OBD-II Code P2404: EVAP Leak Detection Pump Sense Circuit Problem

What Does P2404 Mean?

Your car's Engine Control Unit (ECU) detected an electrical problem with the EVAP system's leak detection pump. This pump pressurizes the fuel system to test for vapor leaks. Code P2404 means the electrical feedback signal from the pump is out of its expected range, preventing the test from running.

Technical definition: The SAE/OBD-II definition is "Evaporative Emission System Leak Detection Pump Sense Circuit Range/Performance". The powertrain control module (PCM) detected the electrical signal from the leak detection pump's internal sensor is outside the expected 0.5V-5.0V range, is unstable, or contradicts the pump's commanded state. The 'sense circuit' is the feedback line verifying pump operation.

Can I Drive With P2404?

Yes, But With Caution. Driving is safe and won't cause engine damage, but your car will fail an emissions test. The primary risks are releasing excess fuel vapors and masking a real EVAP system leak. On newer vehicles, especially Subarus, this code disables advanced safety features like EyeSight and automatic emergency braking until repaired.

Common Causes

• Outdated Engine Control Module (ECM) Software (Very Common) — On modern Subarus and Toyotas, the original computer software is too sensitive and incorrectly triggers P2404 when condensation causes the pump to seize temporarily in cold weather. A dealership software update resolves this by adjusting how the computer interprets pump signals.
• Faulty EVAP Leak Detection Pump (LDP/ELCM/DMTL) (Very Common) — The pump assembly is the most frequent physical failure point. The internal motor seizes, the integrated electronic sensor fails, or moisture intrusion destroys the circuitry.
• Damaged Wiring, Connectors, or Grounds (Common) — Located underneath the vehicle, the pump's wiring is vulnerable to road salt, moisture, and debris. Corrosion on the connector pins, a broken wire, or a loose ground point disrupts the 5V reference signal back to the ECU.
• Faulty Power Supply Relay (VW/Audi) (Less Common) — On Volkswagen and Audi models, the J757 Engine Component Power Supply Relay powers the leak detection pump. Relay failure is a known cause for P2404 on these vehicles and requires testing before replacing the pump.
• Clogged or Dirty LDP Air Filter (Less Common) — The leak detection pump draws clean air through a small filter. A clogged filter prevents the pump from pressurizing the system correctly, altering its electrical draw and triggering a performance range error.
• Saturated Charcoal Canister (From 'Topping Off') (Rare) — Consistently overfilling the gas tank forces liquid fuel into the charcoal canister and EVAP lines. This saturates the canister and floods the leak detection pump, causing internal electrical failure.
• Blocked or Restricted EVAP Lines (Rare) — A severe physical blockage in an EVAP line forces the pump to work outside its normal load range, spiking its electrical draw and triggering a performance fault.
• Faulty Powertrain Control Module (PCM) (Very Rare) — The PCM itself has an internal fault in the circuit reading the LDP sensor. Consider this only after definitively ruling out software, wiring, relays, and the pump.

Symptoms

• Check Engine Light is On — The light illuminates steadily on the dashboard. This is often the only noticeable symptom.
• Safety Systems Disabled — On Subarus and some Toyotas, this code triggers a warning and disables EyeSight, Reverse Automatic Braking (RAB), and automatic high beams as a default safety precaution.
• Failed Emissions Test — The vehicle automatically fails a smog inspection because the EVAP system monitor remains in a 'Not Ready' state.
• Slight Fuel Odor — You notice a faint smell of gasoline vapors near the rear of the vehicle, though this is less common than with physical leak codes.
• Occasional Rough Idle — Unmetered vapors enter the engine due to a stuck EVAP valve, causing a slightly unstable idle.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Update Engine Control Module (ECM) Software — Parts: $0, Labor: $80-$200 (Often free under 8yr/80k emissions warranty), ~1.0 hr book time (Professional)
• Replace EVAP Leak Detection Pump — Parts: $90-$200, Labor: $100-$200, ~1.5 hr book time (Intermediate)
• Repair Damaged Wiring or Replace Connector — Parts: $10-$50, Labor: $150-$300, ~2.0 hr book time (Intermediate)
• Replace EVAP System Power Relay (VW/Audi) — Parts: $20-$50, Labor: $50-$100, ~0.5 hr book time (Beginner)
• Replace Charcoal Canister — Parts: $200-$500, Labor: $100-$200, ~1.2 hr book time (Intermediate)

Used vs. New Parts: Buying Guide

When a used part is worth it: Buying a used OEM leak detection pump from a low-mileage vehicle is a cost-effective alternative to a new aftermarket part for older vehicles.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify the donor vehicle was not scrapped for emissions-related failures.
• Avoid parts from the 'Rust Belt' as connectors are prone to corrosion.
• Match the part number exactly.

