P0136 on 97' Mazda 626

Hi there,

Not long time ago, I fixed two codes (P0171 and P0421) on my on 97' Mazda 626. Problem was rather simple, I was searching for vacuum leak but it was caused by some idiot, who tampered with air mass flow meter, which was not faulty but one of the bottom screws was missing leaving about 8mm big hole, which caused leak, complete miscalculation of mixture, too lean system and choking when accelerator was pressed.

After I replaced that screw, everything went normal, check engine light went off and after 2 days I passed pennsylvania state inspection.

Engine was running smooth and fine. choking disappeared. But after 2-3 weeks, the check engine light went ON again. I said something I prefer no to repeat here , and decided that on weekend I'll go to autozone to do diagnostics. But before weekend came, after 2-3 days, the light went off by itself, without my interaction.

Now, it's in the state that it goes on and off every now and then, usually after 2-4 days. Without any particular reason, and without any visible problems for car or fuel efficiency. Gas mileage is OK, it makes about 28-30 mpg on freeway and 24-25 city, which is not bad for 10 years old car with 107k Miles.

I found that current code is P0136 which probably means (P0136--Oxygen Sensor Circuit Malfunction). If it is like that, why is comes and goes? why after 2-3 days? Due to humidity, weather, vibrations? If it is broken wiring, how can I found it, it would not show up if it will be in 'healthy' state, right?

change the o2! It would take longer to explain why it could be intermtitent
then to change it! at that mileage it's a good guess and should be done for amintenance if nothing else! It won't make it worse that's for sure!

Hi there,
I am trying to fix the problem, but I found it rather confusing. There are 2 major O2 sensor manufacturers, DENSO and BOSCH and plenty of retailers, with major ones like autozone. Each retail location says that my faulty sensor is different sensor, with completely different price from $60 to over $200. They also have different or missing connector. I even suspect that they do not have a clue. I would like to know for sure, which sensor should I replace.

So, where REALY are located the sensors in 97' 626 with automatic and 2.0L? Are there 2, both fairly visible from top, if you simply bend over the engine, and look between radiator and exhaust manifold?

Nothing like hidden somewhere under the car? Are they really close to each other, like only 10 inch apart on the exhaust manifold?

Do they have different conector, one male and one female? Which is the faulty one?

You know how to get the correct parts! Take your vin number to your local MAZDA dealer and order both of the sensors!

the code p0136 refers to bank 1 sensor 2
if you are looking under the hood it is the bottom sensor
your car has two sensors one before the catalitic converter and one after
to put it simply the one before runs the car
the one after checks to see if your catalitic converter is good

the two sensors have different plugs the difference is in the shape or how they are keyed
true your best bet is to go to mazda and order a downstream oxygen sensor
but if you choose to go to and auto parts store you still want a downstream oxygen sensor but you want a direct fit one with the plug already attached. the sensors with no plug are universal and require you to cut the old plug off and reatach it to the new sensor