P2404 Evaporative Emission System Leak Detection Pump Sense Circuit Range/Performance

P2404 is an OBD-II diagnostic trouble code associated with the EVAP leak detection pump sense circuit. The engine control module (ECM/PCM) has detected that the signal coming from, or associated with, the leak detection pump's sensing circuit is outside the expected range or is not behaving as expected.

Unlike P2402, which points toward a high electrical condition in the pump control circuit, P2404 is concerned with the sense/feedback side of the leak detection system.

That distinction matters.

The ECM needs to know not only whether it can command the leak detection pump, but also whether the pump and its associated sensing system are producing a believable response. P2404 indicates that this feedback does not match what the control module expects.

What Is the EVAP Leak Detection Pump?

The evaporative emission control system prevents gasoline vapors from escaping into the atmosphere.

A typical EVAP system may contain:

• Fuel tank

• Charcoal canister

• Purge valve

• Vent valve

• Leak detection pump

• Pressure or pressure-switch circuitry

• Fuel tank pressure sensor

• EVAP vapor lines

• ECM/PCM

The exact arrangement varies between manufacturers.

During an EVAP self-test, the vehicle may use a leak detection pump to create a controlled pressure or vacuum in the vapor system. The ECM then observes the resulting pressure behavior to determine whether the system is sealed.

The sense circuit provides information about what is happening during this process.

If the feedback does not correspond to the expected operating range, P2404 can be stored.

What Does “Range/Performance” Mean?

The phrase Range/Performance is important.

It does not necessarily mean that the circuit is completely open or shorted.

Instead, the ECM has determined that the signal:

• Is outside its expected operating range

• Does not respond correctly when the pump is commanded

• Changes in an unexpected way

• Does not correspond to the expected EVAP pressure condition

• Behaves inconsistently with the vehicle's operating strategy

For example, the ECM may command the leak detection pump to operate and expect a particular feedback response.

If the pump operates but the sense signal does not change as expected, the ECM can determine that the system's performance is abnormal.

This is different from simply saying that the circuit has no voltage.

P2404 Does Not Automatically Mean an EVAP Leak

This is one of the most important points when interpreting the code.

P2404 is not simply a physical EVAP leak code.

A cracked EVAP hose, damaged fuel cap, or leaking canister can certainly affect the pressure behavior of the system, but P2404 specifically concerns the range/performance of the leak detection pump's sense circuit.

The actual problem could therefore be electrical, mechanical, pneumatic, or a combination of these.

Possible causes include:

• Faulty leak detection pump

• Faulty pump sense circuit

• Pressure sensor problem

• Damaged wiring

• Corroded connector

• Poor terminal connection

• Restricted EVAP line

• Blocked vent path

• Mechanical problem inside the pump

• Incorrect EVAP component

• Physical EVAP leak

• Wiring resistance

• Power or ground problem

• ECM/PCM fault

Diagnosis has to determine which of these is actually responsible.

The Difference Between Control and Sense Circuits

The distinction between P2402 and P2404 becomes much clearer when the two circuits are considered separately.

The control circuit is used by the ECM to command the leak detection pump.

The sense circuit provides feedback about what the pump or EVAP system is doing.

Think of it as:

ECM command → pump operates → EVAP pressure changes → sense circuit reports the result → ECM evaluates the response

If the ECM cannot properly command the pump, the problem may be on the control side.

If the pump can be commanded but the feedback is outside the expected range, P2404 becomes more relevant.

This is why replacing the pump without testing the feedback circuit can result in an unnecessary repair.

Common Causes of P2404

Faulty leak detection pump

The pump assembly may have an internal electrical or mechanical problem.

It may operate partially but fail to generate the expected pressure or feedback signal.

Faulty sense circuit

The sensing portion of the system may be producing an incorrect signal even though the pump itself is capable of operating.

Damaged wiring

A wire with excessive resistance, intermittent continuity, or insulation damage can distort the feedback signal.

The wiring underneath the vehicle is particularly vulnerable to:

• Road debris

• Moisture

• Corrosion

• Heat

• Vibration

• Physical impact

• Previous repairs

Connector or terminal problems

A connector may be contaminated, corroded, loose, or damaged.

A poor terminal connection can change the electrical characteristics of the sense circuit without creating a complete open circuit.

EVAP pressure sensor problem

Some vehicles use pressure sensing as part of the leak detection strategy.

If the pressure information is incorrect, the ECM may determine that the pump's feedback does not match the expected behavior.

Restricted EVAP plumbing

A blocked vapor line, vent path, filter, or canister can prevent the pressure response from developing normally.

This can make a functioning pump appear to be performing incorrectly.

Physical EVAP leak

A significant leak can prevent the system from achieving or maintaining the expected pressure.

Although P2404 is not simply a leak code, the physical sealing of the EVAP system still needs to be considered when the pump and sense circuitry test correctly.

Incorrect replacement component

An aftermarket or incorrect EVAP component may physically fit but have different electrical or pressure characteristics.

