P0231 – Fuel Pump Secondary Circuit Low

P0231 is an OBD-II trouble code that points to a problem in the fuel pump circuit, specifically the low-voltage side that the ECU monitors. When this circuit doesn’t see the voltage it expects, the computer flags P0231 and usually turns on the check engine light. You might notice hard starting, stalling, or a no-start condition, especially when the fuel pump stops getting proper power. In many cases, the issue is wiring, a relay, or a bad connection rather than the fuel pump itself, but it must be checked carefully.

What Does P0231 Mean?

P0231 stands for “Fuel Pump Secondary Circuit Low.” In plain terms, your ECU is seeing lower-than-expected voltage on the fuel pump feedback or secondary circuit. The ECU uses this signal to confirm that the fuel pump relay and wiring are doing what they should when the pump is commanded on.

When the voltage drops below the calibrated threshold, the ECU assumes there’s an electrical fault: corroded connectors, damaged wiring, a failing relay, or sometimes a failing fuel pump drawing too much current. Left unchecked, this can lead to intermittent stalling or a complete no-start condition.

Quick Reference

• Code: P0231 – Fuel Pump Secondary Circuit Low
• Type: Electrical fault in fuel pump power/feedback circuit
• Common Symptoms: Hard start, no-start, stalling, low power
• Risk Level: Medium to high – can leave you stranded
• Typical Fixes: Repair wiring, replace fuel pump relay, fix grounds, sometimes replace fuel pump

Real-World Example / Field Notes

In the shop, I see P0231 most often on higher-mileage trucks and SUVs that have lived in rust-prone areas. One common pattern: the customer complains of random stalling or long cranking after fill-ups. The scan tool shows P0231, fuel pressure is low, but the pump itself tests OK on the bench. The real culprit usually ends up being a corroded connector at the frame rail or a weak ground near the fuel tank. Once the wiring is cleaned, repaired, and sealed, the code disappears and the starting issues are gone.

Symptoms of P0231

• Hard starting – Engine cranks longer than normal before it fires.
• No-start condition – Starter turns the engine, but it never actually starts.
• Intermittent stalling – Engine may die randomly at idle or while driving.
• Loss of power – Poor acceleration, especially under load or at highway speeds.
• Rough running – Misfires or rough idle due to inconsistent fuel pressure.
• Check engine light – MIL illuminated with stored P0231, sometimes accompanied by other fuel system codes.
• Fuel pump noise changes – Pump may sound weaker, louder, or cut in and out.

Common Causes of P0231

Most Common Causes

• Faulty fuel pump relay – Contacts inside the relay burn or stick, causing low or inconsistent voltage to the pump.
• Corroded connectors – Moisture and road salt corrode the fuel pump connector or intermediate harness plugs, increasing resistance.
• Damaged wiring – Chafed, pinched, or broken wires between the relay, ECU, and fuel pump, often along the frame rail.
• Bad ground connection – Loose or rusty ground near the fuel tank or on the chassis causes voltage drop under load.
• Weak fuel pump drawing high current – A failing pump can drag voltage down, triggering the “circuit low” code.

Less Common Causes

• Faulty fuel pump control module – On vehicles with a separate module, internal failure can prevent proper voltage output or feedback.
• ECU internal fault – Rare, but a damaged ECU driver or monitoring circuit can misread fuel pump voltage.
• Aftermarket alarm/remote start wiring – Poorly installed security systems spliced into the fuel pump circuit can cause voltage drops.
• Incorrect relay or fuse rating – Wrong replacement part can cause overheating, low voltage, or intermittent operation.
• Water intrusion – Flood damage or leaks soaking the harness or relay box can create intermittent low-voltage conditions.

Diagnosis: Step-by-Step Guide

To diagnose P0231 properly, you’ll want a basic scan tool, a digital multimeter (DMM), a test light, and ideally a wiring diagram for your specific vehicle. A fuel pressure gauge and backprobe pins are also very helpful. Always work safely around fuel vapors and disconnect the battery when repairing wiring.

