What COULD be the cause, and how do I determine the cause.. for the CHECK ENGINE LIGHT?!?!?! Totally hoping that I can soon drive it without having issues!

 

Possibly O2 sensor/s. Start with the upstream O2 sensor. They go bad first, and can cause the CEL (Check Engine Light).

 

I think if you cycle the key from on to off 3 times (ending on on) it should display the code in the odometer window. Otherwise you can take it to your local auto parts store and they can check the codes for you for free.

 

So, I cycled the ignition, got a P 0442 code which means fuel cap, so I took it off and put it back on, but the light hasn't gone off. Do I have to do something special to get the light off?

 

I think you'll have to drive it some to make it go out, unless the cap actually has gone bad and isn't sealing properly. Your other options are have the auto parts store clear the code, or take off both battery cables a hold the key in the start position for 30 seconds(I may be off on the time) to reset the computer.

 

30 seconds is correct but you only need to remove the negative terminal.

 

I would just replace the gas cap, there only $10 bucks at walmart. If it is throwing a code on the truck you won't pass a PA gas cap test, unless the mechanic does not use your cap

 

If your going to spend $10 on a gas cap you might as well just get a Diagnostic scan tool off amazon instead so you can view and clear your own codes. The Autel MaxiScan MS300 is like $20 plus shipping. Its cheap, but it does the job well and I can confirm this because I have owned one for a while and used it to help out a few people with no problems as of yet. It allows your to read and clear codes and it will pay for itself in no time!

 

A gas cap could be the problem, but there are some other problems that could make the light come on. Such as a LDP pump, purge solenoid or broken evap hose. Here is some information on the P0442 code.

Symptom List:
P0442-EVAP LEAK MONITOR MEDIUM (0.040) LEAK DETECTED
P0455-EVAP LEAK MONITOR LARGE LEAK DETECTED
P0456-EVAP LEAK MONITOR SMALL (.020) LEAK DETECTED
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P0442-EVAP LEAK MONITOR
MEDIUM (0.040) LEAK DETECTED.
When Monitored and Set Condition:
P0442-EVAP LEAK MONITOR MEDIUM (0.040) LEAK DETECTED
When Monitored: Immediately after a cold start, with battery/ambient temperature
between 40° F and 90° F and coolant temperature within 10° F of battery/ambient.
Set Condition: If there is a leak larger than 0.0409 and smaller than 0.0809 in the
evaporative system.
P0455-EVAP LEAK MONITOR LARGE LEAK DETECTED
When Monitored: Immediately after a cold start, with battery/ambient temperature
between 40° F and 90° F and coolant temperature within 10° F of battery/ambient.
Set Condition: There is a leak larger than 0.0809 in the evaporative system.
P0456-EVAP LEAK MONITOR SMALL (.020) LEAK DETECTED
When Monitored: Immediately after a cold start, with battery/ambient temperature
between 40° F and 90° F and coolant temperature within 10° F of battery/ambient.
Set Condition: There is a leak larger than 0.0209 and smaller than 0.0409 in the
evaporative system.
POSSIBLE CAUSES
LEAK AT GAS CAP
VEHICLE HISTORY AND SERVICE BULLETIN INVESTIGATION
VISUAL AND PHYSICAL INSPECTION
VERIFY EVAPORATIVE EMISSION SYSTEM LEAK
EVAP PURGE SOLENOID OPERATION
INTERMITTENT LDP MONITOR FAILURE
EVAPORATIVE EMISSION LEAK DETECTION
GAS CAP
LDP COMPONENT LEAK

 

I am gonna go with this one. I had replaced the Purge Solenoid with the expectation of needing to replace the entire EVAP system. I had a HORRIBLE Vacuum leak that a deaf man could hear. Once I replaced the Solenoid, the leaks seemed to have been solved. Now, there was ONE hose I had to replace, it was breaking at the connection. Before the light came on, I could have sworn that I heard a faint leak.... huh, gonna assume I am right.