so recently my engine light came on, i found the code for the rear O2 sensor, when I was planning on getting it fix this weekend the engine light came off... is this normal??? or just a false reading

 

This is the same thing I had last March/April. Beware that it could be a bad O2 sensor, or it could mean that your rear catalytic converter is going bad.

I replaced my O2 sensor since it was cheaper and they said that if the O2 sensor is bad it could throw the cat off, and that fixed the problem. But recently my CEL came on and this time it's the rear cat.

I would bet money that it's going to turn on again pretty soon, at which point you will want to do something about it. Hopefully for you it is solved with the O2 sensor, because if not the cat is way more expensive to replace.

 

what gas are you guys using?- thats often a root cause of many problems
the TL needs 91 minimum and prefers 94 as it was designed for
Also Tier 1 grade gas with its extra cleaners is desired or run quality cleaner a few times a year

these are high compression, high performance engines,,treat them as such and be rewarded

We also have a problem with EGR passages getting clogged thru the intake manifold
and need cleaning every 75kmiles--causes freaky running issues when it happens (based on gen2 problem)

O2 sensors can be tested with electrical multimeter before replacement

Cats have a longer warranty than some other parts of the car--federal law
Muffler shops will ck cat with temperature and flow pressure test,
in the usa they have to document the type of failure/reason for replacement- for the feds on every cat replaced

seafoam- 1 can in just under half tank- do that twice and it cleans all the fuel and combustion internals,, and the cat too!

If you are past warranty or have modded the exhaust, see our vendor Excelerate for several choices in cats from street to sweet,,for a few hundred instead of a thousand dollars!!

 

always remember codes are CLUES not diagnosis in themself
and are often false or leading you somewhere to a solution

ck battery voltage and electrical system at parts stores for free
That a leading cause of probs in winter,,low volts = false codes and poor running

 

Could be a false/spurious event. The ECM/PCM will monitor the event for a period of time. If it doesn't occur again within this time, it will turn off the CEL.

I'd just wait and see if the CEL comes back on. If it doesn't, it was probably just a spurious signal. If it does, then we can troubleshoot the exact code.

In the meantime, do you have any engine/intake/exhaust mods? Have you been doing any work in the engine compartment?

 

That's news to me...

 

It just came on again today... No, mods yet... two different shops ran the same code as the rear O2 sensor..

 

Same story as me basically.

Changed spark plugs myself.

After 5 days, CEL goes on.

I tighten the spark plugs some more, then no more CEL for a bit.

Then CEL goes back on so I'm like wtf so I went to a mechanic and he pulled the code and said I had a bad O2 sensor.

Got a new one put in, and never got the CEL again.

 

OK, then it's likely you have an issue. What was the code#?