northtide

The check engine light comes on after fueling? Is this a serious problem? I just tuned-up the car, sent it to a trusted mechanic who said there is nothing wrong with it.

6SOARER

iTrader: (20)

is it pre 95 or 96 or later model? If its OBD2(96 or later), you may have a bad gas cap.. This will throw a EVAP code, check for any DTC's if any.

northtide

Its a 1993 sc400.I replaced the orginal gas cap with one with a key. Should I return to the original gas cap. When I bought the car, the fuel door was missing, thats why I bought a keyed gas cap.

6SOARER

iTrader: (20)

no, if its a pre 95 it shouldnt matter. Only the 96 or later models will set the CEL if your missing or have a bad gas cap. Next thing I would do is to pull the DTC's diagnostic trouble codes that is setting your check engine light off.

6SOARER

iTrader: (20)

Theres 2 ways to check for DTCs. Theres a DataLinkConnector in the engine bay and the other is located under the left side of instrument compartment.. I use the one in the engine bay cause its easier to access.

-Get a jumper wire or paper clip and jump E1 and TE1 together.
-To retreive code, turn ignition on but Do not start the car

The check engine light should blink. Count the number of flashes, if theres a 1.5-2.0 sec delay it maybe a 2 digit code. Example: If the light blinks 1-1 delay 1-1-1 then this is a 23 Code and so on..

Once you've pulled the code(s) this will give you an idea where to start troubleshooting.

Spooled

iTrader: (1)

Autozone will pull it for free w/o jumping pins.

When you fueled up, did you top it off and overfill the tank? Overfilling the tank will cause the evap system to pull raw fuel into the canister instead of vapors. this will throw some evap codes. But do the obvious checks, pop you hood and check for vacuum hoses loose, around the intake, etc.

But typically its the cap, just check the tension on the cap first, you can obviously tighten it, but how easy is it for the cap to be loosened? if it twists off with almost no effort, you need a new cap. It should take as much force to remove the cap as it did tightening it down. and always crank the cap down... its ok if it makes that racheting noise, give it over a ½ turn.

First things first though, get the codes pulled.