Check engine light only comes on when I press the gas in my 1991 Toyota Preiva,changed the O2 sensors and it's still on

An engine emissions componenet may be out of range or failed like a temp sensor or oxygen sensor if there is no change in engine operation other than increased fuel usage and less pep..

Two additional items causing the engine light to come on include bad O2 sensor and bad Exhaust Gass Regulator (ERG) valve. Good luck

Sounds like your O2 sensor is malfunctioning. When the check engine light comes on, the computer goes into a preset mode bypassing the O2 sensor and that's why it suddenly runs good. Have the O2 sensor checked. You can also have the trouble codes read and they should point you in the same direction.

YES!!, you had it tuned, it runs good, but gas mileage dropped, and check engine light is on,it sounds like the o2 sensors are slow or even dead, i would replace them for sure and that just might solve all your problems,good luck, hope this helps.

The o2 sensor could very well cause the code to come up, as well as the milage issue. As that sensors job is to monitor the fuel/air mix.
But the gas cap is only one part of the evap system,you have the canister assy. lines the pcv valve etc.These systems will be checked for the
inspection anyway. Hope this helps. Good luck

if the converter was bad the engine would loose power . alot of times the check engine light will come on for the emmitions check youre gas cap some vehicles will send a signal to the computer if the co is not right and by changing the gas cap solved the problem .

check throttle cabe and tighten it a bit more to give it gas or also check your o2 sensors

Just trowing some suggestions out there, but, I would check the idle air control valve (solenoid) or the throttle position sensor. If they check out then my last guess would be the map sensor or the vaccuum to the map sensor. Hope I was able to help. Best wishes.

The P0141 code points to the O2 sensor heater circuit. It could be that there is a short in the wiring to the O2 sensor or it could be that the O2 sensor heating element itself is bad. The code is for O2 sensor Bank 1 Sensor 2. Bank 1 means its the O2 sensor connected to the exhaust pipe that runs to cylinder #1. Sensor 2 means that it is likely the O2 sensor after the catalytic converter on the same exhaust pipe.

Hi Phares,

There are quote a few sensors located all over the fuel, intake, engine, and exhaust systems. Any one of them can cause the Check Engine Light to come on.

A ew common problems that are worth checking:

Make sure the gas cap is tightened 3 clicks. Improper fuel tank pressure can cause the CE light.

Dirty fuel injectors, even though it runs good. Try a bottle of fuel injector cleaner run through a tank of gas.

O2 sensors could be going out early. Normally they need replacement at around 60K miles.

You can reset the light by pulling the EFI fuse under the hood, and reinserting it. (this is basically resetting the ECU, same as unhooking the battery, without having to reset all the other stuff like your radio buttons, alarm system, etc.) If you have an automatic transmission, your ECU will have to start over relearning your driving habits so your gas mileage may suffer for a month or so. But the CE light may stay off. If the light comes back on, you need to have it diagnosed by someone with a Toyota code reader.

Best of luck,
Eitan.