Decision logic:

• If A known software update (TSB) is the likely cause (e.g., Subaru) → Do not buy any part. Get the software update first.
• If The cost of a new OEM or quality aftermarket pump is under $150 → Buy new for the warranty and guaranteed compatibility.
• If Vehicle is over 10 years old and the budget is tight → A used OEM part is a reasonable choice, accepting the risk of a shorter lifespan.

Warranty tradeoff: Used parts come with a 30-90 day warranty. New aftermarket parts offer a 1-year to limited lifetime warranty. New OEM parts carry a 1-year warranty.

Worst-case if a used part fails: $150-$300 if a used part fails shortly after installation, requiring a second replacement and labor charge.

What Happens If You Wait — Timeline

1. 0-1 month: Check Engine Light illuminates. The EVAP readiness monitor will not complete. On Subarus, EyeSight and safety systems are disabled. (MPG impact: 0%% · Added cost: $0)
2. 1-6 months: The vehicle automatically fails state emissions inspections. The car cannot detect new EVAP system leaks. (MPG impact: 0-1%% · Added cost: $50-$150 in re-inspection fees.)
3. 6-18 months: Intermittent electrical issues (like corrosion) worsen, potentially affecting other sensors sharing the same ground circuit. (MPG impact: 1-3%% · Added cost: $0-$200 if a secondary wiring problem develops.)
4. 18+ months: Long-term neglect prevents legal vehicle registration. If fuel saturation caused the failure, the charcoal canister requires replacement. (MPG impact: 1-3%% · Added cost: $250-$700 for a new charcoal canister.)

Cost of Not Fixing It

• 0-6 months: Guaranteed failure of state emissions inspections. Advanced safety systems (like Subaru EyeSight) remain disabled. The car releases excess fuel vapors. (Added cost: Negligible, aside from re-inspection fees.)
• 6-12 months: Masks a new, real EVAP leak (e.g., cracked hose) because the leak testing system is broken. Leads to a minor decrease in fuel efficiency. (Added cost: $50-$300 if a secondary leak develops and requires repair.)
• 12+ months: Inability to legally register the vehicle in states with emissions testing. Long-term neglect does not cause catastrophic engine damage. (Added cost: No direct repair costs, but the vehicle cannot be legally operated.)

