Installed Exhaust/cleaned K&N - now CEL!

[Bilulan]

A couple weeks back, I installed an exhaust, used liq. wrench pretty liberally on the bolts, then fired it up for a few mile test drive. All was well. When I parked in the garage, I had a steamy burning smell from the lower rear engine area. I considered it to be any excess liq wrench burn off of the exhaust and no biggy. I restarted approx 2 more times that day w/ no CEL's.

The next day I cleaned & reoiled my K&N air filter. (I have cleaned it two previous times w/ no prob.) After starting the car up, I immediately got a CEL and TCS permanently on. I reset the code a few times that day thinking it was from the air filter cleaning. All was well for 7 to 10 days. The past 4 days I have not been able to keep the CEL/TCS from coming on. Immediately after it is reset, it comes on at start up. If I drive a few minutes, turn the car off, then restart, the TCS stops coming on, however, the Check engine light is still there.

I jumped the Service Connector and got the CEL flashing 4x's slowly and then 2x's quick. This may seem obvious, but is that code 42 - bad Rear O2 sensor?

Any thoughts?

 

[bjmills]

I'm pretty sure that code is one of the O2 sensors, yup. Is it possible you knocked a connection loose installing the exhaust? I'd pull the connector, look at it closely, and put it back in...

 

[Bilulan]

Craziest thing again happening. I went through the service manual and measured the voltage of the rear o2 primary sensor (as Larry B pointed me to that one.) When I unplugged the connector from the ECM to insert the test probe, I plugged it back in and started the car up. The check engine light went away. The wire measured .9 volts as it should. The CEL actually didn't come back on tonight after letting the car sit since noon today. Not sure what to think.

When o2 sensors go bad, are they fluky? Streaks where they will trigger a CEL and then other times they don't?