22-06-2022
13 min.
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P0629 Fuel Pump "A" Control Circuit High

The P0629 trouble code is a generic OBD-II diagnostic trouble code related to the Fuel Pump "A" control circuit.

P0629 – Fuel Pump "A" Control Circuit High

This code means that the ECM/PCM has detected a higher-than-expected voltage or electrical signal in the control circuit for Fuel Pump "A".

The code does not automatically mean that the fuel pump itself has failed. The problem may be related to the fuel pump relay, fuel pump control module, wiring, connectors, power supply, ground circuit, or the ECM/PCM.

Depending on the vehicle, Fuel Pump "A" may refer to the primary fuel pump or to a particular fuel-pump control circuit defined by the manufacturer.

What Does P0629 Mean?

P0629 can be understood as:

P = Powertrain
0 = Generic OBD-II code
6 = Computer output/control-related fault
2 = Fuel and air metering control
9 = Circuit high

In simple terms:

The engine control module has detected an excessively high electrical signal in the control circuit for Fuel Pump "A".

The exact voltage threshold and circuit design vary between vehicles.

What Is Fuel Pump "A"?

The fuel pump delivers fuel from the fuel tank toward the engine.

Depending on the vehicle, the fuel system may include:

An electric fuel pump
Fuel pump relay
Fuel pump control module
Fuel pressure sensor
Fuel pressure regulator
High-pressure fuel pump
Low-pressure fuel pump

The term "A" is manufacturer-specific.

On some vehicles, it identifies the primary fuel pump circuit. On vehicles with multiple pumps or more sophisticated fuel systems, it may distinguish one pump or control circuit from another.

Therefore, the vehicle's wiring diagram should be used to determine exactly what Fuel Pump "A" refers to.

What Does "Circuit High" Mean?

The word High means that the control module is detecting a voltage or control signal that is higher than the expected range.

This can happen because of:

Short to battery voltage
Incorrect wiring
Faulty fuel pump control module
Faulty relay
Damaged wiring
Electrical backfeed
Faulty fuel pump
Control-module problem

It does not necessarily mean that fuel pressure itself is too high.

This distinction is important.

P0629 is an electrical control-circuit code, not a direct fuel-pressure code.

Symptoms of P0629

Possible symptoms include:

Check Engine Light
Engine cranks but does not start
Difficult starting
Long cranking time
Engine stalling
Intermittent starting problems
Poor acceleration
Engine hesitation
Reduced engine power
Fuel pump running continuously
Abnormal fuel pump noise
Fuel system warning messages
Limp mode on some vehicles

The severity depends on how the fuel pump is controlled and whether the pump can still operate correctly.

Can P0629 Prevent the Engine From Starting?

Yes.

If the fuel pump is not being controlled correctly, the engine may not receive sufficient fuel pressure for starting.

Possible results include:

Crank-no-start
Extended cranking
Intermittent starting
Starting and immediately stalling

However, if the fuel pump continues to operate despite the control-circuit fault, the vehicle may still start and run.

Can P0629 Cause Engine Stalling?

Yes.

If the fuel pump loses proper control while the engine is running, fuel pressure may become unstable or fuel delivery may stop.

This can cause the engine to:

Hesitate
Lose power
Stall
Restart after cooling down or cycling the ignition

Is P0629 Serious?

Yes, potentially.

Fuel delivery is essential for engine operation.

If the fuel pump control circuit has an electrical fault, the vehicle can experience sudden loss of fuel pressure and engine power.

If the engine stalls unexpectedly, the vehicle should not be driven until the problem is diagnosed.

Common Causes of P0629

Short to battery voltage

A control wire may be contacting a constant or switched power supply.

Faulty fuel pump relay

A relay that is stuck or internally damaged can cause abnormal voltage in the control circuit.

Faulty fuel pump control module

Many modern vehicles use an electronic fuel pump driver or fuel pump control module.

A failure inside this module can cause a control-circuit-high condition.

Damaged wiring

The wiring may be:

Chafed
Melted
Pinched
Incorrectly repaired
Shorted to another circuit

Corroded connector

Water or corrosion can alter the electrical characteristics of the control circuit.

