I have a 01 toy echo 1.5 liter. trying to replace the rear o2 sensor but i cant see where the wire goes. the wire to it appears to go up thru the floor between the frt seats. is the plugin under there? or does it run all the way to the engine? thanks for your help.

The upstream Heated Oxygen sensor is said to be in good working condition if its voltage goes from low to high (100 mv - 900 mv) and vice versa in one to three times in a second.

the p0421 code on this vehicle is either caused by a bad catalytic converter or an oxygen sensor. your mechanic has a scan tool that he can verify if the converter is faulty by comparing the rear o2 sensor to the front sensor. If the rear o2 sensor's voltage is switching from rich to lean (01-1.0v) similar to the front's, then, it's a bad converter. The rear o2 sensor should keep a steady voltage reading. Have him do this test while at cruising speeds. good luck

0xygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
its a heated sensor an the heat is dead or too slow,
the ECU monitors this sensor and can tell if the heater is bad 2 ways.
its bad or the wires to it are bad.(burnt, etc)

420s is lazy cat, ignore this, because the front sensor is bad
the rear is hopeless case. fix 135s, reset all codes, and drive.

the code P0137 is low voltage o2 sensor bank 1 sensor 2.. mean o2 sensor rear of catalyst converter has low voltage it should stay around .500mv mean converter cat.do is job.with a voltmeter test backprobe signal when engine running. by default key on engine stop around .500mv.

These codes, po 138 bank 1 sensor 2 shorted to voltage and code po158 means bank 2 sensor two shorted to voltage. these are the two rear oxygen sensors in the exhaust system. there two up frt and two in the rear, check the wiring on the two rear sensors, make sure that the wiring is not cut or stuck between metal. if the wiring is good then replace both rear sensors, when you get them ask for the left and right after the cat sensors. or bk1 s2 and bk2s2. after replacing them reset the computer. go to an auto parts sotre or if you have a code reader you can do it. hope this helps good day.

It's an o2 sensor code. So you more than likley have burnt wires associated with that o2 sensor.
P1133 = O2 Sensor Fault - Insufficient activity (Bank 1 , Sensor 1)You remove the negative battery connection from the negative battery terminal for 10 minutes.

You ALWAYS reset your computer when you do sensor swaps, when fixed erase code, and see if it stays out. your pcm is getting the wrong info from sensor. good-day !

code #0406 = egr position sensor circuit high ( stuck egr valve or bad egr sensor most likely sensor )

code #2096 = downstream fuel trim system lean ( see next code )

code #0137 = O2 sensor bank 1 sensor 2 circuit low ( replace rear O2 sensor driver side )

code #2299 = brake peddle position/accelerator pedal position incompatible. ( hav you been power braking this truck? ) ( brake light was on wile accelerator was being pushed )

take off the tire remove the brake drum let go the four bolts on the inside part behind backing plate should be able to tap the whole unit out without taking off the brake pads

P1135=Air-Fuel Sensor Heater Circuit Response Malfunction,
This code does not identify a particular o2 sensor,
did you get a code that showed a fault leading to the one you replaced?
Have you checked the voltage in the other o2 sensors to compare.

code # 1150 is the air/fuel sensor,its like the o2 sensor. replace the sensor on the rear exhaust manifold on top and that will solve your problem, hope this is helpful.