2011–2018 Ram 1500: Check gas cap light or check engine light (EVAP leak detection ESIM, purge valve or cap)

Symptom: A gas-cap warning symbol or "check gas cap" message, then a check-engine light with P0456 or P0457, sometimes with P0440 or P0441.

Likely causes

1. Fuel cap. A RamForum member with a 2013 Ram fixed a recurring message by putting a thin film of grease on the cap's O-ring. Others found a new cap didn't help.
2. ESIM. A 2015 5.7L owner at 140,000 miles had P0456, P0457, P0440 and P0441. A new cap didn't fix it, but a new ESIM on the canister near the tank did, and he reported no codes 35,000 miles later. Members point out the ESIM is a vacuum switch, not a solenoid, so it won't click when you apply 12 volts. One owner's brand-new replacement ESIM turned out to be faulty too.
3. Purge valve. Another owner replaced the purge valve and PCV valve after a cap didn't fix it and had no codes since.
4. Wiring and installation. ALLDATA describes a 2014 Ram 1500 with P0456 and no smoke-test leak where the ESIM never read closed. The cause was a crushed signal wire near the driver-side exhaust manifold. Another ALLDATA case found an ESIM installed in the wrong position. Its connector must sit at 3 o'clock.

DIY or shop?

Cap, ESIM and purge valve swaps are DIY. Wiring and smoke tests are a shop job.

Useful steps

1. Inspect the cap seal and try a known-good cap.
2. Have a scan tool check whether the ESIM switch ever reads closed.
3. Test the purge valve for leaking through.
4. If parts don't fix it, have the ESIM wiring and the EVAP system smoke-tested.
5. Stop filling at the first click. Several owners stopped topping off.

Vehicle focus: 2011–2018 Ram 1500.

Safety / mechanic note

An EVAP fault usually isn't a safety problem, but a strong raw-fuel smell is. Get that checked right away. Verify with a mechanic before replacing parts.