but point toward different electrical conditions.

What If P0628 Appears With P0629?

P0628 – Fuel Pump "A" Control Circuit Low

P0629 – Fuel Pump "A" Control Circuit High

These codes represent opposite electrical conditions in the monitored control circuit.

If P0628 and P0629 appear intermittently, investigate unstable wiring, connectors, control-module operation and power supply.

What If P0628 Appears With P069E?

P069E – Fuel Pump Control Module Requested MIL Illumination

can appear when the FPCM detects a problem and requests that the ECM illuminate the MIL.

If P0628 and P069E are present together, the Fuel Pump Control Module and its communication/control circuit deserve particular attention.

What If P0628 Appears With U-Codes?

If P0628 occurs together with several communication codes, do not immediately replace the fuel pump.

Investigate:

• FPCM communication

• CAN wiring

• Module power

• Module ground

• Network voltage

A communication or power problem can affect fuel-pump control.

Can P0628 Be Caused by the ECM/PCM?

Yes, but this should generally be considered after the external circuit has been tested.

The ECM/PCM may contain the driver circuitry that controls the fuel pump relay or communicates with the FPCM.

If the driver circuit fails internally, the ECM may not produce the correct control signal.

Before condemning the ECM, verify:

Power → Ground → Wiring → Relay/FPCM → Fuel pump → Control signal

Can P0628 Be Fixed Without Replacing the Fuel Pump?

Yes.

Possible repairs include:

• Repairing damaged wiring

• Cleaning or replacing connectors

• Repairing a ground

• Replacing a fuse

• Replacing a faulty relay

• Repairing/replacing the FPCM

• Correcting battery or charging problems

• Repairing the ECM control circuit

The fuel pump should only be replaced when testing confirms that it is faulty.

Can P0628 Be Cleared With an OBD Scanner?

The DTC can usually be cleared with a compatible diagnostic scanner.

However, clearing the code does not repair the underlying electrical problem.

If the control circuit remains low, P0628 will return.

The correct sequence is:

Diagnose → Repair → Clear → Test → Rescan

Does P0628 Mean the Fuel Pump Is Bad?

No.

This is one of the most important points.

P0628 identifies a low condition in the Fuel Pump "A" control circuit.

The problem may be:

Fuel pump

but it may also be:

Relay → FPCM → Wiring → Connector → Ground → Fuse → ECM/PCM

Replacing the pump without testing the circuit can result in unnecessary expense.

Common Diagnostic Mistakes

Replacing the fuel pump immediately

The fault may be in the control circuit.

Checking only fuel pressure

P0628 is primarily an electrical fault, so the control circuit must also be tested.

Checking voltage without load

A circuit can show normal voltage with no load but suffer a large voltage drop when the pump operates.

Ignoring the fuel-pump ground

A poor ground can create low-voltage conditions.

Ignoring the FPCM

Vehicles equipped with a Fuel Pump Control Module require that module to be included in the diagnosis.

Ignoring additional U-codes

Communication problems can affect fuel-pump control.

How Is P0628 Repaired?

The correct repair depends on the confirmed cause.

Possible repairs include:

• Repairing damaged fuel-pump wiring

• Repairing a short to ground

• Repairing an open circuit

• Replacing a faulty relay

• Replacing a damaged fuse

• Cleaning or replacing corroded connectors

• Repairing the fuel pump ground

• Replacing a defective FPCM

• Replacing a faulty fuel pump

• Repairing an ECM/PCM driver circuit

• Correcting battery or charging-system problems

How Do You Clear P0628?

After repairing the problem:

Scan all modules → Check battery voltage → Test fuel-pump circuit → Verify power and ground → Test relay/FPCM → Test pump → Verify fuel pressure if necessary → Repair fault → Clear DTC → Start engine → Road test → Rescan

If P0628 does not return, the repair is likely successful.

Final Thoughts on P0628

P0628 – Fuel Pump "A" Control Circuit Low indicates that the vehicle's control system has detected an abnormally low electrical condition in the Fuel Pump "A" control circuit.

The most important areas to investigate are:

Fuel pump → Fuel pump relay → FPCM → Wiring → Connectors → Ground → Fuse → Battery voltage → ECM/PCM control circuit

The most important point is that P0628 does not automatically mean the fuel pump needs to be replaced.

A proper diagnosis should first determine whether the low condition is being caused by the pump itself, excessive resistance, a short to ground, a faulty relay, a Fuel Pump Control Module problem, damaged wiring, poor grounding or an ECM/PCM control fault.

If the vehicle is experiencing hard starting, stalling or loss of power, the problem should be addressed promptly because a fuel-pump control failure can eventually leave the vehicle unable to start.