P0231 — Fuel Pump Secondary Circuit Low #

The code description may vary depending on the vehicle manufacturer (OEM). Below are known alternative descriptions for this DTC:

• Fuel Pump Secondary Circuit Low (Ford, GM, Chrysler, Honda, Toyota, Volkswagen, BMW, Mercedes-Benz)
• Fuel Pump Relay Circuit Low (Hyundai, Kia)
• Low Voltage in Fuel Pump Secondary Circuit (Mazda, Nissan, Subaru)

Summary of DTC P0231 #

P0231 is a diagnostic trouble code (DTC) indicating the engine control module (ECM) or powertrain control module (PCM) has detected a low voltage condition in the fuel pump secondary circuit. This secondary circuit refers to the wiring and components that supply power from the fuel pump relay to the fuel pump itself, after the relay has been activated. If the voltage is below a predetermined threshold, the PCM will log this code and may trigger the check engine light. This circuit is critical for proper fuel delivery and, if compromised, can affect engine performance or prevent the engine from starting. While this code rarely points to an immediate catastrophic failure, it should not be ignored, as it can quickly lead to drivability issues.

Common Symptoms for Code P0231 #

A vehicle with a stored P0231 code will often exhibit noticeable symptoms, though the severity can vary based on the specific failure and vehicle design. Typical symptoms include:

• Engine may not start or is hard to start.
• Engine stalls shortly after starting.
• Hesitation or stumbling during acceleration.
• Loss of power, especially under load.
• Check engine light illuminated.
• Low or no fuel pressure detected (if equipped with a gauge or scan tool capability).
• Possible fuel pump relay clicking without pump operation.

Probable Causes for Code P0231 #

The causes of P0231 tend to fall into a few main categories related to the electrical path from the fuel pump relay to the pump itself. Based on frequency and field experience, the most common causes are:

1. Faulty or failing fuel pump (internal electrical failure or excessive resistance)
2. Corroded, damaged, or loose electrical connectors at fuel pump or relay
3. Faulty wiring (open, short to ground, or high resistance) between relay and fuel pump
4. Faulty fuel pump relay (contacts not closing or internal resistance)
5. Blown fuse in the fuel pump circuit
6. PCM/ECM issue (rare, but possible if circuit monitoring fails)
7. Poor ground connection for the fuel pump circuit

Step-by-Step Diagnostic for P0231 #

Diagnosing P0231 requires a logical approach, as the fault can lie anywhere along the secondary fuel pump circuit. Here’s a recommended step-by-step process:

• 1. Verify the code and check for accompanying codes: Use a quality scan tool to confirm P0231 is present and look for other fuel system or powertrain codes.
• 2. Inspect the fuel pump fuse and relay: Check the fuse for continuity and inspect the relay function by swapping it with a known good relay if possible.
• 3. Listen for fuel pump operation: With ignition ON, listen near the gas tank for the fuel pump priming. Absence of sound may confirm a power or pump issue.
• 4. Check for voltage at the fuel pump connector: With the relay energized, use a multimeter to verify that battery voltage is present at the pump connector. Low or no voltage suggests a wiring or relay fault.
• 5. Inspect connectors and wiring: Examine the wiring harness and connectors for corrosion, damage, or looseness. Pay close attention to areas exposed to moisture or road debris.
• 6. Test fuel pump resistance: Disconnect the pump and measure its resistance. Compare to OEM specification. Excessive resistance indicates a failing pump.
• 7. Test circuit continuity: Trace wiring from relay to pump and from pump to ground, checking for open or shorted conditions.
• 8. Check PCM/ECM outputs: If all else checks out, verify the PCM/ECM is correctly grounding the relay and monitoring the circuit as designed.

Possible Repairs for P0231 #

Repairing a P0231 code will depend on which fault is discovered during diagnosis. Here are the repairs most commonly associated with this code:

• Replace a faulty fuel pump if it draws excessive current or fails resistance tests.
• Repair or replace corroded or loose connectors at the fuel pump, relay, or ground points.
• Repair or replace damaged wiring in the secondary circuit between the relay and fuel pump.
• Replace a failed fuel pump relay if it does not energize or pass continuity tests.
• Replace a blown fuse and address the root cause of overcurrent if present.
• Correct poor ground connections by cleaning and tightening ground points.
• Reprogram or replace the PCM/ECM if all wiring, relay, and pump are functional but the module does not monitor or control the circuit correctly (rare).

Can You Drive with Code P0231? #

In most cases, you should not drive with DTC P0231 stored. If the fuel pump circuit is compromised, the engine may stall unexpectedly or fail to start at all, which can leave you stranded or create a dangerous situation on the road. Even if the engine runs, drivability and safety are at risk. It’s best to address this code as soon as possible to avoid getting stuck or causing further damage to the fuel system.

Vehicles Most Commonly Affected by P0231 #

While P0231 can appear on almost any modern vehicle with OBD-II, some makes and models are reported more frequently due to design or component vulnerabilities. Vehicles where this code is seen more often include:

• Ford F-Series (F-150, F-250, F-350, especially 2000s models)
• Chevrolet Silverado and GMC Sierra (mid-2000s)
• Dodge Ram trucks (2002–2012)
• Honda Accord and Civic (late 2000s–early 2010s)
• Toyota Camry, Corolla, Tacoma
• Volkswagen Jetta, Passat
• BMW 3 Series (E90/E92 generation)

Common Mistakes & Best Practices for P0231 #

Misdiagnosis is not uncommon with P0231, as technicians or DIYers may focus on the fuel pump itself before confirming circuit integrity. To avoid wasted time and expense, observe these best practices:

• Always check wiring and connectors before replacing the fuel pump.
• Do not ignore relay and fuse condition—these are quick, inexpensive fixes.
• Use a wiring diagram for your specific model to trace circuits accurately.
• Do not assume the PCM/ECM is faulty unless all other possibilities are exhausted.
• Clear codes and road test after repairs to ensure the issue is resolved.

Express FAQ for DTC P0231 #

Here are quick answers to some common questions about P0231:

• Q: Can a bad fuel pump cause P0231?
  A: Yes, if the pump’s internal electrical components create high resistance or an open circuit, it can trigger this code.
• Q: Is P0231 always caused by a broken fuel pump?
  A: No. Wiring issues, faulty relays, corroded connectors, or blown fuses are just as common. Always diagnose the entire circuit.
• Q: Will clearing the code fix the problem?
  A: No. Clearing the code without repairing the underlying issue will just cause the code to return.
• Q: How urgent is a P0231 code?
  A: It’s urgent—loss of fuel pump operation can lead to no-start or stalling. Diagnose and repair promptly.