What is the difference between P0230 and P0231?

P0230 is the primary circuit — the low-current control wire between the computer and the fuel pump relay. P0231 is the secondary circuit — the heavy power feed from the relay to the pump motor itself. P0231 more often involves the pump, its wiring, or a blown fuse, while P0230 more often involves the relay coil and its control wire.

My fuel pump fuse keeps blowing. Is that related?

Very likely. A pump motor with shorted windings or worn brushes draws far more current than it should and pops the fuse, which the computer sees as a low secondary circuit. Measure the pump's current draw with a clamp meter before replacing anything — an over-spec reading condemns the pump.

Can a bad ground cause P0231?

Yes. The pump needs a clean ground path as much as it needs power. A corroded ground strap or a bad pin in the tank-top connector creates a voltage drop that keeps the pump from spinning up, and the computer reports the circuit as low. Always voltage-drop test the ground side before condemning the pump.

How much work is it to replace the fuel pump?

It depends entirely on the vehicle. Many trucks, SUVs, and sedans have an access panel under the rear seat or cargo floor, which makes it a one to two hour job. Others require dropping the fuel tank, which means draining fuel, supporting the tank, and disconnecting lines and straps — three to four hours and a job most people hand to a shop.

OBD-II trouble code

P0231: Fuel Pump Secondary Circuit Low

The engine computer commanded the fuel pump on but saw low or no voltage on the pump's power feed. Common causes are a failed relay, a corroded connector, or a shorted pump motor. The engine may crank without starting.

High severityPowertrainFuel & Air MeteringDo not drive

Quick facts

System: Powertrain
Category: Fuel & Air Metering
Severity: High severity
Drivable: No — stop driving until repaired
Repair cost range: $40 – $1,200
DIY difficulty: Advanced DIY

What does P0231 mean?

The secondary circuit is the high-current side of the fuel pump wiring — the heavy feed that runs from the fuel pump relay or pump control module, back through the vehicle, and into the pump motor in the tank. The engine control module monitors the voltage on that feed. When it commands the pump on, it expects to see near battery voltage there.

P0231 sets when the computer commands the pump on and the sensed voltage stays low — at or near zero — instead of rising. Something between the relay output and the pump is either not passing voltage or is dragging it down. An open circuit reads low because nothing is feeding the wire at all. A short to ground reads low because the voltage is being pulled down. A pump motor with shorted windings can draw so much current that the feed sags and the fuse blows.

Expect a no-start or a stall. Without a powered pump there is no fuel pressure, and the engine will crank normally but never fire. If the fault is intermittent — a corroded pigtail at the tank is the classic offender — the car may run fine until heat or vibration opens the connection, then quit. Do not drive a vehicle with P0231 stored.

Common causes

Blown fuel pump fuse, often blown by a shorted or worn pump motor drawing excess current
Fuel pump relay with burned or pitted contacts that will not pass current
Corroded or melted connector at the fuel pump module on top of the tank
Chafed pump feed wire shorted to ground along the frame rail or floor pan
Open in the heavy power feed between the relay and the pump
Failed fuel pump motor with shorted windings
Failed fuel pump driver/control module output stage

Symptoms

Engine cranks but will not start
No fuel pump prime when the key is turned to ON
Sudden stalling, sometimes with a restart after cooling down
Repeatedly blown fuel pump fuse
Zero or very low fuel pressure at the test port
Check engine light on

Diagnostic steps

1.Confirm P0231 and note companion codes — P0230 points more at the control side, P0232 is the opposite (high) fault.
2.Check the fuel pump fuse. If it is blown, replace it once and see whether it blows again immediately, which indicates a hard short or a seized pump motor.
3.Turn the key to ON and listen for the pump prime. Silence with a good fuse and relay pushes the fault toward the feed wire or the pump.
4.Back-probe the pump feed at the tank-top connector and measure voltage while the pump is commanded on. Near battery voltage there means the wiring is fine and the pump or its ground is the problem.
5.If voltage is missing at the tank, work backward: measure at the relay output terminal, then trace the feed wire for chafing, corrosion, or an open splice.
6.Perform a voltage-drop test on the powered side and on the pump's ground with the pump running — more than about half a volt of drop indicates a bad connection.
7.Measure fuel pump current draw with a clamp meter and compare to specification. Very high draw points at a failing pump motor; zero draw with good voltage points at an open pump or ground.

Repair cost

$40 – $1,200

A fuse and relay are $15-$60. Repairing a corroded tank-top connector or a chafed feed wire runs $150-$400. A full fuel pump module replacement is typically $120-$700 in parts plus 1.5-4 hours of labor — vehicles with an access panel under the rear seat are far cheaper than those where the tank must be dropped. Diagnosis alone is usually $75-$150.

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DIY vs shop

This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.