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs)
   Check for TSBs related to code P2404 using your VIN. Manufacturers like Subaru and VW issue software updates that fix this exact problem without replacing parts.
   Tools: Phone, VIN, access to NHTSA database or dealership (Beginner)
2. Visually Inspect Wiring and Connectors
   Raise the vehicle and locate the EVAP leak detection pump near the rear charcoal canister. Inspect the electrical connector and wiring harness for green corrosion, frayed wires, or loose ground bolts.
   Tools: Jack, jack stands, flashlight (Beginner)
3. Check Fuses and Relays
   Locate the fuse for the EVAP system in your owner's manual and verify it is intact. For VW/Audi vehicles, locate and test the J757 power supply relay.
   Tools: Owner's manual, fuse puller, multimeter (Beginner)
4. Inspect the LDP Air Filter and Drain Tube
   Inspect the small air filter attached to the leak detection pump for dirt blockages. Check the drain tube for signs of water or oil intrusion.
   Tools: Flashlight, basic hand tools (Intermediate)
5. Test the Pump Circuit with a Multimeter
   Unplug the pump's connector with the key ON. Use a multimeter to verify 12V at the power pin and continuity to ground on the ground pin.
   Tools: Multimeter, vehicle-specific wiring diagram (Intermediate)
6. Command the Pump On with a Scan Tool
   Use a bi-directional scan tool to perform an 'Active Test' on the leak detection pump. If the pump runs but the sensor voltage stays out of range, the pump is faulty. If it doesn't run, the pump motor or power circuit is dead.
   Tools: Bi-directional OBD-II scan tool (Advanced)
7. [PRO TIP] Advanced Sense Circuit Voltage Testing
   Back-probe the sense circuit wire at the pump connector. With the key ON, verify the 5V reference signal. Command the pump ON; the voltage must change. An unchanging voltage confirms a failed internal pump sensor.
   Tools: Multimeter with back-probe pins, wiring diagram (Advanced)
8. [PRO TIP] Verify Live Data PIDs
   Monitor the 'EVAP System Vapor Pressure' PID on a scan tool. Normal operation shows small pressure changes (+/- 0.75 InHg). A stuck or nonsensical reading points directly to a sensor failure.
   Tools: Bi-directional OBD-II scan tool (Advanced)
9. [PRO TIP] Check Specific Resistance Values (VW/Audi)
   Measure resistance on the VW/Audi V144 pump connector. Pins 1 to 3 should read ~680 Ohms; pins 2 to 3 should read ~16 Ohms. Significant deviation requires pump replacement.
   Tools: Multimeter, wiring diagram (Advanced)
10. [PRO TIP] Analyze the Sense Circuit with an Oscilloscope
    Connect an oscilloscope to the sense circuit signal wire. Command the pump ON and verify the waveform matches the service manual pattern. Excessive noise or a flat line isolates the fault to the circuit or sensor.
    Tools: Automotive oscilloscope, wiring diagram (Professional)

When This Code Triggers (Freeze-Frame Conditions)

• Engine Coolant Temp: 4-30°C (39-86°F) (At startup for a cold soak test. The test may also run when the engine is fully warmed up.)
• Fuel Level: 15-85% (The EVAP monitor will not run if the tank is too full or too empty.)
• Vehicle Speed: 40-65 mph (64-105 kph) (Steady cruising for several minutes is required.)
• Ambient Air Temperature: 4-35°C (39-95°F) (The test is disabled in very hot or very cold weather.)

Related Codes

• P2401 — P2401 is 'Pump Control Circuit Low'. The ECU's command to turn the pump ON isn't working due to an open or short-to-ground. P2404 means the pump turns on, but the feedback signal is wrong. If both are present, suspect a damaged wiring harness.
• P2402 — P2402 is 'Pump Control Circuit High', indicating a short to power in the control circuit. P2402 points specifically to a wiring short, whereas P2404 points to a faulty feedback signal internal to the pump.
• P0442 / P0456 — These codes indicate a confirmed physical vapor leak. P2404 indicates the system that tests for leaks is electrically broken. Fix P2404 first, as the vehicle cannot detect physical leaks until the pump operates correctly.
• P2407 — P2407 is 'Pump Sense Circuit Intermittent/Erratic'. While P2404 indicates the signal is consistently out of range, P2407 suggests the signal is unstable or glitching. The diagnostic process is identical.

Climate & Environmental Factors

• Cold Weather / Condensation: Moisture accumulates inside the leak detection pump and freezes, causing temporary seizure of the internal motor. This seizure causes an out-of-range electrical reading, triggering P2404. Subaru software updates specifically address this sensitivity.
• High Humidity: High humidity increases moisture drawn into the EVAP system through the air filter, contributing to water collection and corrosion of the pump's electronics over time.
• Road Salt / Corrosion: In Rust Belt regions, the wiring harness and electrical connector for the leak detection pump are highly susceptible to salt corrosion. Salt spray attacks the copper pins, leading to high resistance circuits that directly cause P2404.

How to Talk to a Mechanic About This Code

Say this: "I have a P2404 code. If it's a Subaru, please check for TSBs regarding an ECM software update before replacing parts. If it's a VW or Audi, please check the J757 power relay first. For other makes, I need a diagnosis of the pump's power, ground, and sense circuit."

This signals you are aware of the most common misdiagnosed causes. It directs the technician toward cost-effective fixes first, preventing you from paying for a new pump when the issue is software or a relay.

Avoid saying:

• 'My check engine light is on, can you look at it?' (Too vague, invites a costly broad diagnosis.)
• 'Just replace the EVAP pump.' (Invites paying for a part you don't need.)
• 'I think I have an EVAP leak.' (P2404 is an electrical code, leading to an unnecessary smoke test.)

