2000 Solara P0125 Question

[SmitsYoda]

Ok so my mom has a 2000 solara since the day we got the car her check engine light has been on. We took it to autozone and they check it out as a faulty o2 sensor *manifold*. I changed it out for her reset the car and the check engine light stayed off for a few days and came back on. I reset it again and it stayed off for another 2 weeks then it came back on. What else could be the cause from this? Does her cat need replaced? I'm trying to save her money also she said her gas mileage isn't that good.


NOTE I Meant P0420!

[hill8570]

Is this a 4-banger or 6-banger?

What's the code(s) at the current time? Still P0125, or have you not re-read the code(s) since the O2 sensor swap?

This code means that the upstream O2 sensor(s) aren't ever seeing a RICH condition at operational speeds.

Generally, I'd expect the problem to be a fuel system (injectors, etc.), ignition (plugs, wires), or hole in exhaust problem unless there were other codes beside the P0125. A lot of possibilities, unfortunately. Do you know a decent independent mechanic? This is one of those nasty codes where there are a lot of possibilities, and the easiest way to narrow things down is to have a good test tool that will give you the output of the various sensors in the car while it's operating (freeze frame). You could spend a lot of time and labor just shotgunning the problem.

[SmitsYoda]

Sorry i meant PO420

[hill8570]

P0420 (Catalyst efficiency below threshold) often means a dodgy cat, especially if the mileage is >150K miles. It can be other things, 'tho -- an exhaust system leak upstream of the cat (letting in too much oxygen), or a badly tuned engine. "Gas mileage isn't that good" isn't real precise, but if mileage has dropped significantly from new it would be worth tracking down what's up with that -- if she's running rich due to poor plugs, wires, etc. then that poor cat is having to clean up a lot of crap it shouldn't have to, which could lead to a P0420. A bad cat by itself won't cause bad mileage unless it's actually clogged and restricting the exhaust flow...that's usually pretty easy to tell, since performance really starts to suck.

[SmitsYoda]

So where should i start? Should i tell her to replace the cat or should i try the plugs and wires? I changed the front 02 and it did not help. She wants the check engine light to go off.

[SmitsYoda]

So guys the car has had the check engine light one since we had it. I'm trying to solve my mom money but she wants the CEL to go away she said her gas mileage isn't good either. if i changed the plugs and wires do you think that would fix it? I'm trying to help her out as much as possible.

[fenixus]

Originally Posted by SmitsYoda

So guys the car has had the check engine light one since we had it. I'm trying to solve my mom money but she wants the CEL to go away she said her gas mileage isn't good either. if i changed the plugs and wires do you think that would fix it? I'm trying to help her out as much as possible.

no, it won't fix P0420. it may help healing some of MPG issues you having.

to get rid off P0420 code, you would need to track it down and there are several things that need to be checked (including upstream exhaust leak). most likely car has a shot upstream catalytic converter though, since it was driven with bad upstream o2 sensor since you bought it. this may have plugged the cat with all the crap resulting from untuned engine operation (false o2 readings received by ECU).

however if you replace plugs & wires and all filters (fuel & air) and then you still have MPG issues, then there will be only 2 more things responsible for it: bad catalytic converter (likely in your case) or clogged fuel injectors (unlikely).

of course you can go ahead and replace the front cat, but this is a shot in the dark, there is no guarantee this is the root cause. for some people issue was coming back even after replacing it.

more here:
http://www.camrystuff.com/manuals/Gen4/Diagnostics.pdf
for 5s-fe engine (4 cylinder):
page DI-116 for Federal emissions type (regular upstream o2 sensor)
page DI-119 for California emissions type (wideband A/F upstream sensor)

[SmitsYoda]

So if i change the cat will that take away the CEL?

I'm putting no plugs and wires in for her here soon. If i do change the cat what brand should i go with? The 2.2 has only one cat right? Sometimes if i drive her car for a while i can feel heat inside the car i dunno if that's from where the cat could be clogged or what.