Help with OBDII codes

[will4384]

yesterday I noticed the check engine soon light came on in my car. I rented a scan tool from NAPA, and I got two codes. P0133 (O2 sensor CKT slow response), and P0404 (EGR flow CKT range/perf). What do I need to do with the O2 sensor. Should I just replace it? How much do they cost? I'm planning on cleaning the EGR and seeing if that takes care of the P0404 code.

Thanks

[will4384]

hey, I just found this on another post.

Conditions for Setting the DTC
DTC P0133
This DTC is set if the average response time of the switches from the sensor is too slow after the 100 second test is performed. If the lean to rich time is greater than 125 ms or the rich to lean time is greater than 156 ms, this code will set.

DTC P1133
If less than 10 switches take place during the test, this code will set.

DTC P1134
If the transition ratio of the sensor is greater than 2.8 or less than 0.6, this DTC will set.

Diagnostic Aids
Repair Procedure
The oxygen sensor wiring and connections should be checked if any of these DTCs are set because corrosion or loose connections could cause these DTCs to set.
The most likely cause of setting any of these DTCs is contamination. This contamination could be caused by fuel, improper use of RTV sealant, engine oil, or coolant contamination.
The source of contamination should be identified and corrected before replacing the sensor.

So I should be looking for contaminates? I did notice that the coolant level was alittle lower than I remember it being about 2 weeks ago.

Thanks

[Gerry Proctor]

An O2 sensor switches about six times per second. Yours is slow, which is usually a sign that it has seen better days. This is about the only indicator of a sensor that needs replacing. If your engine is putting coolant into the combustion chamber, then you're looking at a head gasket or a breach of the cooling system (like cracked head) into the combustion chamber. Coolant into the combustion chamber is usually associated with other issues, and you don't mention those so it's not likely you have that as an issue.