Any thot on codes the ragtop is throwing

[00 Ragtop Z]

My Z-28 has 114,000 miles on it, and is throwing P00137 and P00157 codes. Thses are O2 sensor codes, specifically they are saying low voltage on both sensors.

Here's the quesion though. My Z is one of teh 2000 models that GM sent out a service notice about extending the warranty on teh cat because of cat failures on the 5.7 l, 2000 models and they'll repalce teh cat free up to 120,000 miles.

Could a cat failure be causing it to throw these codes? In order to have the dealer check it, they want $100 diagnosis fee up front, and I don't want them to just say-it's teh O2 sensors, that'll be $600 when it's actually the cat and they'll get reimbursed for it and never have to tell me.

Oh, and one more thing. I have posted before about having problems with power loss at around 2800 to 3800 RPMS, and that it feels almost like it fuel starvation. Could the O2 sensors (or cat) be causing this, and does that signal at all which one it might be?

Help is greatly appreciated.

[Injuneer]

P0137 = Driver's side after-cat, stationary low voltage
P0157 = Passenger side after-cat, stationary low voltage

The codes set when the voltage remains below 40mV for 380 samples out of a 400 sample lot. Why not just buy 2 new after-cat O2 sensors and replace them yourself. If it doesn't fix it, you are out only a little more than the dealer would have charged you for the diagnostics, and you can be sure he can't say "its the O2 sensors, $600".

Fuel starvation would show up in the pre-cat sensors, not the after-cat sensors.

[00 Ragtop Z]

Fred--as usual, great advice. Anything special I need to think about or consider in replacing the sensors? Haven't done much under the car in a few years but certainly not afraid to get my hands dirty a bit.

[Injuneer]

I don't think there are any issues.... but I don't have after-cat sensors, so I've never changed them.

[00 Ragtop Z]

Couple updates.

Replacement of two O2 sensors after cat, price ranges from $150 (to do it myself), to $270 to $350 at local auto repair shops. Have read that doing it yourself on the ground is a bear to say the least, because they tend to rust in place.

Spoke to a dealer, and asked if it could be related to the catalytic convertor issue on the 2000-2002 5.7l, wherein GM is extending the cat warranty to 120,000 miles or 10 years. Service rep said it is a STRONG possibility that it is actually the cats, so will probably go to the dealer. If they end up saying no, its the sensors, and want to charge an arm or leg, I will go back to one of the repair shops to have it done.

[Injuneer]

You can find out how hard it is by getting an "O2 sensor socket" ($10) and using it on a breaker bar to try to remove one of them. Make sure the exhaust is hot. Since they are after the cats, they should be fairly easy to access. A pair of jackstands should provide you with more than enough clearance. I pulled one out of a 12 year old import with 120K miles on it and it came out with no problems. I've pulled one out of my wife's 9 year old, 88K mile Jeep a couple months ago with no problem.

Do NOT use any sort of rust penetrant on the O2 sensors. The sensors "breath" fresh air through the small passage that the wires run through. They compare the O2 content of the fresh air to the O2 content of the exhaust, to generate the voltage. If you crud the outside of sensor up with rust penetrant, it might destroy it. I changed the one on my wife's car because a drip in the power steering pump had run down onto the outside of the sensor/wires and ruined it.