So I have codes for both rear o2 sensor (PO138 & PO158 Circuit High Voltage).

Since O2 sims completely rule out signals from the rear o2s, I can only assume the o2 sensors aren't the problem. Correct me if I'm wrong, but from the description of the codes and the way the o2 sim is wired in, it sounds like the o2 simulator is failing.

Of course, voltage looks fine when I monitor them with my scanner.

If I do need a new simulator, good luck finding one. Damn!!! I would hate to replace these rusted a$$ cats!!!! Good thing my smog is not due until August!!

Anyway, I need you electrical gurus to verify my initial diagnosis on the cause of the codes.

Thanks

Where are they wired in at? Before or after the harness plug?

well...if you had O2 sims properly wired and got no codes, and you did NOT change the wiring yet you get rear O2 codes now, then yeah either your sims have gone bad or the FRONT O2s are measuring out of tolerance relative to the rears...how are they wired?

Btw, o2simulator.com is in stock last I checked...

Before the ECM harness plug. Per this write-up:

http://forums.maxima.org/5th-generat...tallation.html

I've had this simulator for years. No problems until now...

Good to know. I heard they couldn't sell them anymore.

Tapped the power and ground wires going to ECM connector. Cut the white signal wires.

if you have O2 sims, or one sim with dual output, this code is telling you that they are no good assuming that you had it installed with no codes before. its not a heater circuit code so the O2 sensor is still ok.

High circuit voltage usually means the wire isn't getting as good a signal as it should, have you checked the connections to see if they're loose? What brand SIM are you using?

I know this may not be it, but about a month ago I had all my 02 sensors replaced. Two days later the Check Engine light came on. I took it back to the shop and their basic reader brought up the code for O2 sensors. We checked it again with a more advanced one and got that the gasket is leaking air, which in effect is giving us the O2 sensor code.

Just a thought.

One I bought from O2 simulator.com. I haven't checked the connections. But they were soldered if I remember correctly. Will check them.

A plenum gasket leak huh? Were you getting any lean codes too? What O2 codes were you getting?

BTW, If anyone can build o2 sims. Let me know.

What's weird too is that the little green light on the simulator is blinking like nothing is wrong.

assuming that you cut the signal wire to the O2 like you said, the problem is in either the wiring or the sim. V=IR so if you have high voltage, the problem is that you have too high resistance at some point in the circuit. It could either be a wiring/soldering problem or the sim. Can you remember where you got the sim from and possibly check if they have a resistance reading?

My thoughts precisely.

Unlikely that wiring is the problem. But I will verify. Now, I need to find another o2 simulator. Someone said O2sim.com is back in business. Is that the case?

Every last o2 is Bad on my 00. i plan on replacing one tommorow which one should i replace First? like which one is best to be working so i can slowly replace them.

Fed spec. i think 3 are out maybe 4 codes. 19mpg

Don't thread jack, Travis. You've been around long enough to know how to search. DO IT

i bought my O2 sim dual output from here and it's been on my 02 6spd with obx headers for about 2yrs now without any issues
http://www.3sx.com/store/comersus_vi...?idProduct=769

Great link JonBlz!!! Thanks!!!

^^your welcome bro anytime....i wired up mines just like the write-up on here very easy and taped it all up looks like if it's oem under My hood

When did you get yours? Recently? I take it the company is still selling them?

Ordered and installed simulator from 3SX Performance Automotive. Old simulator looked burnt from being inside engine bay for all those years. Wiring looked OK.

Did drivecycle, reset all monitors. Smogged vehicle. Problem solved.

Thanks to all of you who helped out!!!

good to hear. My dual sim has been going strong since about 2007 but I am not surprised that it might not last forever.

I routed the new one further away from the engine block. Hopefully it will last longer this time around.

i got mines 2yrs ago and it's still working like a charm......i'm glad you got the problem fixed i can imagine the smile it brought to you, just to know the car is 100%