Power or ground problem

A weak power supply or poor ground can affect pump operation and feedback.

ECM/PCM fault

An internal control-module problem is possible but should generally be considered only after the external components and circuits have been tested.

Symptoms of P2404

P2404 may produce very few noticeable symptoms.

The vehicle's engine does not normally depend on the EVAP leak detection system to maintain basic operation.

Possible symptoms include:

• Check Engine Light

• Failed emissions inspection

• EVAP monitor not ready

• EVAP self-test failure

• Occasional fuel vapor odor

• Other EVAP-related codes

• No obvious drivability symptoms

In many cases, the driver notices the Check Engine Light but cannot feel anything wrong with the engine.

That does not mean the code should be ignored. It indicates that the emissions-monitoring system is not operating correctly.

Why a Vehicle Can Run Normally With P2404

The EVAP system primarily controls fuel vapors rather than engine torque.

The engine can therefore run smoothly even when the leak detection system has a serious fault.

The ECM can continue operating the engine using its normal fuel and ignition strategies while the EVAP monitor remains unsuccessful.

This explains why P2404 can be present without:

• Rough idle

• Loss of power

• Poor acceleration

• Stalling

If other codes are present, however, those codes may point toward a broader electrical or engine problem.

How P2404 Should Be Diagnosed

A good diagnosis starts with the feedback circuit, not by replacing the pump immediately.

Start With a Complete Scan

Check all stored and pending codes.

Look for related faults involving:

• EVAP pressure

• EVAP purge

• EVAP vent

• Leak detection

• Fuel tank pressure

• Electrical supply

• Ground circuits

• Communication

• Battery voltage

If P2404 appears with another EVAP code, the second code may explain why the sense signal is behaving incorrectly.

Check Freeze-Frame Data

Freeze-frame information can show the conditions under which the ECM detected the fault.

Depending on the vehicle, useful information may include:

• Engine coolant temperature

• Engine RPM

• Vehicle speed

• Fuel level

• Ambient temperature

• System voltage

• EVAP pressure

• Pump command

• Sensor feedback

Some EVAP monitors only operate under specific temperature and fuel-level conditions, so this information can be valuable.

Identify the Exact EVAP System Design

Not every manufacturer uses the same leak detection pump.

The pump may be:

• A standalone component

• Integrated into a vent assembly

• Combined with pressure-sensing hardware

• Mounted near the charcoal canister

• Located close to the fuel tank

The wiring diagram and service documentation should be used to identify the exact sense circuit.

Do not assume that a component called a “leak detection pump” operates identically across different vehicles.

Inspect the Pump and Connector

Look for:

• Water intrusion

• Corrosion

• Broken locking tabs

• Bent terminals

• Loose terminals

• Damaged wiring

• Contamination

• Physical damage

Because EVAP components are often mounted underneath the vehicle, connector corrosion is worth taking seriously.

Test the Sense Circuit

The next step is to identify the sense wire and determine how the ECM expects it to behave.

Depending on the system, testing may involve:

• Reference voltage

• Ground

• Signal voltage

• Continuity

• Resistance

• Voltage drop

• Signal response

• Current

• Scan-tool data

There is no universal P2404 voltage or resistance specification.

The correct values depend on the vehicle's EVAP design.

A measurement that looks “normal” on one vehicle may be completely incorrect on another.

Compare Commanded Operation With Feedback

This is often the most useful part of the diagnosis.

If the scan tool supports EVAP active tests, the technician can command the leak detection pump and observe the response.

The question is not simply:

“Does the pump run?”

It is:

“Does the pump produce the expected system response, and does the sense circuit report that response correctly?”

For example, a pump may make an audible operating sound but fail to generate the required pressure.

Alternatively, the pump may create the correct pressure while the sense circuit reports an incorrect value.

Those are two different faults.

Check the EVAP System for Restrictions

If the electrical circuit checks out, examine the physical EVAP system.

A blocked vent, restricted vapor line, saturated canister, or other restriction can interfere with the pressure response.

The technician should verify that the system can move air/vapor as designed.

Check for Physical EVAP Leaks

Once the pump and sense circuit are functioning correctly, physical sealing becomes increasingly important.

A smoke test can help locate leaks in:

• EVAP hoses

• Fuel tank connections

• Charcoal canister

• Vent valve

• Purge plumbing

• Filler neck

• Fuel cap area

However, a smoke test should not be used as a substitute for electrical diagnosis when the primary complaint is a sense-circuit range/performance fault.

Pressure Testing Can Provide the Missing Answer

If the pump operates and the electrical signal appears correct but the system still does not behave properly, pressure testing can help separate the possibilities.

The technician can determine whether:

• The system reaches the required pressure

• Pressure builds too slowly

• Pressure falls too quickly

• Pressure cannot be generated

• The system becomes over-restricted

The manufacturer's test procedure and pressure limits should always be followed.

P2404 and the Fuel Cap

The fuel cap is often blamed whenever an EVAP code appears.

A damaged or incorrectly installed fuel cap can certainly create EVAP leaks.

However, replacing the fuel cap should not be considered the automatic repair for P2404.

P2404 is specifically associated with the leak detection pump sense circuit range/performance.

If the cap is visibly damaged or incorrect, it should be repaired, but the pump and feedback circuit still need to be evaluated.

Could a Small EVAP Leak Cause P2404?

It is possible for physical EVAP problems to influence the pressure response that the leak detection system observes.

However, a small leak does not automatically explain a sense-circuit range/performance code.

If the vehicle also has a leak-related DTC such as P0456, the diagnostic direction becomes clearer.

In that situation, the technician should determine whether the physical leak is causing the abnormal test result or whether there are two separate faults.

P2404 vs P2402

These codes involve different aspects of the leak detection pump system.

P2402 – EVAP Leak Detection Pump Control Circuit High

The ECM detects an electrically high condition in the pump control circuit.

The focus is primarily on electrical control.

P2404 – EVAP Leak Detection Pump Sense Circuit Range/Performance

The ECM detects that the pump's sense/feedback signal is outside its expected range or is not behaving correctly.

The focus is on the feedback side of the system.

A P2402 diagnosis therefore tends to begin with control-circuit voltage and wiring, while P2404 requires closer attention to the sense signal and the response of the EVAP system.

P2404 vs P2400

P2400 indicates an open condition in the leak detection pump control circuit.

P2404 indicates a range/performance problem involving the pump's sense circuit.

An open control circuit can prevent the pump from operating at all.

A sense-circuit problem can occur even when the pump is capable of operating.

P2404 vs P0456

These codes can be confused because both may involve the EVAP leak-testing process.

P2404 focuses on the leak detection pump's sense/feedback performance.

P0456 indicates that the EVAP system has detected a very small leak.

A vehicle can have one without the other.

This is why the complete set of stored and pending DTCs should always be considered.

Is It Safe to Drive With P2404?

For most vehicles, P2404 does not create an immediate drivability or engine-damage risk.

If the engine runs normally and there is no fuel leakage or strong fuel odor, the vehicle can often be driven to a repair facility.

However, the problem should not be ignored indefinitely.

The vehicle may fail an emissions inspection because the EVAP monitor cannot complete successfully.

If you notice raw fuel odor, visible fuel leakage, or a damaged fuel-system component, stop treating the problem as a simple emissions fault and have the vehicle inspected promptly.

Is the Leak Detection Pump the Most Likely Failed Part?

Not necessarily.

The pump is only one part of the system.

The actual repair could involve:

• Leak detection pump

• Sense circuit

• Pressure sensor

• Wiring

• Connector

• Terminal

• Power supply

• Ground

• EVAP hose

• Vent path

• Charcoal canister

• Incorrect component

• ECM/PCM in rare cases

Replacing the pump before checking the sense circuit can therefore be an expensive guess.

A More Reliable Diagnostic Sequence

For P2404, the diagnostic process can be organized around one question:

Does the ECM receive the feedback it expects when the leak detection system operates?

A practical sequence is:

Scan all codes and inspect freeze-frame data.

Identify the exact leak detection pump and sense circuit for the vehicle.

Inspect the pump, connector, and wiring.

Verify the circuit's power, ground, and signal according to manufacturer specifications.

Use a scan tool to command the pump when supported.

Observe pump operation and sense-circuit feedback simultaneously.

Check for restrictions in the EVAP system.

Check the EVAP system for physical leaks if the electrical system is functioning correctly.

Clear the code and verify the EVAP monitor completes successfully.

This approach separates an electrical feedback problem from a genuine pressure/sealing problem.

What the Repair May Look Like

Once the fault has been identified, the solution may be relatively simple.

Possible repairs include:

• Repairing damaged wiring

• Replacing a corroded connector

• Repairing a terminal

• Replacing the leak detection pump

• Replacing an integrated pressure/sense component

• Repairing an EVAP hose

• Correcting a blocked vent

• Replacing a faulty pressure sensor

• Repairing an EVAP leak

• Correcting an incorrect component installation

• Repairing an ECM circuit in rare cases

After the repair, the EVAP monitor may need to complete its specific drive cycle before the vehicle's readiness status returns to normal.

The Most Important Diagnostic Point

P2404 does not tell you that “the EVAP pump is bad.”

It tells you that the ECM is unhappy with the range or performance of the signal it receives from the leak detection pump's sense circuit.

That signal can be wrong because the electrical circuit is faulty, the sensing component is faulty, the pump is not producing the expected pressure, or the EVAP system itself has a restriction or leak.

That is why a good diagnosis follows the entire chain:

Command → pump operation → pressure response → sense signal → ECM interpretation.

Once those stages are tested individually, P2404 becomes much easier to diagnose without unnecessarily replacing EVAP components.