P0440, P0441, P0455 codes from gas cap, leak detection pump, purge valve, or cracked rubber lines. Smoke test isolates the leak.
The evaporative emissions (EVAP) system captures fuel tank vapors and routes them to the intake manifold for burning instead of venting to atmosphere. On the XJ, EVAP issues typically throw P0440 (general EVAP fault), P0441 (incorrect purge flow), P0442 (small leak), P0455 (large leak), P1494 (NVLD switch or leak detection pump - 1998+). Most common single cause: failed gas cap seal (replace before chasing more involved leaks; Stant 10832 about $10). Next common: cracked EVAP purge solenoid hose at the top of the intake manifold or the NVLD (natural vacuum leak detection) pump near the fuel tank. The NVLD pump on 1998+ has a small spring-loaded valve that fails closed and prevents the engine from drawing vapors. Smoke test the entire system (smoke into the gas filler with the cap loose) to find leaks visually. Charcoal canister in the engine bay can saturate from gasoline if you overfill - replace with Mopar 53034007.
| Part | Vendor | Est. price |
|---|---|---|
| Gas cap Stant | auto parts | ~$12 |
| EVAP purge solenoid | Mopar | ~$35 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.