1. Confirm the code and check for companions. Use a scan tool to read all stored and pending codes. Note any additional fuel system or powertrain codes (like P0230, P0232, lean codes) that can guide you.
2. Check fuel pump operation. Turn the key to ON and listen at the fuel tank area for a 2–3 second pump prime. No sound suggests a power, ground, or pump issue.
3. Inspect fuses and relay. Locate the fuel pump fuse and relay in the under-hood or interior fuse box. Check the fuse with a test light, then swap the relay with a known-good identical relay if available.
4. Verify power at the relay. With the key ON, use a multimeter or test light to confirm battery voltage at the relay power feed and signal terminals. If the relay never gets a control signal from the ECU, you may have an upstream issue.
5. Check voltage at the fuel pump connector. Safely access the connector at or above the fuel tank. Backprobe the power and ground wires with the pump commanded ON (using a scan tool or key cycle). You should see close to battery voltage. Low or no voltage points to wiring, relay, or ground problems.
6. Test ground integrity. Perform a voltage drop test between the pump ground wire and battery negative while the pump is running. More than about 0.1–0.2 volts drop indicates a poor ground connection.
7. Inspect wiring harness. Follow the harness from the relay/fuse box to the pump. Look for rubbed-through insulation, green corrosion, broken clips, or previous repairs with poor splices.
8. Check fuel pump current draw. If you have a clamp meter, measure pump current on the power wire. A pump drawing significantly more or less than spec can cause low voltage and trigger P0231.
9. Evaluate control module (if equipped). On vehicles with a fuel pump control module, verify proper power, ground, and command signals to the module before condemning the pump.
10. Use Mode $06 and live data. On some vehicles, Mode $06 or live data will show fuel pump duty cycle or feedback voltage. Abnormal readings under load can confirm an intermittent circuit issue.

Pro tip: When you find corrosion or a bad connector, don’t just clean the visible area. Cut back the harness until you reach clean, shiny copper, then solder and heat-shrink the repair to prevent the problem from coming back.

Possible Fixes & Repair Costs

Repairs for P0231 range from simple electrical fixes to full fuel pump replacement. A basic wiring repair or ground cleanup might cost $50–$200 in parts and labor at a shop. Replacing a fuel pump relay or fuse is usually $50–$150. If the fuel pump itself is failing and must be replaced, you’re typically looking at $400–$900 on most vehicles, and sometimes over $1,000 for certain trucks or European models. Costs vary based on vehicle design, labor rates, parts quality (OEM vs aftermarket), and whether the fuel tank must be dropped.

• Repair or replace corroded connectors and terminals.
• Repair damaged wiring and secure the harness away from sharp edges and heat.
• Clean and tighten fuel pump and chassis grounds.
• Replace faulty fuel pump relay or incorrect fuse/relay.
• Replace failing fuel pump assembly when current draw or pressure is out of spec.
• Replace or reprogram a faulty fuel pump control module (if equipped).

Can I Still Drive With P0231?

You might be able to drive for a short time with P0231, but it’s risky. Because this code involves the fuel pump power circuit, your engine can stall without warning or fail to restart after you shut it off. If the vehicle is running normally and the code is intermittent, drive only as needed and avoid long trips until it’s diagnosed. If you’re already experiencing stalling, hard starting, or loss of power, it’s safer to tow the vehicle to a shop rather than risk being stranded or causing an accident.

What Happens If You Ignore P0231?

Ignoring P0231 can turn a simple wiring or relay repair into a bigger, more expensive problem. A weak connection can overheat and damage the harness, connectors, or even the fuel pump itself. You also run the risk of sudden stalling in traffic, which is a safety concern. Over time, repeated low fuel pressure events can stress injectors and cause lean-running conditions that may damage the engine or catalytic converter.

Last updated: January 22, 2026

Vehicles Commonly Affected by P0231

P0231 shows up across many makes, but I see it most often on domestic trucks and SUVs that use frame-mounted harnesses and external fuel pump modules. Ford F-150, Expedition, Explorer, and E-Series vans are frequent visitors, as are GM trucks and SUVs like Silverado, Sierra, Tahoe, Suburban, and Yukon. Dodge/Ram pickups and some Jeep models also commonly log this code, especially in rust-belt regions. Compact cars from Ford, Chevrolet, and some European brands can see P0231 as well, particularly where the fuel pump wiring runs under the rear seat or along the underbody.