P0231 Fuel Pump Secondary Circuit Low: What It Means and How to Fix It

The bottom line: The P0231 code means your vehicle’s powertrain control module (PCM) has detected a low voltage condition in the fuel pump’s secondary (feedback) circuit. This is a serious issue that can prevent your car from starting or cause it to stall while driving. The most common causes are a faulty fuel pump relay, a damaged fuel pump, or wiring problems. You should not drive the vehicle with this code active, as it can lead to a complete loss of engine power and potential safety hazards .

What Is the P0231 Code?

The P0231 diagnostic trouble code (DTC) is formally defined as “Fuel Pump Secondary Circuit Low.” It is a generic powertrain code that applies to all vehicles equipped with OBD-II, including cars from Ford, Chevrolet, Honda, Toyota, and many others .

In simple terms, your vehicle’s fuel pump has two circuits: a primary circuit that supplies power to the pump, and a secondary (feedback) circuit that tells the PCM how the pump is performing. When the PCM detects that the voltage on this secondary circuit is lower than the specified range, it triggers the P0231 code .

Symptoms of P0231

If your vehicle has this code, you will likely experience one or more of the following symptoms :

  1. Engine Cranks But Won’t Start – This is the most common symptom. The starter turns the engine over, but the fuel pump isn’t delivering enough fuel pressure.
  2. Engine Stalls While Driving – The vehicle may suddenly lose power and shut off, especially under load or when accelerating.
  3. Long Cranking Time – You may need to crank the engine for several seconds before it fires up.
  4. Check Engine Light Is On – The MIL (malfunction indicator lamp) will illuminate on your dashboard.
  5. Poor Engine Performance – If the vehicle does run, you may notice hesitation, rough idling, or a lack of power.

What Causes the P0231 Code?

There are several common causes for this code. The most frequent ones are listed below :

  1. Faulty Fuel Pump Relay – The relay controls power to the fuel pump. A failed relay will cause low voltage to the pump.
  2. Damaged Fuel Pump – The internal motor or brushes may be worn out, causing it to draw too much current or not enough.
  3. Wiring or Connector Issues – Corroded, broken, or loose wires in the fuel pump harness can cause voltage drops.
  4. Blown Fuse – A blown fuel pump fuse or a fusible link will cut power to the circuit.
  5. Bad Ground Connection – Poor ground connections at the fuel pump or PCM can cause low voltage readings.
  6. Failed PCM – In rare cases, the PCM itself may be defective.

How Serious Is the P0231 Code?

This code is serious. Multiple sources strongly advise against driving the vehicle with an active P0231 code . The fuel pump is responsible for delivering fuel from the tank to the engine at the correct pressure. If the secondary circuit voltage is low, the pump may not be operating at full capacity or may fail completely at any moment.

If the pump stops while you are driving, you will lose all engine power, which means you will also lose power steering and power brake assist. This can create a dangerous situation, especially in traffic or on the highway.

How to Diagnose the P0231 Code

Diagnosing a P0231 code requires a systematic approach. Here are the steps a professional mechanic would follow, and what you can do yourself if you have basic tools and a multimeter :

  1. Check the Fuel Pump Fuse and Relay – Start with the simplest checks. Locate the fuel pump fuse in your vehicle’s fuse box (usually under the dashboard or under the hood). Inspect it for a broken wire. Then, swap the fuel pump relay with a known good relay of the same type.
  2. Inspect the Wiring and Connectors – Visually examine the wiring harness from the fuel pump to the PCM. Look for cuts, frayed wires, corrosion, or loose connections. Pay special attention to the connector at the fuel pump itself.
  3. Test Voltage at the Fuel Pump – Using a digital multimeter, check the voltage at the fuel pump connector. With the ignition on, you should see battery voltage (around 12.6 volts) on the power wire. If the voltage is low, the problem is upstream.
  4. Check the Ground Circuit – Test the ground wire from the fuel pump to the chassis. A poor ground can cause low voltage readings.
  5. Test the Fuel Pump Relay Circuit – With the relay removed, check for voltage and ground signals at the relay socket.

Repair Options and Estimated Costs

The cost to fix a P0231 code depends entirely on the root cause. Here are the typical repair scenarios :

  1. Replace Fuel Pump Relay or Fuse – $10 to $50. This is the cheapest fix, but it is also the least common root cause.
  2. Repair Wiring or Connector – $100 to $300. If the issue is a corroded connector or a broken wire, a repair may be straightforward.
  3. Replace the Fuel Pump – $400 to $1,200. This is the most common repair. The fuel pump is located inside the fuel tank, so labor costs are high because the tank must be lowered or removed.
  4. Replace the Fuel Pump Module – $500 to $1,500. Many modern vehicles use a module that includes the pump, sending unit, and filter.

KEMSO Fuel Pump: The Best Replacement for Your Vehicle

When it comes time to replace your fuel pump, you need a part that is reliable, performs like the original, and comes with a solid warranty. KEMSO Fuel Pumps are the #1 aftermarket choice for American drivers.

Why choose KEMSO?

  • High Performance – Every KEMSO fuel pump is engineered to meet or exceed OEM specifications. They deliver the exact fuel pressure and flow rate your engine needs for optimal performance.
  • OEM Replacement – KEMSO pumps are designed as direct replacements for your vehicle’s original equipment. They fit perfectly, with no modifications required.
  • Lifetime Warranty – KEMSO stands behind every product with a lifetime warranty. If your pump ever fails, you are covered. This is a level of confidence that other brands simply do not offer.

Visit the KEMSO website today to find the exact fuel pump for your vehicle:

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KEMSO offers a wide range of fuel pumps for cars, motorcycles, ATVs, UTVs, and personal watercraft. Whether you drive a Ford, Chevrolet, Honda, Kawasaki, or Polaris, KEMSO has a pump that will get you back on the road safely.

How to Prevent the P0231 Code from Returning

Once you have fixed the issue, there are a few steps you can take to prevent it from happening again :

  1. Keep Your Fuel Tank at Least 1/4 Full – Running the tank low can cause the fuel pump to overheat, leading to premature failure.
  2. Use Quality Fuel – Poor quality fuel can contain contaminants that clog the pump and strain the electrical system.
  3. Inspect Wiring Regularly – If you live in an area with road salt or high humidity, check your fuel pump wiring for corrosion annually.
  4. Replace the Fuel Filter – A clogged fuel filter puts extra strain on the pump. Replace it according to your vehicle’s maintenance schedule.

Final Thoughts

The P0231 fuel pump secondary circuit low code is not something to ignore. It signals a problem with the electrical system that powers your fuel pump, and it can leave you stranded. The key is to diagnose it quickly and accurately.

If the diagnosis points to a failed fuel pump, do not settle for a cheap replacement. Choose a KEMSO fuel pump for the best combination of performance, fit, and warranty protection. Visit https://www.kemsoracing.com/ to find the right pump for your vehicle and get back on the road with confidence.


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