2000 lexus gs300 emissions failed with no engine light on

no year, car, or model. stated?
nor engine option, , (strike 3)
and makes any answesr impossible
and there is no Emissions light, you named it wrong.
my wild guess is its the Check engine light or CEL or MIL
seen
here
http://dashboardsymbols.com/the-symbols/

if the CEL glows, get car scanned.
on cars with automatic transmissions, if it fails the same lamp glows.
cleaning it , is no trivial task.

Bad oxygen sensors in your exhaust depending on the type of car there can be between 4 and 8 oxygen sensors. They help tell them computer how the car is running and can adjust the richness or leaniness if the fuel mixture it is dumping into the cylinders

emission? you mean the SES or CEL? lamp ? check engine. or service engine,? lamp.
the car is under warranty for 8 years, take it in.
you could scan it with a scanner and if EVAP is failing
tighten the gas cap, reset the DTCs and lamp is now out.
and drive. top failure on all cars 1996 to now, is, loose gas cap.

if it has the brake lights as well for the ABS then i suspect a faulty computer ,end of story

Some luxury Models are equipped with standard emission lights. Try removing the battery cables for 20 mins of so with the vehicle off. Reconnect and start engine. Drive it for a little while. If the light is gonna come back on it will likely do it in under 10 miles. If it comes back on, have you car scanned for trouble codes.

When you turn the key 'on' the Check Engine Light is supposed to illuminate-that is also a check for the system-they probably removed the CEL bulb or the fuse for it-not good, and easy enough to verify-if so I would register a complaint to any state agency that regulates auto repair or emission stations. A disabled CEL will not in and of itself cause a failure in most states,but a code will-You will need to have the car scanned to see what the code is, and then come back on here with the actual code for help.

Toyotas and Lexus cars have some unique feaures. If your fuel cap is loose or the O2 sensors on the exhaust are faulty this results in an emission problem and the engine computer unit (ECU) engages the check engine light and disables the VSC (the VSC light comes on to warn you that it has been disabled). However you have p0500 code which says the car has no speed sensor signal. The seed sensor is located on the side of the final drive from the transmission and its job is to measure the speed of rotation of the output shaft. The ECU will compare the signals from this shaft along with the speed sensors in the wheel hubs. If there is a difference between these signals the VSC is engaged to apply braking effort to which ever wheel is slipping (running faster) than the other or that the transmission speed sensor would warrant.
So you either have an emission fault has fed back to the VSC and speed sensor missing (p0500) condition, or you have a faulty sped sensor which has tripped the VSC light and in turn the CEL.
Check your fuel filler cap is on tight, turn radio off and disconnect the negative lead to the battery for 5 minutes (this should clear the ECU memory of the code error). If p0500 error and CEL and VSC lights come back on then check the electrical connection to the speed sensor. Ensure it is clean and making a good contact, check the wiring for continuity. If everything else looks good consider changing the speed sensor.

really need more info on your durango ? millage , engine , other causes for poor emissions are weak motors , poor gas , tuneup problems and worn emission parts like lazy O2 sensors and catalytic converters

Sticking egr will raise everything except nox. Bad o2 bad cat hard to give an accurate diagnosis with out checking it

You can actually google this by putting lexus code ### for each one it will tell you what each one means