Depending on if you have a Cali Spec eclipse or a Fed. Spec eclipse, If you have a Federal Spec. you only have an oxygen sensor before the cat and right after the cat. and you won't have one in the header.
You can find them in the exhaust pipe. Depending on engine size you might have anywhere from 2 to 4 oxygen sensors.
Upstream Oxygen Sensor heater performance. That will be the first oxygen sensor in the exhaust pipe ( closest to the engine ) on the passenger side head. You need to check the wireing connector that hooks to the oxygen sensor for a broken wire are bad connection. If you find no problems, then replace oxygen sensor.
Have you check the manifold? There should be one at the manifold and one at the catalyc! Hope you find it!
Find your Sensor, un-screw it 7/8 the wrench usually. Un-hook the electrical cable. Screw in the new Sensor then hook up the electrical cable...
follow the exhaust vent from the engine, if it's anything like my 97 eclipse it should be a few feet from the bumper on the underside, not convenient but you should be able to reach it without blocks or a lift.
Its right on the exhaust manifold, if u look down from the top u should see the cable and be able to locate it. There is also a rear O2 sensor between the header and the catalytic converter.
Its on the side of the transmission right next to the oxygen sensor on the driver side near the front of the car
it should be the bank facing the front of the car in the manifold. you should be able to find it right in front when open the hood
The 1988 Toyota oxygen sensor is located on the air cleaner housing. You will find the sensor, on the back side of the housing.
The upstream heated oxygen sensor is located ahead of the catalytic converter The downstream heated oxygen sensor is located behind the converter
it has two that i can find
To diagnose a bad sensor you need to hook it up to a code reader to read the stored trouble codes. Most auto parts stores will do this for free and tell you what sensor is bad and where it is located.