P0421 check engine and O2 sensor problems

[cholland]

Ok, so i have a 2003 protege5 with 95k mi. on it. I have a header on it and used the non-fouler method so i wouldnt get a CEL for over a year with no problems.

Recently my lower O2 sensor came loose and got a dinged up and broke one of the wires which ended up giving me a P0140 code if i remember correctly.

So I went to schucks and bought two of the universal ones to replace both sensors at the same time. They have the same part number listed, 15733, for both the upstream and downstream sensors. After checking on autozone, they have the sensors but with different part numbers, 15733 and 15730.

After replacing both sensors now I am getting a P0421 code and am wondering if it because i used the same sensor for both the upstream and downstream sensor. I have no idea what to check next.

Any suggestions or input would be greatly appreciated because i hate seeing the glowing CEL in my dash!

 

[MS3_KIDD]

the p0421 code is Warm Up Catalyst Efficiency Below Threshold

sorry to tell you but universal o2 sensors are s***, they'll work for a little bit bit nothing beats a oem direct fit o2 sensor in the long run

if you have access to a scantool or digital oscilloscope, you'll want to watch your upstream and downstream o2 sensor voltage readings while in closed loop and look for the upstream to be switching steadly between 250mv to 850mv and the down stream should stay steady at about 450mv


double check your connections with the uni fit o2 sensors as the connectors they include (or any thing other than a direct fit plug) are questionable at best

id say you best bet to to get some oem sensors if you can and then continue diagnosis from there by rechecking voltage reading, performing a catalyst efficiency test etc

 

[Mike R]

a scope? a simple multimeter is all you need for the o2 voltages. ( I suggest a nice scantool though, they pay for themselves quickly)

I second the crap universal 02's, a freind of ine had the same codes with the cheapo 02s. He ended up having to get the direct fit ones to remedy the problem.

Also, no reason to have replaced the upper if it was fine.

 

[MS3_KIDD]

a scope? a simple multimeter is all you need for the o2 voltages. ( I suggest a nice scantool though, they pay for themselves quickly)

I second the crap universal 02's, a freind of ine had the same codes with the cheapo 02s. He ended up having to get the direct fit ones to remedy the problem.

Also, no reason to have replaced the upper if it was fine.

ah yes you can use a multimeter too im just so used to hooking up a scantool and grabing the vantage pro or modis and looking at the o2 sensors that way, especially while on the dyno and graphing the reading over time. Its a easy way to find discrepancys between scantool reading and actual sensor outputs

 

[Mike R]

Not many people have scopes

The difference in autozone PN's might be the wire length...

 

[MS3_KIDD]

Not many people have scopes

The difference in autozone PN's might be the wire length...

haha yeah i realize this (silly)

length is a possible reason why PN's are different, arent the connectors different as well? (i believe on my msp they are)

 

[cholland]

Well I looked on the bosch website and they have two different part numbers for the upstream and downstream as well.

The reason i replaced the upstream one is because i was getting close to 100k mi and isnt that about the like or the suggested manufacturer replacement time.

And I know the universal ones are crap, but i financially cant afford to buy the oem ones and they were about a week and a half out to from where I live according to the guys at the front desk at schucks.

 

[slavrenz]

Yes, it is a good idea to replace your front O2 sensor every 100k miles for gas mileage improvement. As for direct fit sensor, go to RockAuto.com and look up your car. I'm willing to bet you can find direct fit sensors for close to the cost of universal ones.

And believe me, I understand the financial issues, but if you have to end up replacing a sensor twice, you're better off getting direct fit and doing it right the first time IMHO.

 

[MS3_KIDD]

I have alldata's. Diagnostic procedure for the PO421 that I will upload when I get out of work 2night