I was checking 02 sensor prices and I noticed some were upstream and some downstream I've only seen the one infront of the firewall(upstream I would assume). Is there a downstream sensor that I haven't seen?


98 SLE

in the cat

After the cat

oops sorry, just after the cat to be more precise IIRC

After the cat and it'* the upstream one that is the problem maker. The down stream O2 checks to see if your cat is working properly

Son of a crap! A buddy of mine scanned the car and said my check engine light was on most likely because of a bad o2 sensor. I thought there was only one.I changed the upstream about four years ago .Do you guys know what code a bad o2 sensor would throw?(I assume both o2 sensors would throw the same code)

There are several codes. No, they are not the same.

0130 HO2S Closed Loop Performance Sensor 1
0131 HO2S low voltage Sensor 1
0132 HO2S high voltage Sensor 1
0133 HO2S slow response Sensor 1
0134 HO2S insufficient activity Sensor 1
0135 HO2S heater performance Sensor 1
0137 HO2S low voltage Sensor 2
0138 HO2S high voltage Sensor 2
0140 HO2S insufficient activity Sensor 2
0141 HO2S heater performance Sensor 2

Thanks Dan I'll ask my buddy for the specific code, thank you sirrrrrr.

Ok it turned out to be the downstream sensor I changed that yesterday,but today the check engine light came back on. So I had it checked at Autozone and the guy said it'* code p403 and p404 and then he said possibly a bad EGR. Is there anyway the EGR code could be related to the o2 sensor I just replaced? And is it normal for both 403 and 404 to pop up at the same time?

98 SLE

It could be a sticking EGR pintel. Can you hear it click when you unplug it?