Questions to ask before authorizing the repair:

• For a Subaru: Did you confirm my vehicle's software is up-to-date according to the latest TSBs for P2404?
• For a VW/Audi: Did you test the J757 power supply relay and confirm it's working correctly?
• If recommending a pump replacement: What were the voltage and ground readings at the pump connector?
• Can you confirm you tested the sense circuit signal and it was out of spec?
• What is the warranty on this specific repair?

Where to Take It: Dealer vs Independent vs Chain

• Dealer:
  Best for: Subaru vehicles requiring a dealer-only ECM software update., Vehicles under the Federal 8yr/80k or PZEV 15yr/150k emissions warranty., Complex, make-specific electrical issues.
  Downsides: Highest labor rates., Long wait times for service. (Typical cost: +50% vs. baseline)
• Independent Shop: Best for non-Subaru, out-of-warranty repairs. For Subarus, go to the dealer first for the software update.
  Best for: Out-of-warranty vehicles where the cause is a failed pump, wiring, or relay., Diagnosing and repairing wiring or connector damage.
  Downsides: Quality varies widely; vet shops based on ASE certifications., May lack specific tools to perform ECM software updates. (Typical cost: +0% vs. baseline)
• Chain Shop: AVOID for this code. The diagnostic nuance required for P2404 is often missed, making incorrect repairs highly likely.
  Best for: Simple, routine maintenance like oil changes.
  Downsides: Technician skill varies dramatically., High pressure to upsell parts leads to misdiagnosis. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost exceeds 40-50% of the car's private-party value, consider selling or trading in the vehicle instead of repairing it.

• Car worth $3000, fix is $650: Fix it. The repair cost is ~22% of the car's value.
• Car worth $2500, fix is $1200: Walk away. The repair cost is 48% of the car's value. It's not financially sound to invest this much into an older vehicle for an emissions component.
• Car worth $15000, fix is $650: Fix it. The repair is a minor cost relative to the vehicle's high value.

What Scan Tool You Need for This Code

Minimum: A scanner with bidirectional control ('Active Test') to command the EVAP leak detection pump on and off.

A basic $20 code reader only tells you the P2404 code is present. It cannot command the pump to run, which is critical to determine if the pump or its wiring has failed.

Budget: BlueDriver Pro (~$100) — Reads live data from the EVAP system and offers enhanced system tests, a significant step up from basic readers.

Mid-range: Foxwell NT510 Elite (~$180) — Provides make-specific bidirectional control, allowing you to perform the crucial 'Active Test' to command the pump on and off.

Professional: Autel MaxiCOM MK808 (~$500) — Offers professional-level bidirectional control, runs the EVAP system test, and provides robust live data graphing to definitively diagnose circuit failures.

Rent vs buy: You can borrow a basic code reader for free from auto parts stores to confirm the code. However, these loaner tools lack the bidirectional control needed for a full DIY diagnosis. You must buy a capable scanner to diagnose P2404 yourself.

How to Clear the Code After You Fix It

1. Fix the underlying mechanical or electrical fault.
2. Use an OBD-II scan tool to clear the active and pending codes.
3. Perform the specific EVAP drive cycle required for your vehicle to clear the 'Permanent DTC'.

Drive cycle (~30 minutes): A general EVAP drive cycle involves: a cold start (sit for 8+ hours), idle for 2-5 minutes, drive at a steady highway speed (55 mph) for 5-10 minutes, perform stop-and-go city driving, and let the vehicle sit again.

Readiness monitors affected: EVAP System Monitor, Oxygen Sensor (O2) Monitor, Catalyst Monitor

Before emissions retest: drive at least 100 miles to fully set monitors.

Watch out for:

• Disconnecting the battery clears active codes but resets all readiness monitors to 'Not Ready', guaranteeing an emissions test failure.
• The 'Permanent DTC' cannot be erased with a scan tool; it disappears after the car's computer verifies the repair via a drive cycle.
• Failing to meet specific drive cycle criteria (like fuel level) prevents the monitor from running.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An active P2404 code is an automatic failure. For model years 2010+, a 'Permanent DTC' must be cleared by a proper drive cycle before passing.
• New York: A vehicle fails the NYS inspection if the Check Engine Light is on for any emissions code. Readiness monitors must be set before re-inspection.
• Texas: An illuminated Check Engine Light results in an automatic failure. Clearing codes right before the test results in a rejection for 'Not Ready' monitors.

