My problems started with a P1173 CEL which has mysteriously gone away and has turned into a CEL P0421 and P0431 which points to the cats about every 100 miles between erasing codes. The car seems to run ok. Could the problem be that the car has the cheap bousch universal #15730 or even in need of a tune up? The car is getting 20 mpg and the light seems to come on after a slight lack of power when getting up to highway speeds This could also be my imagination! I also posted information under Code P1173. Any help would be greatly appreciated. Im also looking for a good deal on Struts.

 

My first question is there 2 O2 sensors per bank which equals 4 instead of 3? Second is why doesnt the P1173 code come on now? And the mechanic was not with a mazda dealer and I just purchased the car about a month ago. The car does have a 148,000 on it but it runs good and is in good shape, and its gonna be disappointing to find out that I have to replace the cats when Im used to driving my Toyota with 220,000 miles on it without any problems. But I would like to fix it regardless. I dont quite understand all the terms u sent me other than the problem is with both banks and it dont have a driveability problem. I would like to investigate the O2 sensors more, and possibly try what you are saying with the voltage, but I just have a cheap $20 dollar meter. thanks for getting back with me!

 

From: babyhuey
To: 2000smazda
Date: 7/14/2006 8:51:42 PM
Subject: RE: help

Who knows why the P1173 is not coming back. May have just been a computer glitch that worked itself out. If happens. There are a total of 4 oxygen sensors on the engine. Two in each cylinder bank. The ones in the exhaust manifold are give rich/lean feedback to the engine computer. The two further down in the exhaust are the ones that are used in the catalyst monitor testing. That is their only purpose in life on your engine. The signal voltge from those two sensors is what you want to watch. $20 meter will work fine as long as it can measure millivolts which sound like it can The wire you want to tap into for the left or radiator side bank is Green. The right bank, closest to windshield, is the White wire. Once you have tapped into one of the wires then get it set to measure millivolt scale. With engine fully warmed up raise the RPM to 2500 for around 3 minutes. This is to get the cat converter at operating temperature. the voltage should be fluctuating rather quickly back and forth between 100 and 900 millivolts. Now let RPM come back to an idle. Voltage should raise to up above 600 millivolts at least and remain somewhat steady for at least a full minute. You should not see it fluctuating anymore accross the mid voltage line of 450 millivolts. If it does continue to cycle back and forth from rich to lean then the converter is either bad or the aftermarket O2 is overly sensitive as the TSB I sent talks about.
Keep in mind that voltage below 450mv is lean exhaust and above 450mv is rich exhaust. The sensor is measuring the amount of free oxygen in the exhaust gasses. The reason that you want to see above 600mv or steady rich is this. The converter cleans up the exhaust gasses by combining those free oxygen molecules with bad Hydrocarbons and carbon monoxide molecules to make cleaner exhaust. If the rear oxygen sensor is not showing a fairly steady rich mixture it means that the converter is no longer using those oxygen molecules and has worn out. Hope that all makes sense. Not very good at explaining technical stuff clearly or so the wire says. If not then give a note back with any questions and will answer as best as I can.

 

From: babyhuey
To: 2000smazda
Date: 7/12/2006 5:15:47 PM
Subject: RE: help

Car would run fine setting those types of codes. Nothing wrong with engine operation but only that the rear O2 sensors have an excessive number of inversions or rich/lean switches at an idle when fully warmed up which would typically be caused by fron warm-up cat converters getting weak. What kind of mileage does the 2000 S model have. Coverters are covered for 8years or 80K miles under emissions warranty. I would be a little concerned about the use of universal sensors downstream of the Converters. Mazda has an older TSB that talks about overly sensitive downstream O2 sensors causing those codes to be set. The dealer that installed these universal sensors should have know better if they were a Mazda dealer. It has been out since 2001. The TSB is 01-003/01. Will try to send along the context of the TSB for you to read. I might be tempted to install these sensors first although by experience the fix does not work on higher mileage cars. Below 20-30k yes. Above that is a crapshoot.

TSB: 01-003/01
MIL ON - DTCS P0420 P0421, P0430 P0431
APPLICABLE MODEL(S)/VINS
All 1997-2000 Millenia S.

DESCRIPTION
Some vehicles may exhibit MIL illumination with DTC(s) P0420/0421 or P0430/0431 stored in memory with no driveability concerns present. This condition may be caused by an overly sensitive rear oxygen sensor(s), which falsely indicates an emissions concern and a DTC to be stored.

Customers having this concern should have their vehicle repaired using the following procedure.

REPAIR PROCEDURE
1. Verify customer concern.
2. Confirm FFD and stored DTC(s).
If DTCs P0420/0421 or P0430/0431 are indicated, proceed to STEP 4.

If any DTCs are indicated other than P0420/0421 or P0430/0431, perform the appropriate repair for those DTC(s) according to the appropriate troubleshooting section of the Workshop Manual and proceed to STEP 3.

3. Reconfirm FFD and stored DTC(s).
If DTCs P0420/0421 or P0430/0431 are now present, proceed to STEP 4.

If no DTC(s) are present, return vehicle to customer.

4. Replace rear O2 sensor only on the side that the MIL and DTC indicates. Refer to EXHAUST SYSTEM REMOVAL/INSTALLATION [KJ] in the Workshop Manual section 01-15B.
NOTE:

DO NOT replace both left and right side O2 sensors at the same time unless stored DTC(s) indicate both sides have concern.

DTC(s) P0420/0421 indicates right side O2 sensor. DTC(s) P0430/0431 indicates left side (closest to radiator) O2 sensor.


5. Confirm the switching ratio of the W-U TWC is greater than 2 to 1, by using the NGS tester and monitoring according to 2000 Workshop Manual section 01-16B.
If inversion ratio is greater than 2 to 1, repair is completed, proceed to STEP 7.

If inversion ratio is less than 2 to 1, proceed to STEP 6.

6. Replace W-U TWC according to EXHAUST SYSTEM REMOVAL/INSTALLATION KJ in the Workshop Manual section 01-15B.
7. Verify repair.
PART(S) INFORMATION


Part Number
Description
Qty.
Notes

KJY1-18-861
Rear O2 Sensor
1
Left Bank

KJY2-18-861
Rear O2 Sensor
1
Right Bank