i have a 2000 millenia 2.5 automatic with 147000 miles. i have owned the car for 3 months. i got the check engine light after about 500 miles. i unplugged battery for 10 min and light shut off, it came on again after 100 or so miles so i pulled the battery again. it came on again today after approx 750 miles since last time. The car shudders and sits at about 300 rpm in drive sometimes then the cel comes on. if i shift to park it goes up to about 500 rpm and the shudder stops. i also have acceleration problems everyonce in a while. if i push the gas down harder it takes off after a second or so.So anyways i went to Orileys today and used their code puller and hooked it up. it came back with one code. it said "P1170 H02s11 Circuit too high or low Bank 1 sensor 1. what does this mean? the guy at orileys said his guess was a oxygen sensor, probably rear and it has to be ordered from the dealer. what should i do? Kennin i know your the expert so i figured you would have seen this code before and would know what to do. I am the one who had the squeal at start, you recomended changing the upper belt, i did and it worked perfect, no more squeal! so thanks for that.

 

1170 is the heated sensor, right bank. this would be the pre-cat sensor, on the bank closest to the firewall. since the code is erratic, it sounds like the sensor is dying. a new sensor should fix the problem. i dunno much about the 2.5, never owned one. looks like it only has 3 oxygen sensors, 2 pre-cat, and 1 post cat. it looks like bosch 13879, but i am not sure. from the description, which is kinda confusing, it is the rear sensor, in the pipe. NOT after the cat.

 

The PCM does not use rear O2 sensors for adjustments. Their only purpose is to monitor the efficiency of the converters. By comparing the o2 before the converter and after the converter it knows how well it is cleaning up unburned gases. Only the front o2 sensors before the converters is used by the PCM for adjustments to lean/rich switch.

 

if im looking at it right there are 4 o2 sensors, one directly by the radiator, one in the center of the engine near the fire wall in a pipe, and then if your standing at the driver fender theres one on a lower pipe that would be closer to you than the one near the firewall then theres one farther down that pipe after the cat. so would it be the one farthest and Highest (if that makes sense) away from you on the right? they all have 4 wire plug(white, white with grey stripe, grey and black)connecters. if i locate which one it is would it be ok to use a generic replacement rather than having to pay the dealer mark up?

 

Bank one is the firewall side, sensor 1 is the first o2 before the converter ( top)

 

what he said.

you can use a generic(universal) sensor. you will have to splice in the harness, i have done this several times. there is some confusion about aftermarket sensors, some people think that a sensor from the dealer is much better. i am sure mazda does NOT make it's own sensors, they contract out for them. probably denso. bosch also probably does NOT make this sensor, they buy it from the original manufacturer and rebox it. very common in the aftermarket.

 

I thought I submitted this allready so sorry if it shows up twice. At oxygensensors.com they list 4sensors for my engine. Precat center, precat front, precat rear, and postcat rear. So I assume precat center is the one by the radiator, precat front is the upper(farthest away from you if your at the driver fender) precat rear isvthe lower(closer to the driver fender and of course post cat is post cat. If this is correct I need the precat front? I just want to make sure before I order it. Thanks again

 

ok, again, i have no experience with a 2.5. on a 2.3, each exhaust manifold has a precat in it. so, each exhaust manifold will have 2 oxygen sensors on it, 1 before the precat, and 1 after. if your 2.5 has 4 sensors, then you would need the rear bank precat sensor. that's the best i can do, i have never even seen a 2.5 up close. i would think the 2.5, and most other engines, all have a precat on each exh manifold, but again, i dont know. and i am not confortable with giving out information that i have not personally done.

 

I own a 2001 Millenia that has a similar shuddering problem. Here are the details:

The car USUALLY fires up great and runs twenty or thirty minutes without any problems. Then as you are driving you feel the engine lose power, the tac drops down to about 1300 then the engine "catches" and everything is fine for a while. The longer you drive it, the shorter the time between power loses are. Usually the first one and the second one are separated by upwards to 10 minutes, the third is almost half that time, fourth 2-3 minutes and continues to decrease until you pull over half-crazied! The problem will continue again if you turn the car off and then back on. If the car has time to cool down it will begin from the start again. It has occasionally 1) skipped the slow spread out power loses and jump straight to violent shaking (almost as if you had taken your foot off the clutch to quickly, (this car is an automatic)) or 2) preformed its "trick" below 1300 RPM.

It seems to start the problem sooner on warm days and there have been a few cold days that it has never had any problems. In other posts drivers have described a similar problem related to their TCS and a couple vacuum lines, but my trusted mechanic doesn't like that idea and doesn't remember any vacuum issues last time he looked.

Mechanics have replaced: a selinoid, distributor cap, EGR valve

the most recent mechanic believes that for some reason, the computer is turning the injectors off causing the engine to lose power until it drops below 1300 RPM then the computer turns them on again.

I would GREATLY APPRECIATE ANY help. We have a long road trip on Friday Jan 31 and would love to get this fixed before then. Thanks a ton.

 

from your description, you have a 2.5. go to the other forum, mazdaworld.org, register, then post in the millenia section. you need someone like yel-low who is the resident 2.5 guru. and i think your "mechanics" are out in the deep end, and cant swim