I have an 02 Montero Sport XLS. My service engine soon light recently came on. I tested and found the following OBD II codes:

P0158 - O2 Sensor Circuit High Volts
P0161 - O2 Sensor Heater Circuit
*Both Bank 2 Sensor 2

I have since found out what Bank 2 Sensor 2 is. The engine has also developed a louder than normal exhaust, coming from the lower engine area, near the passenger side firewall of the engine compartment. I did a visual inspection of the exhaust leaving the engine back to the catalytic converter. I found no obvious leaks in the exhaust. The catalytic converter looks all but miserable, but the noise isn't coming from there. I haven't done any diagnostics on the sensors themselves. Based on the louder than normal exhaust, I was thinking the problem may be a leak.

Questions:
- Is it possible that the O2 sensor failure could be causing the louder exhaust tone near the engine?
- More generally, does this sound like a problem of O2 Sensor failure or exhaust leak?

I'm not sure where to go from here. I'd hate to buy and replace an O2 sensor if it's just an exhaust leak. Neither will be cheap, but for me, mechanical is easier than electrical. And if new sensors come with certain pipes then it'd suck to buy sensors then pipes because new sensors weren't the problem.

My Monty has 147300 miles. It had an oil leak (valve cover gaskets) that I recently repaired. I replaced the valve cover and plug gaskets, plugs and changed the oil and filter while I had it apart. While I had it open, I found oil on the inside top of the plug connectors and a residue inside the plenum tubes that looked like the result of the engine burning rich. The old plugs also looked like the engine has been running rich. The valve cover screws were extremely loose and the old plug gaskets were bent up. It looked like someone had the covers off before and tried to stuff the old plug gaskets through the holes in the top of the valve cover rather then allow the valve cover to rest against the plug gasket and create a pressure seal against the metal.

Any advice available is greatly appreciated.

Chris

 

Have you removed the heat shield and checked to see if the exhaust manifold is cracked? I had this happen three times on my 1999 Sport Limited (3.5L) and when the crack got big enough (to where the exhaust noise was audible from the crack) it always threw O2 sensor related codes (can't remember exactly which ones). I haven't had a manifold crack on my 2003 yet but what you are describing sounds awfully familiar.

 

No I haven't. I will take a look. If it's located where I think it is, that could be precisely where the louder tone is coming from. Thanks for the info.

 

BTW, is there any exhaust-like smells under the hood or inside the cabin?