P2404 Code: EVAP Leak Detection Pump Sense Circuit Range/Performance
The switch that reports the leak pump's position isn't changing state the way it should during the test.
At a glance
Severity: Low
- Meaning
- EVAP Leak Detection Pump Sense Circuit Range/Performance
- System
- Emission Controls · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $20–$450
- DIY difficulty
- Moderate
Vacuum-driven leak detection pumps (Chrysler, Dodge and Jeep LDP, US-market VW) and Chrysler's later natural vacuum leak detection (NVLD) unit contain a small switch that tells the engine computer where the diaphragm is. During the leak test the computer cycles the pump and expects that switch to open and close at a believable rate. P2404 means the switch signal is present but doesn't make sense – it stays stuck in one state or changes too fast or too slowly. Unlike the P2400–P2402 circuit codes, this is usually a mechanical problem: no vacuum reaching the pump, a torn diaphragm, a blocked fresh-air filter or a reed switch that sticks.
Can I keep driving? Keep driving normally – there's no effect on the engine. Because a stuck switch can mask a real vapor leak, don't ignore a fuel smell while the code is present.
How to read P2404
- P Powertrain
- 2 Generic (SAE)
- 4 Auxiliary emission controls
- 04 Specific fault
Symptoms
- Check engine light, no driveability change
- EVAP monitor won't complete
- Code sometimes comes and goes with weather, worse in freezing or wet conditions
- Occasionally a faint whistle or hiss near the canister with the engine idling
- Leak codes such as P0455 or P0442 appearing alongside
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Reed switch or diaphragm inside the LDP/NVLD worn, torn or sticking
- Cracked, collapsed or disconnected vacuum supply hose to the pump (vacuum-driven LDP)
- Clogged fresh-air filter or vent hose – mud, dust, insects
- Water or ice inside the pump after driving through deep water or in winter
- Intermittent sense wire or loose connector pin
- Engine computer misreading the switch (rare)
Diagnosis step by step
Watch the switch status on a scan tool
Many scan tools show an 'LDP switch' or 'NVLD switch' status. With the engine idling, command the pump or solenoid on and off: the switch should toggle each time. A status that never changes points to the pump or its vacuum supply.
Tools: OBD-II scanner
Check vacuum at the pump
On vacuum-driven LDPs, pull the small supply hose at the pump and connect a vacuum gauge. At a warm idle you should see roughly 15 to 20 inHg; little or no vacuum means a cracked, split or plugged line between intake and pump.
Tools: Vacuum gauge
Inspect the fresh-air side
Find the filter or open vent hose on the pump and make sure air can pass freely. Mud, packed dust or an insect nest in the inlet stops the diaphragm from moving at the expected rate.
Tools: Flashlight
Bench-check the diaphragm and switch
With the pump removed, apply vacuum to its supply port with a hand pump: the diaphragm should hold vacuum without bleeding down, and an ohmmeter across the switch pins should flip between open and closed as the diaphragm moves.
Tools: Vacuum gauge, Multimeter
Wiggle-test the sense wire
With the switch status displayed live, flex the harness at the pump and along the frame. A status that flickers while you move the wire points to a loose pin or broken strand rather than a bad pump.
Tools: OBD-II scanner, Multimeter
Retest the EVAP system
After the repair, clear the code and let the vehicle complete a cold soak and a few drives. If a genuine leak was hiding behind the stuck switch, it will now be reported as a leak code.
Tools: OBD-II scanner
Where the parts are
- 1Gas cap
- 2Charcoal canister
- 3Purge valve
- 4Vent valve
- 5Fuel pump
- 6Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace cracked vacuum supply hose | Yes | $20–$120 |
| Clean or replace LDP fresh-air filter | Yes | $20–$90 |
| Repair loose sense wire or connector pin | No | $80–$250 |
| Replace leak detection pump or NVLD assembly | Yes | $160–$450 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Jeep
Jeep, Dodge and Chrysler vehicles with the vacuum-operated LDP rely on a thin rubber supply hose from the intake. When that hose hardens and splits, the diaphragm can't move and P2404-type performance faults follow, so check it before condemning the pump.
Emissions / smog test impact
Will fail
With the check engine light on, P2404 fails an OBD-based smog check. Because the switch fault can hide a real leak, expect the EVAP monitor to need several days of driving after the repair.
Frequently asked questions
What does the switch in the leak detection pump do?
It reports the diaphragm's position. The computer times how quickly the diaphragm moves between strokes; a slow rate means a tight system, a fast rate means a leak. If the switch doesn't respond believably, that timing can't be measured.
Could a cracked vacuum hose really set this code?
Yes. The vacuum-type pump needs engine vacuum to move its diaphragm. With a split hose the diaphragm barely moves, so the switch never changes state and the computer flags a performance fault.
Why does P2404 show up more in winter?
Moisture can get into the pump and freeze, holding the diaphragm or switch in one position. Once it thaws the code may disappear for a while, which makes the fault look intermittent.
My pump is new – why is the code back?
A new pump won't help if the supply hose, fresh-air filter or sense wire is the real problem. Check vacuum at the pump and the switch status on a scan tool before buying a second pump.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- US EPA – On-Board Diagnostics (OBD) program
- Manufacturer public service information (cross-checked)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy