lhpdiver

Hi,

Trying to get to the bottom of what is causing the check engine light on the dash. The light has been lit a long time. In the spring we had the code read (456). We had a fitting replaced and the code changed to (442). The light is on again. Are those error codes very closely related ?

Also - we just had a tune up (replaced spark plugs, cleaned injectors, replaced air filter and replaced evaporator hose). Since then the Jeep seems to hesitate in idle every 30 seconds or so, tach drops a little then comes back up. Mechanic says maybe a vacuum leak - never noticed this before tune-up. Could all this be somehow related ?

Thank you.

2kg4u

Usually this P0456 code is caused by an incorrect or faulty gas cap. Filling the fuel tank with the engine running could conceivable cause this code as well or if the cap wasn't properly tightened. Any of the following could also be the cause:

• 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

A code P0442 most likely means one or more of the following has happened:

• A loose or improperly affixed gas cap
• A non-conforming gas cap (i.e. not factory/original brand)
• A small leak/hole in a fuel vapor hose/tube
• Other small leak in EVAP system
• Faulty vent o-ring seal
• Defective vent valve
• Defective purge valve
• Defective leak detection pump

Yes, these codes are closely related.

lhpdiver

Regarding the gas cap - I failed to mention - brand new $30 USD gas cap purchased in the spring from Jeep dealer. Perhaps that caused the change in code ? Does anyone know - are all the codes captured or does the computer stop on the first code ? In other words - might I have always been getting a 456 AND a 442 code ? Can the computer be asked for ALL the codes it sees ?

CCKen

Asking the PCM for codes is a function of most scanners. You can select active codes (that put the CEL on) or pending codes that haven't gone active, yet.

It would help if you compelted your profile and described the Cherokee you have (year, engine, transmission, etc.)

lhpdiver

Still in Mexico - 2001 Jeep Cherokee Sport w/ 98K miles. Check engine light still coming on - but not as often - and really never when engine is warm. Brought the Jeep back to the mechanic mid-week. He said they replaced some hoses which might have had tiny cracks and maybe that would cause the 442 error code. (No charge for the visit). He said at this point you have a new gas cap, new evap hoses - the next thing to replace is the "electrical component of the evap system". Roughly $125 USD. Does anyone know what this part is properly called? Does what he is suggesting make sense ? Can anyone offer something else I can suggest to him ?

Thank you.

2kg4u

He is likely referring to the EVAP purge solenoid. The PCM uses the EVAP purge solenoid to control purging of excess fuel vapors stored in the EVAP canister. Do you have emissions testing requirements in Mexico? The issues you are seeing have no impact on driveability whatsoever. I am a stickler on having everything on my car work properly, but if you don't have emissions testing and you don't mind the CEL, you don't have to spend money on this.

BTW, you can buy a EVAP purge solenoid for your Jeep for aound $30 in the US.

lhpdiver

Thanks Roy,

Yes we have mandatory emissions testing every 6 months here. I failed hydrocarbons about a month ago but passed after a tune-up.

If this "small evap leak" were the only reason that light would come on I could live with it but I don't like ignoring the light and then find out something else was wrong. And - the light has been on so long I worry the bulb will blow and I won't know if something else goes wrong.

Is it so trivial to replace that solenoid that I should pick one up on ebay and do it myself ?