Hi All, I got this check engine code about a month ago, thought that it may be the O2 sensor in the pre cat (as soon as you come off the exhaust headers) so I replaced it and had the computer reset. it came back on again about 2 weeks later. I bought a self scan tool to check it myself rather than pay for it every time. this is what I got:

P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)

This is the freeze frame data from the scan tool

Fuel Sys 1 CL
Fuel Sys 2 CL-Fault
Calc Load % 32.94
ECT (C) 94 (degrees celcius)
STFT B1 (%) -3.91
LTFT B1 (%) -14.84
Eng RPM 1583
Vehicle Speed (km/h) 52

98 Mazda Protoge 1.5L
166,786 km on the car
(Recently replaced - rotor button & Cap, Spark plugs & Wires, Air Filter, PCV Valve, Transmission fluid and filter, all fluids are at proper levels, oil is clean W/new filter)

So I think this is telling me that my Pre-Cat Converter is only working at 32% of it's total capacity??? and I would have to replace it? if anybody can give any insight it would be greatly appricated. everywhere I check they only have a universal pre cat, and most places don't even list one for the car, the dealer wants 1300 for just the pre-cat. thanks for any help

 

Looks like Walker makes a replacement,

http://www.walkerexhaust.com/catalog...uponScreen.asp

Also Eastern Catalytic
http://www.ecatalyticconverter.com/m...-2807-cat.html

Get a Mazda 1998 shop manual (not chilton or haynes) and check that exact code. My 1996 manaul doesn't list that code but does list P0420, which points to either the Heated oxygen sensor, or the warm up three way catalytic converter. There are number of things that can make the O2 sensor appear to fail, including the intake manifold vacuum, and the fuel line pressure. (these cars are really picky about having a clean fuel filter) Resistance across the Sensor at the center and left terminal, with the 2 prongs at the top of the plug, Should be approximately 6 ohms.

The 3-way cat is the one directly after the exhaust manifold.

If you have a Foreign Autopart in your area, they are really competitve on parts for these cars.

 

Thanks for the fast reply, I will go after the fuel filter, I've had the part for over a month now, and just haven't had time to change it. When you said about checking the resistance across the sensor, which one are you refering to? the first O2 sensor or the second? (the first is a 3 wire sensor, the second is a 4 wire sensor). In reference to the links you gave me, I checked them out, with the Walker site, it seems they only list a part number for the 'actual' cat converter. the part I am hunting for, is located around the area of of where it starts (Pre Cat converter) (16110) where it says "gasket NA", the part they list, 54333 is the 'actual cat converter' which is where the second O2 sensor is further down the exhaust. Like I said though I will change the fuel filter, and do a vacum check, and will hunt the parts stores for the pre cat, thanks again for your help.

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Yeah, Eastern Cat has that part listed. You should check both O2 sensors.