Most Commonly Affected Vehicles

• Subaru Outback (2015-2023) — Extremely common issue caused by overly sensitive ECM software. Requires an update per TSBs like #09-122-24R.
• Subaru Forester (2017-2023) — Frequently caused by a software glitch requiring an ECM reprogram per TSB #09-122-24R. If software is current, the pump is the next failure point.
• Subaru Impreza / Crosstrek (2017-2024) — Known software issue addressed by TSBs #09-118-24R and #09-122-24R. The leak detection pump is a high-failure part if software is updated.
• Subaru WRX / STI (2015-2022) — A software update per TSB #09-131-25R is the most common fix. Condensation buildup inside the pump triggers the code.
• Subaru / Toyota BRZ / GR86 (2022-2024) — Notorious issue caused by overly sensitive ECM software. Fix requires a software update referencing Subaru TSB #09-128-24R.
• Volkswagen Jetta / Passat / Golf (2005-2016) — Frequently traced to a failing Engine Component Power Supply Relay (J757). Check this relay before replacing the pump.
• Audi A6 / A4 / A3 (2005-2012) — Often caused by a faulty J757 relay. The pump's internal solenoid resistance should measure around 16 Ohms.
• BMW X5 (E70) / 3-Series (E90) (2007-2013) — Known issue pointing to a failure of the Leak Diagnostic Pump (DMTL). The pump itself is the most common failure part.
• Hyundai Elantra / Sonata (2011-2017) — Indicates a failure of the leak detection pump assembly itself or a wiring issue near the pump connector.

Manufacturer-Specific Notes

• Subaru: The ECM software is overly sensitive to temporary pump seizure from condensation. The official repair requires a dealer software update (TSB #09-122-24R) before replacing parts. This code also disables the EyeSight system.
• Volkswagen / Audi: The leak detection pump (V144) is powered by the J757 Engine Component Power Supply Relay. This relay is a known failure point and causes P2404 even if the pump is perfect. Always check the relay first.
• Dodge / Chrysler / Jeep: These brands use an Evaporative System Integrity Monitor (ESIM). When installing a new one, it must be oriented correctly (connector at 3 o'clock) or it will set a fault code.
• BMW: BMW refers to the leak detection pump as the DMTL (Diagnostic Module for Tank Leakage). The pump itself is the most common failure point, located in the right rear wheel well.
• Subaru (Warranty): The ECM software update is covered under the Federal Emissions Defect Warranty (8 years/80,000 miles). For PZEV models in CARB states, the warranty extends to 15 years/150,000 miles.

Real Owner Stories

2023 Subaru Forester at 13K miles - The Software Fix

Check Engine Light illuminated two days after buying the car. The dealer initially tightened the gas cap and cleared the code, but it returned four days later.

What they tried:

1. Tightening the gas cap.
2. Dealer cleared the code without diagnosing the root cause.

Outcome: The actual fix was a dealership software update for the Engine Control Module (ECM) per a Technical Service Bulletin (TSB). This reprogram corrected the computer's over-sensitivity to the pump's operation in cold weather.

Lesson: On a modern Subaru, P2404 is almost always a software issue. Insist the dealer check for TSBs related to ECM updates before agreeing to parts replacement.

2018 VW GLI - The Overlooked Relay

Owner experienced a persistent P2404 code and replaced the leak detection pump based on internet advice.

What they tried:

1. Replaced the EVAP Leak Detection Pump with a new part.

Outcome: The Check Engine Light returned one day later. The actual cause was a faulty Engine Component Power Supply Relay (J757), which provides power to the pump. Replacing the $25 relay permanently fixed the issue.

Lesson: Don't assume the component named in the code is the root cause. On VW/Audi vehicles, test the J757 power supply relay before buying a new pump.

2013 Subaru Forester - The 'Top Off' Mistake

Owner triggered a P2404 code a few days after over-filling the fuel tank until gasoline splashed out.

