- Code
- P2420
- Applies To
- Most makes, generic code
- Loose Cap Can Set It
- Not named in our sources
- Typical Fix
- $210 to $251 at RepairPal
- The EVAP switching valve circuit voltage is high.
- A shop confirms it with the carmaker's EVAP test and a smoke machine before replacing parts.
- Usually yes for now, but get it fixed soon and check for open recalls.
What The Carmakers Call It
- EVAP System Switching Valve Control Circuit High, as printed by Subaru of America
Causes Named In Carmaker Bulletins
Our sources name the part this code points to but no single cause. Start with the Purge Valve guide.
No source ties this to the gas cap.
What The Fix Costs
The usual part for this code is the purge valve. Published estimates put it at $210 to $251 at RepairPal. The full table with every source and date is on the cost page. A diagnosis first keeps you from paying for a part you did not need, which is why we price what a check engine diagnostic costs before the fix.
Getting The Light To Go Off
After the repair the light goes off once the EVAP test runs and passes on three drive cycles in a row, and the code is erased after 40 warm up cycles, per CARB. The test only runs under set conditions such as a fuel level between about 15 and 85 percent, so it can take days.
Related Codes
Author Source EEAT Authors · Anthony's Author Page
Sources For This Page
- Service Bulletin 09-131-25, Diagnosis Procedures for DTCs P2404 and P0420 (March 4, 2025), Subaru of America, read 2026-11-12
- 13 CCR 1968.2, Malfunction and Diagnostic System Requirements, OBD II, California Air Resources Board (via Cornell LII), read 2026-11-12
- Purge Valve Replacement Cost Estimate, RepairPal, read 2026-11-12