OBD Spark provides this practical guide to P0231, a generic OBD-II diagnostic trouble code related to a low electrical condition in the fuel pump secondary circuit. This code can be associated with the fuel pump, fuel pump relay, wiring, connectors, power supply, ground circuit or the control strategy used to operate the pump.
P0231 does not automatically mean that the fuel pump itself has failed. Proper diagnosis should determine whether the low condition is caused by the pump, a voltage-drop problem, a relay or fuse issue, damaged wiring, a poor ground, a connector problem, or another part of the fuel-pump control circuit.
P0231 Code Definition
P0231
Fuel / Engine Management
Generic OBD-II Powertrain
Fuel Pump Secondary Circuit Low
How the Fuel Pump Circuit Works
The fuel pump supplies fuel from the tank to the engine fuel system. Depending on the vehicle, the pump may operate at a commanded voltage or may be controlled by a dedicated fuel-pump module.
Battery → Fuse → Fuel Pump Relay / Control Module → Fuel Pump → Ground → Battery
The ECM/PCM may command the fuel pump during engine starting and operation. It can also monitor electrical or feedback information to determine whether the fuel-pump system is operating as expected.
The actual circuit configuration varies significantly between manufacturers and model years.
P0231 Symptoms
- Check Engine Light illuminated
- Engine may crank but fail to start
- Hard starting
- Engine may stall
- Intermittent no-start condition
- Loss of engine power
- Poor acceleration
- Fuel pressure may be low
- Fuel pump may not operate correctly
- Intermittent engine performance problems
Some vehicles may continue to run normally when P0231 is stored, particularly when the electrical fault is intermittent or occurs only under specific operating conditions.
Common Causes of P0231
Internal pump wear or an electrical fault can cause abnormal circuit behavior.
A defective relay can cause voltage loss or an intermittent connection.
Open, damaged, corroded or high-resistance wiring can reduce voltage at the pump.
Loose, corroded or overheated terminals can create excessive resistance.
A poor ground connection can cause a voltage drop and affect pump operation.
A damaged fuse, poor fuse connection or power-supply problem can interrupt pump operation.
Can a Bad Fuel Pump Cause P0231?
Yes. A defective fuel pump can contribute to P0231, but the code should not be used as proof that the pump needs replacement.
A worn pump may draw abnormal current, have an internal electrical problem, or fail to receive the expected voltage because of resistance in the circuit.
Before replacing the pump, check voltage at the pump connector, voltage drop across the power and ground circuits, pump operation and fuel pressure where applicable.
P0231 Diagnosis
A systematic electrical diagnosis is more reliable than replacing the fuel pump immediately after reading the code.
Step 1: Confirm the Code
Connect an OBD2 scanner and check the stored, pending and other related diagnostic trouble codes.
Record freeze-frame data before clearing the codes. Look for additional codes related to fuel pressure, fuel-pump control, power supply or communication.
Step 2: Check the Fuel Pump Operation
Listen for the fuel pump during the ignition-on or starting sequence if the vehicle normally commands the pump at that time.
An absence of pump noise does not by itself prove that the pump has failed. The pump may be controlled differently depending on the vehicle.
Step 3: Inspect the Fuse and Relay
Inspect the fuel-pump fuse and related relay if equipped.
Check for:
- Blown fuse
- Loose fuse terminals
- Burned relay terminals
- Corrosion
- Overheated connectors
- Incorrect replacement fuse
Do not replace a blown fuse repeatedly without determining why it failed.
Step 4: Measure Voltage at the Fuel Pump
Use a digital multimeter to check the voltage supplied to the fuel pump during the operating condition specified by the manufacturer.
The expected voltage and pump-control strategy vary by vehicle. Some systems may use a variable or pulse-width-controlled pump rather than continuously applying battery voltage.
Step 5: Perform a Voltage-Drop Test
A voltage measurement alone may miss a high-resistance connection. A voltage-drop test can help identify resistance in the power or ground side of the circuit while the pump is operating.
Check the voltage drop across:
- Power-side wiring
- Fuel-pump relay contacts
- Connectors
- Ground-side wiring
- Ground connections
Compare the results with manufacturer specifications whenever available.
Step 6: Inspect the Ground Circuit
A poor fuel-pump ground can cause reduced pump voltage and abnormal pump operation.
Inspect the ground connection for corrosion, loose fasteners, damaged wiring or excessive resistance.
Step 7: Check Fuel Pressure
If the engine has starting or performance problems, measure fuel pressure using the correct test equipment and procedure for the vehicle.
Low fuel pressure can result from several conditions, including a weak pump, restricted fuel delivery, inadequate pump voltage, a faulty pressure-control component or other fuel-system problems.
Fuel pressure specifications are vehicle-specific and should not be replaced with a universal value.
P0231 Live Data Diagnosis
An advanced OBD2 scanner may provide useful information about fuel-pump commands and related engine parameters, depending on the vehicle.
Possible parameters may include:
- Fuel pump command
- Fuel pump duty cycle
- Fuel pressure
- Desired fuel pressure
- Actual fuel pressure
- Battery voltage
- Engine RPM
- Engine load
Not every vehicle exposes these PIDs through generic OBD2. Enhanced manufacturer-level diagnostic equipment may provide additional fuel-system information.
Example of P0231 Live Data Diagnosis
Fuel pump commanded ON
Battery voltage appears normal
Fuel-pump voltage is significantly lower than expected
Fuel pressure is below specification
Possible diagnostic direction: Inspect the fuel-pump power circuit, relay/control module, connectors, wiring and ground before replacing the pump.
This example is for diagnostic illustration only. Actual voltage, pressure and control values must be compared with the specifications for the particular vehicle.
P0231 Electrical Testing
Electrical testing is particularly important when the fuel pump itself appears functional but the ECM continues to detect a low circuit condition.
Use a wiring diagram to identify the correct power, ground, control and feedback circuits.
ECM/PCM Command
↓
Fuel Pump Relay / Control Module
↓
Power Supply Circuit
↓
Fuel Pump
↓
Ground Circuit
↓
Battery Ground
The exact circuit can be different from this simplified example. Some vehicles use a separate fuel-pump driver module, variable-speed control or feedback circuit.
P0231 Wiring and Connector Inspection
Inspect the wiring between the fuse, relay or control module and fuel pump.
Look for:
- Broken wires
- Chafed insulation
- Corrosion
- Water intrusion
- Loose terminals
- Spread terminals
- Burned connectors
- Previous repair work
Pay particular attention to the fuel-pump connector because high current through a poor connection can generate heat and increase electrical resistance.
P0231 and Fuel Pump Relay Problems
Vehicles equipped with a conventional fuel-pump relay may develop P0231 when the relay contacts have excessive resistance or fail to provide the expected electrical connection.
A relay can sometimes appear to operate mechanically while still having excessive contact resistance.
Do not diagnose a relay only by listening for a clicking sound. Test the actual circuit voltage and operation according to the manufacturer's wiring diagram.
P0231 and Fuel Pump Control Modules
Many modern vehicles use a dedicated fuel-pump control module instead of a simple relay-based circuit.
The control module may regulate fuel-pump speed and output according to engine demand, fuel pressure and other operating conditions.
A fault in the control module, its power supply, ground, communication circuit or pump output circuit can therefore contribute to fuel-pump-related diagnostic codes.
Always identify the vehicle's actual fuel-pump control architecture before testing individual wires or components.
P0231 vs P0230
Fuel Pump Primary Circuit
Generally relates to a malfunction in the fuel-pump primary control circuit.
Fuel Pump Secondary Circuit Low
Indicates a low electrical condition detected in the fuel-pump secondary circuit.
The exact circuit monitored by the ECM/PCM depends on the vehicle design.
P0231 vs P0232
Fuel Pump Secondary Circuit Low
Fuel Pump Secondary Circuit High
Fuel Pump Secondary Circuit Intermittent
These codes describe different electrical conditions detected by the control system. The exact diagnostic strategy varies by vehicle.
How to Fix P0231
The correct repair depends on the result of the diagnostic tests.
- Repair damaged fuel-pump wiring
- Repair corroded or loose electrical connections
- Repair the fuel-pump ground circuit
- Replace a defective relay when confirmed faulty
- Repair or replace a damaged fuse connection
- Repair or replace a faulty fuel-pump control module when confirmed
- Replace the fuel pump if testing proves the pump is defective
- Repair related power-supply problems
Do not replace the fuel pump simply because P0231 is present. Verify the electrical circuit and fuel-system operation first.
P0231 Repair Cost
The repair cost for P0231 varies significantly depending on the vehicle, the failed component and labor rates in the repair market.
Usually lower cost when the problem is a connector, wire, fuse or ground.
Cost depends on the vehicle's fuel-pump control design.
Can be significantly more expensive because parts and labor vary by vehicle.
Because P0231 can have several electrical causes, obtaining an accurate diagnosis before purchasing parts can prevent unnecessary repair costs.
Is P0231 Serious?
P0231 can be serious. A fuel-pump circuit problem may cause an engine to stall, fail to start or lose power.
If the vehicle stalls unexpectedly, avoid driving it in conditions where loss of engine power could create a safety hazard. Diagnose the fuel and electrical system as soon as practical.
Can You Drive With P0231?
Whether the vehicle can be driven depends on the symptoms and whether the fuel pump is operating correctly.
If the engine starts and runs normally, the fault may be intermittent. However, an intermittent fuel-pump circuit problem can become a no-start or stalling condition without warning.
If the engine is stalling, losing power or experiencing a no-start condition, the vehicle should be diagnosed rather than continued in normal service.
Common Repair Mistakes
1. Replacing the Fuel Pump Immediately
P0231 does not prove that the fuel pump is defective. The power and ground circuits should be tested first.
2. Ignoring Voltage Drop
A multimeter may show acceptable voltage with little or no load while the circuit develops excessive voltage drop when the pump operates.
3. Replacing a Fuse Without Finding the Cause
A repeatedly blown fuse may indicate an electrical overload or short circuit that must be diagnosed.
4. Testing the Wrong Circuit
Modern fuel systems can contain multiple control and feedback circuits. Always use the vehicle-specific wiring diagram.
5. Ignoring the Ground
A poor ground can reduce pump voltage and produce symptoms similar to a defective pump.
6. Using Universal Fuel Pressure Specifications
Fuel pressure requirements vary by vehicle and fuel-system design. Always use the correct specification.
Recommended Diagnostic Tools
- OBD2 scanner with Live Data
- Digital multimeter
- Automotive test light when appropriate
- Fuel pressure gauge compatible with the vehicle
- Vehicle-specific wiring diagram
- Back-probing equipment for electrical testing
- Advanced diagnostic scanner for supported fuel-pump control modules
- Oscilloscope when electrical waveform or control-signal analysis is required
When an Oscilloscope Can Help
An oscilloscope may be useful when a conventional voltage test does not explain an intermittent fuel-pump problem.
Depending on the system, waveform analysis can help evaluate pump current, control signals or other electrical behavior.
Oscilloscope testing should be performed using the correct connection method and manufacturer information because modern fuel-pump control systems can use different control strategies.
P0231 Diagnostic Checklist
☐ Record freeze-frame data
☐ Check for related DTCs
☐ Verify fuel-pump operation
☐ Inspect the fuse
☐ Inspect the fuel-pump relay if equipped
☐ Check power supply
☐ Check fuel-pump voltage
☐ Perform voltage-drop testing
☐ Inspect the ground circuit
☐ Inspect wiring and connectors
☐ Check fuel pressure when required
☐ Test the fuel-pump control module if equipped
☐ Repair the confirmed cause
☐ Clear the code after repairs
☐ Retest the vehicle
Frequently Asked Questions
Does P0231 mean the fuel pump is bad?
No. P0231 can be caused by the fuel pump, wiring, connectors, relay, fuse, ground circuit, control module or another electrical problem.
Can low fuel pressure cause P0231?
Low fuel pressure can occur with a fuel-pump electrical problem, but the code specifically relates to an electrical condition in the monitored fuel-pump circuit. Fuel pressure and the electrical circuit should be tested separately.
Can a bad fuel pump relay cause P0231?
Yes. On vehicles using a conventional fuel-pump relay, excessive resistance or an electrical fault in the relay circuit can contribute to a low secondary-circuit condition.
Can a bad ground cause P0231?
Yes. Excessive resistance in the fuel-pump ground circuit can reduce the voltage available to the pump and affect circuit operation.
How do I fix P0231?
Diagnose the fuel-pump electrical circuit first. Depending on the test results, the repair may involve wiring, connectors, a ground, relay, fuse connection, control module or fuel pump.
Can P0231 cause a no-start?
Yes. If the fuel pump does not receive adequate power or cannot operate correctly, fuel pressure may be insufficient for the engine to start.
Can P0231 cause an engine to stall?
Yes. An intermittent or persistent fuel-pump electrical problem can interrupt fuel delivery and may cause the engine to stall.
Is P0231 a generic OBD2 code?
Yes. P0231 is a generic OBD-II powertrain code, although the actual fuel-pump circuit design and diagnostic procedure vary between manufacturers and vehicles.
Should I replace the fuel pump when I get P0231?
No. Test the electrical supply, ground, voltage drop, control circuit and fuel pressure before replacing the pump.
Final Takeaway
P0231 indicates a low electrical condition in the fuel pump secondary circuit. The fault can involve the fuel pump itself, but it can also originate from the relay, fuse, wiring, connectors, ground circuit, power supply or fuel-pump control module.
The most reliable diagnosis combines an OBD2 scanner with electrical testing and, when necessary, fuel-pressure testing. Checking voltage under load and performing voltage-drop tests can be especially important because a circuit may appear normal during a simple voltage measurement while developing excessive resistance during fuel-pump operation.
Always use the vehicle-specific wiring diagram and manufacturer specifications because fuel-pump control systems vary considerably between vehicles.
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