What they tried:

1. Reset the ECU by disconnecting the battery.

Outcome: Habitually 'topping off' forced liquid gasoline into the charcoal canister, saturating it and flooding the leak detection pump. The repair required replacing both the saturated charcoal canister and the ruined pump.

Lesson: Never 'top off' your fuel tank after the pump automatically shuts off. Liquid fuel destroys EVAP components and leads to expensive repairs.

2024 Subaru Crosstrek - The Backorder Reality

A nearly new Crosstrek threw a P2404 code. The owner took it to the dealer for warranty service.

What they tried:

1. Dealer diagnosed a defective EVAP Leak Detection Pump (ELCM).

Outcome: The dealer confirmed the pump failed, but the part was on a nationwide backorder for months due to high failure rates. The owner had to drive with safety systems disabled while waiting for the part.

Lesson: Even with a correct diagnosis under warranty, supply chain issues for high-failure parts like the Subaru ELCM cause significant repair delays.

How to Prevent This Code From Triggering

• Avoid 'Topping Off' Your Fuel Tank (Every fill-up) — Overfilling forces liquid fuel into the vapor-only charcoal canister. This saturates the canister and damages the leak detection pump's internal motor.
• Inspect and Clean the LDP Air Filter (Every 30,000 miles) — A clogged air filter forces the pump motor to work harder, altering its electrical draw and leading to premature failure.
• Inspect Under-Vehicle Wiring (Annually (especially in Rust Belt regions)) — Catching early signs of corrosion on the connector pins prevents high resistance or open circuits that trigger P2404.
• Ensure Gas Cap is Tightened Correctly (Every fill-up) — A loose cap allows moisture-laden air into the EVAP system, promoting internal corrosion inside the leak detection pump.

Frequently Asked Questions

Can a loose gas cap cause a P2404 code?

No. A loose gas cap causes a physical leak code like P0457 or P0456. Code P2404 is strictly an electrical circuit performance problem with the leak detection pump itself.

I replaced the leak detection pump and the P2404 code came back. What now?

You likely misdiagnosed the root cause. The most common remaining culprits are outdated ECM software (especially on Subarus), a broken wire, or a bad power relay (on VW/Audi). Check for Technical Service Bulletins (TSBs) before replacing any more parts.

Is it safe to drive my car with a P2404 code?

Yes, driving with P2404 will not damage your engine or leave you stranded. However, your vehicle will fail an emissions test and pollute more. On many newer cars, safety features like automatic emergency braking remain disabled until you fix the code.

Why did my Subaru's EyeSight turn off with the check engine light?

Subaru programs its vehicles to disable advanced driver-assist systems like EyeSight whenever the check engine light illuminates for emissions faults. This is a default safety precaution. Fixing the P2404 code restores EyeSight functionality.

Should I use a smoke machine to find the problem for P2404?

No, skip the smoke machine. P2404 indicates an electrical fault, not a physical vapor leak. Using a smoke machine on sensitive systems like Subaru's can actually contaminate and ruin the leak detection pump.

What does 'Permanent DTC' mean when I scan for P2404?

A 'Permanent' code cannot be cleared by a scan tool or by disconnecting the battery. It only disappears after you fix the underlying problem and the car's computer successfully runs its own internal EVAP test. You must complete a specific drive cycle for the computer to verify the repair.

How much does it cost to fix code P2404?

A dealership software update costs $80-$200 but is often free under the 8-year/80,000-mile federal emissions warranty. Replacing the leak detection pump costs $200-$400 for parts and labor. A simple relay replacement on a VW or Audi costs under $100.

Will clearing the code with my scanner fix the problem?

No. Clearing the code only turns off the check engine light temporarily. The car's computer will run the EVAP test again, detect the electrical fault, and trigger the code again.

Key Takeaways

• Code P2404 indicates an electrical failure in the EVAP leak detection pump's feedback circuit, not a physical vapor leak.
• On 2015+ Subaru models, an overly sensitive ECM triggers this code; a dealership software update (TSB #09-122-24R) fixes it 90% of the time.
• Replacing the leak detection pump costs $200 to $400 total, but always test the $25 power supply relay first on VW and Audi vehicles.
• Driving with P2404 is safe for the engine, but it guarantees a failed emissions test and disables safety systems like Subaru EyeSight until repaired.