I have a 2002 Mazda Protege LA with about 240,000 + miles. Been a great car and would like to keep it around 1 more year until my other car is paid off.
For the better part of a year I have had the CEL come on several times and each time it throws the same 2 codes. The first code is the PO421 and the second one is the PO660. Because I know that the second code is often thrown because of the first, I have been focusing on the PO421. Thus far in the last 18-24 months I have replaced:
Spark plugs
Spark plug coils
Radiator
Downstream O2 sensor
Upstream O2 sensor
Starter
The first time these codes where thrown I put some CataClean in the fuel tank to clean out the converter. I followed the directions and it worked. CEL went away on its own. 3 months later, CEL came on...same 2 codes, one more bottle of CataClean. CEL went away on its own. 3 weeks later, CEL cam on,...same two codes, so I go and talk to a guy at Oriellys. He suggested SeaFoam additive. I make the purchase, go out to the car and start the care. I have not yet added the stuff as I needed to wait to fill up, and the CEL goes away by itself. So I wait. A couple weeks later, CEL comes on same two codes... add the Seafoam.. after week, the CEL goes away. Now three weeks ago, the CEL comes on...same two codes. I order the Upstream O2 sensor. The day before I get ready to install it, the CEL goes off by itself. I replace the Upstream sensor anyway. The old one looked real bad when I took it out. Thought for sure that was the problem. Two days later...CEL comes on...same two codes. So now I am at a loss. CEL has been on now since last Monday, so about a week now.
Does anyone have any ideas? Trying not to have to replace the cat converter if I don't have too. I just need it to pass 1 more I section in February as I plan to replace the car some time mid 2018.
Thank you in advance for the help.
For the better part of a year I have had the CEL come on several times and each time it throws the same 2 codes. The first code is the PO421 and the second one is the PO660. Because I know that the second code is often thrown because of the first, I have been focusing on the PO421. Thus far in the last 18-24 months I have replaced:
Spark plugs
Spark plug coils
Radiator
Downstream O2 sensor
Upstream O2 sensor
Starter
The first time these codes where thrown I put some CataClean in the fuel tank to clean out the converter. I followed the directions and it worked. CEL went away on its own. 3 months later, CEL came on...same 2 codes, one more bottle of CataClean. CEL went away on its own. 3 weeks later, CEL cam on,...same two codes, so I go and talk to a guy at Oriellys. He suggested SeaFoam additive. I make the purchase, go out to the car and start the care. I have not yet added the stuff as I needed to wait to fill up, and the CEL goes away by itself. So I wait. A couple weeks later, CEL comes on same two codes... add the Seafoam.. after week, the CEL goes away. Now three weeks ago, the CEL comes on...same two codes. I order the Upstream O2 sensor. The day before I get ready to install it, the CEL goes off by itself. I replace the Upstream sensor anyway. The old one looked real bad when I took it out. Thought for sure that was the problem. Two days later...CEL comes on...same two codes. So now I am at a loss. CEL has been on now since last Monday, so about a week now.
Does anyone have any ideas? Trying not to have to replace the cat converter if I don't have too. I just need it to pass 1 more I section in February as I plan to replace the car some time mid 2018.
Thank you in advance for the help.
