CEL Code P0140 after non-fouler

[rpbrant]

Hello, this is my first post, so bear with me. I have a 2003 Protege5 with a cold air intake and a header installed by the previous owner.

I believe it also has a mil eliminator setup (electrical components spliced in). It has had a CEL light for almost two years which wasn't a problem until I moved to NJ where they test the ECU for emissions codes.

Yesterday I finally installed the cheap non-fouler solution found here that uses two adapters screwed togther that the sensor screws into.

After about 50 miles, the CEL came on again and the code is P0140.

Since the code indicates "no O2 activity", my question is whether a combination of the non-fouler and mil eliminator could be the problem.

Also if there are any other thoughts out there I'd appreciate any input.

Thanks.

 

[CheeseHelmet]

my question is whether a combination of the non-fouler and mil eliminator could be the problem

I believe so. The way an O2 sensor works is by generating a voltage based on the amount of oxygen is in the exhaust. A high-voltage indicates low oxygen and a low voltage indicates high oxygen. By the time the exhaust gases get to the second O2 sensor the air/fuel ratio should be leaner than before the catalytic converter. Without a catalytic converter the ECU sees higher voltages than it would expect from the O2 sensor so it will trip the MIL to indicate that something is wrong with your cat.

If you remove the catalytic converter, the idea is to make sure that the voltages getting to the ECU from the second O2 sensor are lower than what they actually are to mimic the presence of the cat. IIRC one of the popular MIL eliminator tricks is to put a resistor in series with the O2 sensor's output line. This lowers the voltage but can be unreliable. The non-fouler method achieves the same goal but by letting less exhaust reach the O2 sensor.

If you're using both of these techniques at the same time there's a good chance that whatever voltage is getting to the ECU is so low that it's guessing that your O2 sensor is dead. You should follow the wiring up from the second O2 sensor and cut out whatever "mil eliminator" was installed.

 

[rpbrant]

Thanks for the prompt reply. Your response is along the lines of what I was thinking. My next question then is if anyone knows how to "wire around" this.

Right now the two wires (white and blue) from the sensor run through a connect then get spliced into the two mil eliminator inputs (white and black). There is one wire out (red) which runs through a (aftermarket?) fuse into a connector on the fuse block.

I'm assuming the red wire is normally connected in stock configuration but how would I go from the two sensor wires to the one "red" wire?

If I had a wiring diagram I could figure it out but so far I haven't had a lot of success finding a manual for this car.

Thanks in advance for any help,

 

[CheeseHelmet]

Your bottom O2 sensor should have 4 wires, and I think the colors are: blue (signal), white (ground), black (heater), black (heater).

The red wire you speak of might be there to simply power the MIL eliminator. So if you cut out the MIL eliminator you should just be able to match the colors and be done with it. The red wire should be removed altogether. If you could take a picture of the wiring I could confirm this for you just to be safe.

If you'd like the wiring diagrams, you can get the whole book here: http://www.floptical.net/mazda/wire/P5_WIRE.PDF

See the following for more info: http://www.mazdas247.com/forum/showthread.php?t=123744855

 

[rpbrant]

Thanks for you help. Based on your info I've got a plan now that should allow me to to fix this.

BTW, I did download the schematic for future ref. There's also a service manual at the same site. Even though it's for a 2002, it's at least a start. I'll figure out the differences over time.

As for the red wire, I guess I should have figured that out.

Thanks again.

 

[CheeseHelmet]

Cool, let us know how it goes!

 

[P-Funk!]

Uhm, huh?

The MIL eliminator 'wired in' is a resistor and a capacitor (only). No power to fuse needed. I would restore the all the wires to stock (just splice in new wire around whatever the PO did)...

 

[CheeseHelmet]

Uhm, huh?

The MIL eliminator 'wired in' is a resistor and a capacitor (only). No power to fuse needed. I would restore the all the wires to stock (just splice in new wire around whatever the PO did)...

There are some fancy ones which use a microcontroller to simulate how the O2 sensor is supposed to respond (something like this), I'm guessing he's got one of those. Pics would be nice

 

[P-Funk!]

huh!

Okay.