P2420 Code: EVAP Switching Valve Control Circuit High
The switching valve in the EVAP canister pump module can't be switched – its control line stays high.
At a glance
Severity: Low
- Meaning
- EVAP Switching Valve Control Circuit High
- System
- Emission Controls · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $40–$1,400
- DIY difficulty
- Moderate
The switching valve sits inside the canister pump module used by Toyota, Lexus and other makers with an electric leak test. To run the test, the ECM energizes the valve so the small pump works against the fuel tank instead of a reference orifice. P2420 means the control line's voltage stays higher than it should when the ECM tries to do that. The usual reasons are a short between the control wire and a 12-volt feed, a coil that has shorted internally so the ECM's protected driver shuts down, or a poor ground at the module on designs that have one. Because the valve normally rests in its open, venting position, refueling is rarely affected – the main result is an EVAP monitor that never finishes.
Can I keep driving? No driving restrictions. The engine and fuel system work normally; plan the repair around your next emissions test.
How to read P2420
- P Powertrain
- 2 Generic (SAE)
- 4 Auxiliary emission controls
- 20 Specific fault
Symptoms
- Check engine light on, nothing else noticeable
- EVAP readiness never reaches 'complete'
- Refueling usually normal, unlike vent-valve-stuck-closed faults
- Pressure reading doesn't change when the switching valve is commanded during an active test
- Code returns immediately at key-on after clearing when the short is hard
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Switching valve coil shorted inside the canister pump module
- Control wire shorted to a 12-volt circuit in the rear harness
- Poor ground at the module or at a nearby body ground point
- Wet connector letting the power pin bleed onto the control pin
- Aftermarket wiring (hitch, alarm, remote start) tapped into the wrong circuit
- ECM driver circuit failure
Diagnosis step by step
Use the pressure sensor as a witness
Start the leak pump with the active test and note the pressure it pulls through the reference orifice, then command the switching valve on. On a healthy system the reading changes as the pump switches to the tank side; no change at all confirms the valve isn't moving.
Tools: OBD-II scanner
Back-probe the control wire
With the connector plugged in, back-probe the control pin and watch the voltage while commanding the valve on and off. On a typical ECM-grounded design it should drop close to 0 V when on; if it stays near battery voltage, the ECM isn't pulling it down or something is feeding it.
Tools: Multimeter
Check for stray voltage with everything unplugged
Disconnect the module and the ECM connector, key on, and measure the control wire to ground. Anything more than a fraction of a volt means the wire is touching a powered circuit.
Tools: Multimeter
Measure coil and module ground
Measure the valve coil resistance and compare it with the specification – a very low reading means a shorted coil. Also check the module's ground wire to the battery negative; a voltage drop above about 0.1 V with the pump running indicates a poor ground.
Tools: Multimeter
Replace the module only when the circuit tests good
If the harness, ground and power supply check out and the coil is shorted, replace the canister pump module. Clear the code and run the active test again before handing the car back.
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 |
|---|---|---|
| Repair or clean module ground point | Yes | $40–$150 |
| Repair control wire shorted to power | No | $120–$350 |
| Replace canister pump module | No | $250–$650 |
| Replace ECM (rare) | No | $600–$1,400 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Toyota
On Toyota and Lexus vehicles, P2419 and P2420 both refer to the switching valve inside the canister pump module. A scan tool with Toyota enhanced data lets you run the vent valve and pump tests separately, which helps separate a shorted valve from a wiring fault before the module is replaced.
Emissions / smog test impact
Will fail
P2420 keeps the check engine light on and the EVAP monitor incomplete, so an OBD-based emissions test fails. Once repaired, give the vehicle a few days of normal use with overnight cold soaks before retesting.
Frequently asked questions
Why can I still fill up normally with P2420?
The switching valve normally rests open, letting the tank breathe through the canister. With a 'circuit high' fault it usually just can't be switched closed for the test, so refueling isn't affected.
How is P2420 different from P2422?
P2420 is an electrical fault in the valve's control circuit. P2422 means the valve or vent path is mechanically stuck closed, which is what causes the classic slow-refueling and nozzle-clicking complaints.
Could a bad ground really cause a 'high' code?
On designs where the module has its own ground, a corroded ground connection can leave the control line floating up near supply voltage. Checking the ground takes minutes and is worth doing before replacing the module.
Do I need a dealer scan tool?
Not necessarily, but a tool that can run the EVAP active tests makes the diagnosis much faster. Without one you can still work through it with a multimeter and a wiring diagram.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy