P2401 Code: EVAP Leak Detection Pump Control Circuit Low
The leak detection pump's control wire reads too low – most often a wire rubbing through to ground.
At a glance
Severity: Low
- Meaning
- EVAP Leak Detection Pump Control Circuit Low
- System
- Emission Controls · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $30–$1,300
- DIY difficulty
- Moderate
The leak detection pump (LDP) is switched by the engine computer, which also watches the voltage on the pump's control wire in both the on and off states. P2401 means that voltage sits lower than the computer expects, which almost always points to the control side of the circuit touching ground somewhere between the pump and the computer, or to a pump winding that has partially shorted and pulls the line down. On vacuum-operated LDPs (older Chrysler, Dodge, Jeep and US-market VW) that wire feeds a small solenoid; on electric canister pump modules (Toyota, Lexus and others) it drives the pump motor. A grounded control wire can leave the pump or solenoid switched on whenever the key is on, and the EVAP leak test is suspended until the fault is gone.
Can I keep driving? Driving is fine and the engine isn't affected. If you hear the pump humming or clicking constantly with the key on, get the short found soon, because a pump that never switches off wears out quickly.
How to read P2401
- P Powertrain
- 2 Generic (SAE)
- 4 Auxiliary emission controls
- 01 Specific fault
Symptoms
- Check engine light with no change in how the car drives
- Leak detection pump buzzing, humming or clicking nonstop with the ignition on
- EVAP readiness monitor stuck at 'incomplete'
- In some cases a fuse for the EVAP or engine-control circuit blows
- Code resets within one drive cycle after clearing
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Control wire chafed through its insulation where it runs along the frame rail, tank strap or near an exhaust heat shield
- Solenoid coil or pump motor with shorted windings (resistance well below spec)
- Water or road salt inside the pump connector bridging the control pin to ground
- Harness pinched during tank, fuel pump, exhaust or hitch work
- Low battery or supply voltage during the test making the reading marginal
- Faulty output driver inside the engine computer
Diagnosis step by step
Check battery voltage first
Measure the battery with the engine off; it should read at least 12.4 V. A weak battery or charging problem can pull every monitored circuit low, so fix that before chasing the EVAP wiring.
Tools: Multimeter
Listen for a pump that never stops
Key on, engine off, and listen at the canister area near the fuel tank. A steady hum or rapid clicking that doesn't stop after a minute suggests the control line is grounded and the pump is being switched on constantly.
Tools: Flashlight
Unplug the pump and check the fault state
Disconnect the pump and clear codes. If the scan tool now shows an open-circuit code such as P2400 instead of P2401, the short is inside the pump; if P2401 returns with the pump unplugged, the short is in the wiring.
Tools: OBD-II scanner, Screwdriver
Test the control wire for a short to ground
Disconnect the battery, the pump plug and the engine computer connector. Measure resistance from the control wire to a clean chassis ground; a healthy wire reads open (OL). Any reading in ohms or low kilohms means a short, so flex the harness along the frame to find the spot.
Tools: Multimeter
Measure the pump winding
Compare the resistance across the pump's terminals with the service specification. A solenoid that should read in the tens of ohms but shows only a few ohms, or a motor winding with continuity to its metal housing, is internally shorted and needs replacing.
Tools: Multimeter
Repair, clear and let the monitor run
After repairing the wire or replacing the pump, clear the codes and confirm the pump runs only when commanded. The EVAP monitor typically needs a cold overnight soak and several drives with a fuel level between roughly a quarter and three quarters.
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 |
|---|---|---|
| Dry and seal the pump connector, replace corroded terminals | Yes | $30–$120 |
| Splice and re-route a chafed control wire, add protective loom | No | $120–$350 |
| Replace vacuum-type leak detection pump | Yes | $150–$400 |
| Replace electric canister pump module | No | $280–$700 |
| Repair or replace engine computer | No | $500–$1,300 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Toyota
On Toyota trucks and SUVs the canister pump module and its harness sit near the rear frame rail and fuel tank, exposed to spray and gravel. Pump codes on these vehicles are frequently traced to a wet connector or a harness rubbed against a bracket; the module itself is usually sold as one assembly.
Field data
| Toyota | 12 | Scion Xa, Corolla, Yaris Liftback |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
An OBD smog check fails with the check engine light on, and the EVAP monitor can't complete while P2401 is stored. After the fix, drive normally for several days so the monitor finishes before the retest.
Frequently asked questions
Why does 'circuit low' usually mean a wiring problem?
The computer expects a certain voltage on the control wire when the pump is off. The most common way for that voltage to collapse is the wire touching the car's metal body through worn insulation, which is why the harness gets checked before the pump.
Can a shorted pump damage the computer?
Modern engine computers protect their outputs and shut the driver off when they detect a fault, which is why the code sets. Repeated shorts over a long time can still weaken the driver, so it's better not to leave it.
Is P2401 the same as P2400?
They're siblings. P2400 means the circuit behaves as if it were open, P2401 means it's being pulled low. Unplugging the pump and seeing which code appears helps tell a wiring short from a pump fault.
Could the pump running all the time drain my battery?
On most vehicles the pump circuit loses power when the ignition is off, so it won't drain the battery while parked. With the key on for long periods, though, a constantly running pump will overheat and fail sooner.