i have a 2001 gs300 with 70,000 miles on it and i failed my smog check. the smog guy said my emissions are high and my car is now a gross polluter. the check engine light is on and the code tells me the the oxygen sensors are bad, bank 1 sensor 1 and bank 2 sensor 1 i replace both sensors with denso sensors from rock auto. after i replace the sensor i drove my car for 100 miles to make sure the check engine didn't come back on and it didn't. then yesterday i took it to get smog, and it fail. when driving back from the smog place the check engine light came on again. can some please help me out why my car's check engine keep saying the oxygen sensors are bad when i replace them. i also had a srt intake with ecu on my car when the check engine light first came on, i now have the stock intake back on. please help.

There are several different codes for the O2 sensors, you need to find out what specific code you have because the procedure for troubleshooting is dependant on the specific code.

hey george this is what the smog mechanic sayed. pulled codes and found codes p0130 o2 sensor circuit fault bank 1 sensor 1, p0133 02 sensor circuit slow response bank 1 sensor 1, p0153 02 sensor circuit slow response bank 2 sensor 1, and p0150 02 sensor circuit fault bank 2 sensor 1.

I do not have access to my manuals (I'm at work now), but at this time I would suggest checking the fuse for the O2 heaters. Most cars use 1 fuse for the O2 sensors, if that fuse is blown, you would get a circuit failure and slow response. I will look up the codes later and give you some more details then.

Ok I have had a chance to check my manuals, those codes are not for the heater circuit. Start by looking for leaks in the air intake. Look for split hoses (especially to the pvc). Then check fuel pressure. If you do not have a gauge to check fuel pressure, I would suggest changing the fuel filter. In case you are not aware of this, you car has the fuel filter located inside the fuel tank. If you remove the rear seat, you will see a acess cover that allows you to pull out the entire pump, fuel level sender, and filter assembly.

the fuel filters on our car are a lifetime part and almost NEVER require replacing unless your doing major mods

Yes, but that does not preclude the possibility of a bad tank of gas. This car has relitively low mileage, I would not expect to see these type of error codes at this mileage.

thanks for the information im going to check the air box and hoses today.

I just wanted to let everybody know what had happened to my car, and what the problem was. I decide to take my car to a local mechanic to find out why the check engine kept telling me my oxygen sensors where bad when i replace them with new ones. It turns out there was nothing wrong with oxygen sensors, some how a rodent, mice or rat had chew and damage the wires at the e.c.m the mechanic replace the damage wires and now my car has passed its smog check. So if anybody gets the codes po130,133 po150,153 and cant pass there smog test check the wires at the e.c.m

thanks for letting us know!

How much did he charge you to replace the wire in the ECM and what color was it?

"WIRES" Every wire to the ECU is a different coded color, I am suspect to the mechanics diagnosis, I know the amount of protection that is on the harness that leads to and from the ECU, Either it was the biggest rat on the planet or there is a faulty connector. Really, The main harness needs to be cut with paul bunyons axe............And Blue has to chew on it for a week

Check the oxygen sensor wire, i replace the o2 sensor and it came on still, it turn on to be one of the o2 sensor wire was loose, ever since then light never came on again.

there were a few wires he had to replace, i dont know what color they were. he charge me $320 and that was all labor. $15 for parts.