i hate engine codes can u help

I took the 99 xj for emissions today with no worries. Boy was I wrong 2 blocks for the building the light comes on so I stop at the closes lot unhook the vattery for 10 mins and put it togethr for the test. The lights wasn't on but I didn't clear the computer so I Failed. My codes were P0138- the 02 sensor and P1492-ambient battery sensor. My ?s are how do I tell what 02 sensor and then what the hell is an ambient battery sensor, where do I find it , and any idea how to fix it ? I need these done asap bc my sticker was up in Jan and thy won't renew it till I pass thanks

ambient battery sensor is that little round black plastic cap looking thing in the battery tray, right under the battery. Not sure what's wrong with it, though.

O2 sensor (O the letter, not 0 the number - it's the chemical formula for atmospheric oxygen, I see this a lot and it confounds the search so I figured I'd mention it) should be giving further info about which one it is from my understanding, what did you use to read the codes?

im going from the codes they gave me at the test facility. i looked up the codes on the crackberry and i no the O not 0 it was easier to do wht i did while driving. thanks though.

i read the battery can be bypassed but it doesnt explain how. can anyone here

Check the battery sensor wiring for bare, broken, shorted, might be simple,fast repair with luck.

That code is for the downstream O2 sensor (bank 1, sensor 2 short to voltage). It's pretty common, and I've found that mine (the light, at least) comes and goes, in part, it seems, depending on the gas. Every once in a while it comes on after a hot start if I'm driving in traffic, stays on for a while, then goes off. That means if you have access to a code reader, you could probably clear the code and have it stay off for quite a while, at least for long enough to pass emissions.

That's the thing with emissions tests. You can't have a P1000 in memory- which is the code generated when others are erased. The P1000 goes away when the computer has completed and passed all emissions monitors. It can take a couple days to go away, which is why you should never plan on erasing a code right before going to the smog shop.

Here is a link that explains your P0138 oxygen sensor code. The most likely cause is the sensor itself. Unless you find something amiss within that circuit, replacing that sensor would be the next step. As long as you're at it and if you intend to keep the vehicle, consider replacing BOTH the upstream and the downstream sensors.

http://www.obd-codes.com/p0138

For the P1492 code, Pull out the battery and tray to look at the connector/wires. Sometimes there is damage due to battery acid and you might be able to repair. If not, you'll need to replace that sensor. About $30 give or take if memory serves me.