My trusty friend ('99 XJ) is nearly 12 years old with 165K and he lit-up the CEL this morning when I drove it cold (35F). He didn't get any warm-up because I had to move him quickly to clear the garage door so wifey could am-scray (late start as is typical on first Monday after "springing ahead"). He told the scanner that he had a DTC of P0442 (Evap Leak Monitor Medium Leak Detected). I cleared the code and plan to monitor for a repeat since this is his first DTC for the Evap system. Can I get a little advice from the collective of Jeepdom regarding the most likely/common/typical component in the Evap system to fail first? Would you rate this kind of DTC as critical or just a nuisance?

 

Evap system code definitly falls into the nuisance catagory. Something as simple as an improperly seated gas cap, of any one of ten or more vapor hoses (most of which are on top of the tank) could have failed. Sadly, the CEL is the only way the computer can let you know of a problem. So if it's on because of an EVAP code, then it can't tell you if something else goes wrong. But.... an EVAP failure wont leave you stranded somewhere.

 

First thing to suspect would be the gas cap; especially if it is the original. Because there are a lot of "crap" caps out there, this is one thing I buy from the dealer.

If the cap checks out, be sure to check all hoses around the charcoal evaporative canister and the evaporative solenoid. Vacuum hoses get bad and that is where leaks can start.

If you really get stuck, a shop can perform a "smoke test", where smoke is introduced into the evaporative system and where it leaks out is where the fail is.

But check cap and hoses and such first.

 

Thanks youze guyz! I uncorked the gas tank for an hour and will take it for a ride this afternoon. Let's see if that CEL re-appears and if it does then I think I'll know how to approach it now - thanks to you.