Faulty fuel pump

An internally damaged fuel pump can affect the electrical behavior of the circuit.

Incorrect aftermarket wiring

Alarm systems, remote starters or other modifications can interfere with fuel-pump wiring.

Faulty ECM/PCM

A control-module problem is possible but is generally less common than wiring, relay or pump-control faults.

Can a Bad Fuel Pump Cause P0629?

Yes, it can.

An internally failing fuel pump may create abnormal electrical behavior.

However, P0629 specifically indicates a high control-circuit condition, so the pump should not automatically be blamed.

The control circuit, relay, module, wiring and actual pump operation should all be tested.

Can a Bad Fuel Pump Relay Cause P0629?

Yes.

A relay that is:

Stuck closed
Internally shorted
Incorrectly wired
Electrically damaged

can cause an abnormal control signal.

If the fuel pump continues running when it should be switched off, the relay should be investigated.

Can a Fuel Pump Control Module Cause P0629?

Yes.

Modern vehicles may use a dedicated fuel pump control module to regulate pump voltage or current.

Depending on the design, this module may:

Turn the pump on and off
Control pump speed
Adjust pump output
Monitor pump current
Communicate with the ECM/PCM

A failure in this module can result in P0629.

Can Wiring Cause P0629?

Yes.

Wiring should be inspected carefully.

Look for:

Short to battery positive
Short to ignition voltage
Melted insulation
Chafing
Pinched wires
Corroded wires
Incorrect previous repairs
Damaged terminals

Fuel-pump wiring is often routed underneath the vehicle or around the fuel tank, where it can be exposed to moisture, road debris and corrosion.

Can a Bad Ground Cause P0629?

A poor ground can affect fuel pump operation, although it more commonly causes low voltage or inadequate pump performance.

The ground circuit should still be checked because a poor ground can create abnormal voltage measurements and cause the control system to behave incorrectly.

Can a Fuse Cause P0629?

A fuse problem more commonly causes a loss of power rather than a circuit-high condition.

However, the relevant fuel-pump fuse should still be checked.

Also inspect the fuse box for:

Heat damage
Corrosion
Loose terminals
Water intrusion

Can P0629 Be Caused by an Overcharging Alternator?

Potentially.

If the entire vehicle electrical system is experiencing excessive voltage, fuel-pump control electronics may be affected.

If P0629 appears together with several other circuit-high or voltage-high codes, check:

Battery voltage
Alternator output
Voltage regulator
Charging-system stability

before replacing the fuel pump.

Can P0629 Cause High Fuel Pressure?

Not necessarily.

The word High in P0629 refers to the electrical circuit, not directly to fuel pressure.

A high electrical control signal could potentially cause abnormal pump operation on certain systems, but P0629 should not be interpreted as "fuel pressure too high."

Actual fuel pressure should be measured separately when necessary.

Can P0629 Cause Low Fuel Pressure?

It can indirectly.

If the fuel pump is not being controlled correctly, it may not operate at the correct speed.

This can result in inadequate fuel delivery and low fuel pressure.

Possible symptoms include:

Poor acceleration
Hesitation
Hard starting
Stalling
Lack of power

Actual fuel pressure should be measured to confirm this condition.

Can P0629 Cause Poor Acceleration?

Yes.

If the fuel pump is not receiving or responding to the correct control signal, fuel delivery may not meet engine demand.

The problem can become more noticeable during:

Hard acceleration
High engine RPM
Heavy loads
Uphill driving

Can P0629 Cause Limp Mode?

Yes, depending on the vehicle.

If the ECM/PCM determines that fuel delivery cannot be reliably controlled, it may activate a protective strategy.

The vehicle may experience:

Reduced engine power
Limited RPM
Restricted acceleration

How to Diagnose P0629

A systematic electrical and fuel-system diagnosis is recommended.

1. Scan all diagnostic codes

Do not diagnose P0629 in isolation.

Look for additional codes involving:

Fuel pressure
Fuel pump
Fuel pump control module
Fuel pressure sensor
Fuel system
Battery voltage
Communication

Additional codes can help identify the source.

