The Leak Detection Pump In Your EVAP System

What The Sources Say About It

• Audi describes the leak detection pump as a vacuum driven diaphragm pump run by the engine computer. It needs the engine running and pressurizes the EVAP system, then watches for pressure loss over a set time. (source)

Other Leak Test Designs

• Natural vacuum leak detection. After shut off, the fuel tank makes a natural vacuum as the fuel cools. If the system cannot see that vacuum during its self test, it stores a leak code. Audi treats 2.5 mbar (0.04 psi) of vacuum as sealed. (source)
• Natural vacuum leak detection. Ford calls its version Engine Off Natural Vacuum (EONV). It uses the Ideal Gas Law, checks only for 0.020 inch leaks with the key off, and leaves 0.040 inch and larger leaks, including cap off, to the engine running test. (source)
• Natural vacuum leak detection. Hyundai found salt deposits inside the NVLD sensor on some 2016 to 2019 Sonata Hybrids could set P0456. (source)
• Chrysler ESIM. FCA documents place the ESIM on the clean air hose to the EVAP air filter. FCA says to replace only the ESIM detector if it is the bad part, not the canister. (source)
• Toyota canister pump module. The pump module bolts to the canister on the fresh air side. It holds the vent valve, pressure sensor, a 0.020 inch reference orifice and a vacuum pump, and is replaced as one unit. (source)
• Toyota canister pump module. The key off system first showed up on the 2004 Highlander, and by 2007 all Toyota models had it, per MOTOR. (source)
• Toyota canister pump module. Typical conditions for the key off leak check, engine off five hours, ignition off, coolant and intake air 40 to 95 F, altitude under 8,000 ft, battery 10.5 volts or more. The pump usually runs 5 to 10 minutes or less, and the driver can hear it. (source)
• Toyota canister pump module. If coolant is still above 95 F after five hours, the computer waits two more hours, then another two and a half. (source)

Codes That Point Here

What It Costs

Published estimates put a leak detection pump at $201 at YourMechanic. See every price row. For a real example of pricing the test before the part, see what a check engine diagnostic costs.

By Anthony Limpert, co-founder of Supercanic in San Jacinto, California, a shop with ASE certified mechanics. Updated November 12, 2026.

Author Source EEAT Authors · Anthony's Author Page

Sources For This Page

1. Technical Service Bulletin 2035519/1, P0456 or P0442, Q7 (October 23, 2013), Audi of America, read 2026-11-12
2. Technical Service Bulletin 2035073/1, P0456 NVLD very small leak (October 16, 2013), Audi of America, read 2026-11-12
3. 2009 MY OBD System Operation Summary for Hybrid Electric Vehicles (revised May 22, 2008), Ford Motor Company, read 2026-11-12
4. TSB 20-FL-003H, DTC P0456 EVAP very small leak, Sonata Hybrid (May 2020), Hyundai Motor America, read 2026-11-12
5. GPOP Issue Review 9100471, Vapor canister and ESIM (March 17, 2025), FCA US LLC, read 2026-11-12
6. Diagnosing Toyota's Key Off Evap System (February 2016), MOTOR Magazine, read 2026-11-12
7. Toyota key off evap system, Foreign Service (September 2006), MOTOR Magazine, read 2026-11-12
8. Leak Detection Pump Replacement Service and Cost, YourMechanic, read 2026-11-12