2004 wrangler chek engine light on. Code

The "gas cap light" actually does not mean the gas cap is loose or defective.It is telling you there is a leak in the fuel system somewhere,usually a vapor line or stuck or defective valve.Not very often is it the gas cap that causes the light to come on.Time for a scan and a smoke test to fine the leak.

Trouble Code: P0442

EVAP System Small Leak Detected

Possible Causes:


EVAP fuel tank or canister vapor hoses leaking or damagedEVAP system component leaking, damaged or has failedFuel tank cap is loose, or the cap release pressure is incorrectLeak detection pump damaged or leaking.Also check the fuel filter for leaks.Does canister have filter on bottom?

this is not just a bad gaas cap code. it is a leak code for the evap system and will need to be tested to find leak. look underneath vehicle and check hoses on the evap canister for cracks or fallen off the canister is next to tank rectangular box. if dont find anything it will need to be "smoke" tested to find the leak

Hello and welcome. this indicates a problem with the evap system, which a gas cap can be the problem, along with allot of more causes. could be a bad gas cap, vent sol. purge valve or one of the evap lines leaking. two things that need to be done to help find the problem. first thing, have the system scanned for trouble codes, the system will store trouble codes. this helps in isolating the problem. the second thing, is to have the fuel tank system smoke tested. this will will isolate the evap leak.

Best not to ignore the check engine light because it also can indicate a serious running problem just as it is indicating a pollution problem now. I don't trust folks that have 'snap' answers for a given problem without any kind of testing (the fuel cap). This problem can be caused by split vent hoses or fuel filler hose, sensors that leak or read incorrectly--the list goes on. Smoke generator tests can help track this down but require intelligent analysis to replace or repair the correct component. Finding someone like this to take the time to be at least fairly sure of a cure before loading the car up with unnecessary parts is a rare find. Good luck!

Same problem on my 2001 TJ. Replaced cap, passed smoke test, supposed pinched hose fixed etc; light kept coming back on usually right after a cold start every other week or so. Three months later after trip to dealer and $367, it was due to an intermittenent evap cannister purge solenoid.

buzzer can be a loose connection at emergency brake lever or brake switch above brake could be stuck.

sounds like you have a leak in EVAP system need to have tested to find leak they make a smoke machine to test

P0440 - Evaporative Emission (EVAP) System


evaporative emission (EVAP) system has a large leak.
Check the gas cap or vent valve. these are the most common problems.


The Powertrain Control Module (PCM) at different times performs various tests on the EVAP system. OBD II Enhanced EVAP systems are in place to keep fuel tank vapors from venting into the atmosphere, and instead purges them into the engine to be burned. Regular pressure tests are conducted by the PCM to monitor the sealed system for leaks. The PCM monitors the EVAP system pressure by watching the Fuel tank pressure sensor (FTP). When the sensor indicates a small leak in the EVAP system, this code is set.


Here are some additional causes.

* A small leak in any of the EVAP hoses or fuel tank hoses
* A small leak in the purge valve or vent valve
* The EVAP Canister may be leaking

Check engine light has **** to do with any of what you listed. It only relates to pressures and sensors. Retorque your throttle body, check resistance on your sensors and if that doesn't work change the map sensor. They're bad on these vehicles