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Severity: High Code type: Generic (all makes) ✱

P0231 Code: Fuel Pump Secondary Circuit Low

Voltage on the wire feeding the fuel pump is too low while the pump is supposed to be running.

Unverified: this manufacturer-specific definition comes from a single source or varies by model. Confirm it with a brand-specific scan tool.

Safety first · Consult a professional

  • Fuel vapor is flammable. No smoking or open flames; work outdoors and fix fuel leaks before driving.

At a glance

Severity: 4/5 – High4/5

Severity: High

Meaning
Fuel Pump Secondary Circuit Low
System
Fuel & Air Metering · Powertrain
Safe to drive?
With caution
Typical repair cost
$20–$1,200
DIY difficulty
Moderate

The 'secondary' circuit is the power side: the heavy wire that runs from the relay or fuel pump driver module back to the pump in the tank. Many PCMs monitor the voltage on that wire, and P0231 means it stayed low while the PCM was commanding the pump on. Either power isn't getting through, because of burned relay contacts, a blown pump fuse or an open feed wire, or the pump is drawing so much current that it drags the voltage down. The weak spot is often the connector on top of the tank, where years of pump current can overheat and melt the terminals. Unlike the control-side code P0230, this one points you toward the pump, its wiring and its connections rather than the relay coil.

How to read P0231

How to read P0231P10223314
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 2 Fuel & air (injector circuit)
  4. 31 Specific fault

Symptoms

  • Engine dies while driving, sometimes restarting after it cools
  • Crank-no-start with no pump hum at key on
  • Surging or hesitation at highway speed as pump voltage sags
  • Fuel pump fuse found blown, or blowing again after replacement
  • Lean codes or low fuel pressure codes stored alongside
  • Burnt smell or discolored plastic at the tank-top connector

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Worn fuel pump drawing excessive current and pulling the feed voltage down 26%
  2. Melted or corroded connector on the fuel pump module at the top of the tank 22%
  3. Burned relay contacts or a failing driver module output 18%
  4. Blown pump fuse or loose fuse terminal 14%
  5. Open or high-resistance feed or ground wire to the pump 14%
  6. Low system voltage from a weak battery or charging fault 6%

Diagnosis step by step

Diagnostic flow: P02311Check the fuse and its terminals2Measure voltage at the pump underload3Voltage-drop the relay and ground4Check pump current draw5Inspect the tank-top connector

  1. Check the fuse and its terminals

    Inspect the pump fuse and the fuse box terminal it plugs into. A fuse that looks fine but has a heat-browned or loose terminal can drop voltage under load. If the fuse is blown, don't just replace it; something drew too much current.

    Tools: Flashlight, Pliers

  2. Measure voltage at the pump under load

    Back-probe the pump feed at the tank connector with the pump running (engine idling or relay jumpered). You should see within about 0.5 volt of battery voltage. A bigger gap means resistance somewhere between the battery and the pump.

    Tools: Multimeter

  3. Voltage-drop the relay and ground

    Measure across the relay's switched contacts (terminals 30 and 87) while the pump runs; more than about 0.2 volt means burned contacts. Then measure from the pump ground wire to the battery negative post; more than 0.1 volt points to a corroded ground.

    Tools: Multimeter

  4. Check pump current draw

    With an inductive amp clamp or a fused ammeter in series, most gasoline in-tank pumps draw roughly 4 to 10 amps depending on design. A reading well above spec, or one that climbs as the pump warms, means the pump is binding and is the root cause.

    Tools: Multimeter

  5. Inspect the tank-top connector

    Access the pump module through the rear-seat hatch or by lowering the tank. Look for melted plastic, blackened pins or a connector that has been hot enough to deform. Replace the pigtail along with the pump, because a burned connector will cook a new pump's terminals too. Keep sparks and flames away while the tank is open.

    Tools: Flashlight, Screwdriver, Gloves

Where the parts are

Charging system and control modules – P02311234567
Charging system and control modules
  1. 1Battery
  2. 2Alternator
  3. 3Engine computer (ECM)
  4. 4CAN bus
  5. 5Transmission
  6. 6Wheel speed sensor
  7. 7High-voltage battery

Repair options & costs

RepairDIY?Estimated cost
Fuse and fuse box terminal repair Yes $20–$150
Fuel pump relay replacement Yes $20–$90
Tank-top connector pigtail replacement No $80–$300
In-tank fuel pump module replacement No $450–$1,200
Fuel pump driver module replacement Yes $150–$500

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Emissions / smog test impact

Will fail

With the check engine light on, the car fails an OBD-II emissions test. A pump that sags under load may also leave the engine running lean enough to set other emissions codes, so fix the supply before testing.

Frequently asked questions

What's the difference between primary and secondary circuit?

The primary circuit is the low-current control side the PCM uses to switch the relay or driver module. The secondary circuit carries the actual pump current. P0231 therefore points toward the pump, its wiring, connectors and relay contacts, not the relay coil.

Can a failing pump really cause an electrical code?

Yes. As a pump wears it binds and draws more current. That extra current causes bigger voltage drops across every connection and the relay, and the PCM sees the feed voltage sag below its threshold.

The fuse keeps blowing. What now?

A repeatedly blowing pump fuse means either a seized pump or a feed wire shorted to ground, often where it runs over the tank or along the frame. Measure pump current and check the wire for chafing before fitting another fuse.

Should I replace the connector with the pump?

If it shows any heat damage, yes. A burned terminal has high resistance that heats up again under load and can ruin the new pump's connector within weeks.

Sources