14/08/2026 8:38 am
Topic starter
Automotive Q&A
Volvo S60 P0456 passes a cap test but fails the DMTL small-leak monitor
Review the evidence, add a focused answer, and distinguish confirmed measurements from assumptions.
Notifications
Clear all
Vehicle Questions
2
Posts
2
Users
0
Reactions
121
Views
0
A 2015 S60 repeatedly sets P0456. The cap seal and cap test are good. A smoke test with the DMTL valve in the commanded state shows no leak at the canister or hoses, but faint smoke eventually appears around the filler-neck connection behind the wheel liner. There is no visible crack.
Is the neck seal serviceable, and how should the source be confirmed before parts are ordered?
1 Answer
0
15/08/2026 9:49 am
Clean the connection and repeat the low-pressure test while viewing the neck-to-tank or neck-to-hose seal directly. Flex only as the service procedure permits. Confirm DMTL pump flow and valve operation with its guided test so a pump fault is not confused with a physical leak.
If smoke begins inside the connection and the neck is undamaged, use the VIN parts breakdown to identify the serviceable seal or hose. Do not add sealant to an EVAP joint; it can damage components and complicate future testing.
Topic starter
16/08/2026 8:54 am
The joint leaked at the filler-neck O-ring when the neck was moved slightly. The plastic neck and tank spigot were sound. A new specified seal held the calibrated leak test, and the DMTL monitor completed without P0456.