2. Determine what Fuel Pump "A" means

Use the manufacturer's wiring diagram and service information.

Identify:

Fuel Pump "A"
Control module
Relay
Fuse
Power supply
Ground
ECM/PCM control wire

3. Check battery voltage

Verify that the vehicle's electrical system is operating within specification.

4. Check charging voltage

An overcharging alternator can cause electrical circuit-high codes.

5. Check the fuel-pump fuse

Inspect the fuse and its terminals.

If a fuse is repeatedly blowing, investigate the underlying short circuit.

6. Check the fuel pump relay

Test the relay's:

Power supply
Ground, if applicable
Control signal
Switching operation

7. Inspect the wiring

Look for:

Short to power
Damaged insulation
Corrosion
Broken wires
Incorrect repairs

8. Check the connectors

Inspect the fuel pump and control-module connectors for:

Corrosion
Water
Loose pins
Bent terminals
Poor terminal tension

9. Measure the control circuit voltage

Measure the voltage on the Fuel Pump "A" control circuit and compare it with the manufacturer's specification.

Do not assume that the control circuit should always have 12 volts.

Some modern fuel pump systems use PWM or other electronic control strategies.

10. Test the fuel pump control module

If equipped, verify its:

Power
Ground
Communication
Input signals
Output signal

11. Test the fuel pump

Check:

Pump operation
Current draw
Supply voltage
Ground
Fuel pressure

An abnormal current draw can indicate a failing pump.

12. Measure fuel pressure

If the vehicle has starting or performance problems, verify actual fuel pressure.

Compare it with the manufacturer's specifications.

13. Check the ECM/PCM control circuit

If the external circuit and fuel pump system are functioning correctly, investigate the ECM/PCM control output.

How to Test the Fuel Pump

A proper fuel-pump diagnosis may include:

Listening for pump operation during key-on
Measuring pump voltage
Measuring pump ground voltage drop
Measuring pump current draw
Measuring fuel pressure
Testing commanded pump speed
Checking the control signal

The exact procedure depends on whether the vehicle uses a conventional relay-controlled pump or an electronically controlled variable-speed pump.

Why Current Draw Matters

A fuel pump can sometimes receive apparently correct voltage but still operate incorrectly.

Measuring current draw can reveal:

Worn pump motor
Mechanical pump resistance
Electrical short
Excessive load
Internal pump failure

An abnormal current reading can help distinguish a pump problem from a wiring problem.

Can P0629 Be Intermittent?

Yes.

Intermittent P0629 can be caused by:

Loose connectors
Corrosion
Wiring movement
Heat
Vibration
Relay problems
Intermittent shorts
Fuel pump control-module problems

The vehicle may start and drive normally and then suddenly develop a starting or stalling problem.

Why Does P0629 Appear When the Vehicle Is Hot?

Heat can affect:

Fuel pump motors
Relays
Control modules
Wiring
Electrical connectors

A worn fuel pump can also become more problematic as its internal components heat up.

If the fault occurs only after extended driving, test the fuel pump and control circuit under the same conditions.

Can P0629 Return After Clearing the Code?

Yes.

If the electrical fault remains, the ECM/PCM will detect it again.

Clearing the code does not repair the fuel-pump circuit.

Can You Drive With P0629?

It is not recommended to ignore P0629.

If the vehicle is experiencing:

Engine stalling
Hard starting
Sudden loss of power
Fuel-pressure problems
Intermittent fuel-pump operation

the vehicle should be diagnosed before continued driving.

An engine that suddenly loses fuel delivery can stall unexpectedly.

Does P0629 Damage the Engine?

P0629 itself does not normally cause immediate mechanical engine damage.

However, incorrect fuel delivery can cause poor engine operation.

Depending on the actual fault, prolonged driving can result in:

Poor combustion
Lean operation
Reduced performance
Increased emissions
Engine stalling

The underlying electrical problem should therefore be corrected.

Common Diagnostic Mistakes With P0629

Immediately replacing the fuel pump

P0629 is a control-circuit code. The relay, control module and wiring may be responsible.

Assuming "High" means high fuel pressure

It does not. "High" refers to the electrical control circuit.

Ignoring the fuel pump control module

Many modern vehicles use electronically controlled fuel pumps.

Ignoring the charging system

Abnormally high vehicle voltage can affect electronic fuel-pump controls.

Ignoring wiring near the fuel tank

This area is exposed to moisture and physical damage.

Measuring only fuel pressure

A correct or incorrect fuel pressure reading does not by itself identify an electrical control-circuit fault.

Replacing the ECM too quickly

The external circuit should be thoroughly tested first.

What Is the Correct Repair for P0629?

The appropriate repair depends on the confirmed cause.

Possible repairs include:

Repairing a short to power
Repairing damaged wiring
Replacing damaged connectors
Replacing a faulty fuel pump relay
Replacing a faulty fuel pump control module
Repairing a poor ground
Replacing a defective fuel pump
Repairing charging-system problems
Correcting aftermarket wiring
Repairing ECM/PCM control wiring
Updating control-module software where applicable
Replacing the ECM/PCM only after confirming an internal fault

How to Verify the Repair

After completing the repair:

Clear the diagnostic codes.
Check battery and charging voltage.
Verify the Fuel Pump "A" control signal.
Confirm fuel pump operation.
Measure fuel pressure.
Check fuel pump current draw where appropriate.
Start the engine.
Test the vehicle under different loads.
Perform another diagnostic scan.

P0629 should not return, and fuel pressure and pump operation should remain within specification.

Frequently Asked Questions About P0629

What does P0629 mean?

P0629 means the ECM/PCM has detected higher-than-expected voltage in the Fuel Pump "A" control circuit.

Does P0629 mean the fuel pump is bad?

No. The problem may be the wiring, relay, fuel pump control module, electrical supply, connector or ECM/PCM.

Does "high" mean high fuel pressure?

No. It refers to high electrical voltage in the control circuit.

Can P0629 prevent the car from starting?

Yes. If fuel pump operation is affected, the engine may crank without starting.

Can P0629 cause stalling?

Yes. An intermittent or complete loss of fuel-pump control can cause the engine to stall.

Can a bad fuel pump relay cause P0629?

Yes.

Can a fuel pump control module cause P0629?

Yes.

Can wiring cause P0629?

Yes. A short to battery voltage or another power circuit is a possible cause.

Can an alternator cause P0629?

An overcharging electrical system can potentially contribute to high-voltage faults.

Can P0629 cause low fuel pressure?

Yes, indirectly, if incorrect pump control results in inadequate fuel delivery.

Can P0629 cause high fuel pressure?

It can potentially affect pump operation, but the code itself specifically describes an electrical circuit-high condition, not a fuel-pressure-high condition.

Can P0629 be intermittent?

Yes.

Can I drive with P0629?

If the vehicle has stalling, hard starting or sudden power loss, continued driving is not advisable.

Should I replace the fuel pump?

Not automatically. Test the control circuit, relay, module, wiring, pump voltage and fuel pressure first.

Should I replace the ECM?

No. An ECM fault should only be considered after the fuel-pump circuit and related components have been properly tested.

Final Thoughts on P0629

P0629 – Fuel Pump "A" Control Circuit High indicates that the ECM/PCM has detected a higher-than-expected electrical signal in the control circuit for Fuel Pump "A".

The most important areas to investigate are:

Fuel pump
Fuel pump relay
Fuel pump control module
Wiring
Connectors
Fuses
Grounds
Battery voltage
Charging system
Fuel pressure
Fuel pump current draw
ECM/PCM control circuit

A logical diagnostic sequence is:

Scan All Codes → Identify Fuel Pump "A" Circuit → Check Battery/Charging Voltage → Inspect Fuse and Relay → Check Wiring and Connectors → Measure Control Voltage → Test Fuel Pump Module → Test Pump Current and Voltage → Measure Fuel Pressure → Evaluate ECM/PCM

The most important point is that P0629 is an electrical control-circuit fault, not simply a "bad fuel pump" code. The word High refers to the electrical signal, not necessarily fuel pressure. Testing the complete fuel-pump control circuit before replacing the pump can prevent unnecessary repairs.