P0240: Catalyst System Efficiency Below Threshold (Bank 1) with pictures!

spider1 · 10-30-2007, 11:48 AM

I drive a 3.2L 1996 Isuzu Rodeo LS. My check engine light came on and I took it to autozone. They said that I had an error P0240 Catalyst System Efficiency Below Threshold (bank 1). The guy told me that if it was the catalytic converter that the car wouldn't be running, so he said that it probably has to do with the sensors. Although someone at work told me that it doesn't necessarily stop working, just the performance my be slow. So i have to keep on eye on that.

For now I want to replace the sensors to see if they are the problem. Either one or both are gone bad. So i wanted to see if anyone has changed these out and had an difficulty. I took pictures of what I figured looked like the sensors and I want to see if these are it. Let me know what yal think.

First Sensor:

http://s42.photobucket.com/albums/e3...t=IMG_4292.jpg

Second Sensor From Far:
http://s42.photobucket.com/albums/e3...t=IMG_4293.jpg

Second Sensor from close:
http://s42.photobucket.com/albums/e3...t=IMG_4295.jpg

pharm_rodeo · 10-30-2007, 04:31 PM

Just O2 sensors. Warm up the truck for a few minutes before you try and remove them.

trooperbc · 10-30-2007, 08:06 PM

the O2 sensor before the catalytic converter is the one that provides info to the computer for changing the driveability settings, fuel, timing, etc.

the O2 sensor after the catalytic converter provides the info to set the CEL code that you got.

so if it is the O2 sensor that is the problem, just change the first one; your post-cat is probably working, although it could be defectively setting the code.

the vehicle will run just fine without a cat converter, it's an after-the-fact component that doesn't affect the engine in any way. if it were to get plugged up which some have, then that would be an exhaust restriction which would slog you down.

FL 3.2L · 10-30-2007, 08:57 PM

Since you're heading back under there....

Would you tell me what the bracket that holds the O2 sensor connector is bolted to? The last time the truck was in the shop, the mechanic didn't feel it was necessary to bolt it back up. I can't seem to find a place to bolt the bracket. The connector is still attached to the bracket which hangs freely just above the exhaust.

I'd appreciate greatly!!

spider1 · 10-30-2007, 10:56 PM

I'm assuming you mean that the post-cat sensor is the second picture I have up there? The one that is further up in the truck. Towards the front end of the truck? Sure thing,I'll let you know.

spider1 · 10-30-2007, 10:57 PM

is the second picture the post sensor?

trooperbc · 10-31-2007, 12:21 AM

Quote:

Originally Posted by spider1

is the second picture the post sensor?

"post cat" means *after* the cat, which means towards the exhaust.
"pre-cat" would be *before* the cat, meaning towards the engine.
here's an illustration from the isuzu online parts site www.myisuzuparts.com

mmm later, it's not working now. give it a try, it's a very valuable resource for those without the factory manuals from www.helminc.com

//bc

Cat Fuzz · 10-31-2007, 12:30 AM

One way to check if it's the o2 sensor or if the cat is bad is to switch the two after cat o2 sensors. Clear the codes and drive until a code resets. If its the same code, bad cat, if the code changes to indicate the other side, bad o2 sensor.

FL 3.2L · 10-31-2007, 08:42 PM

The bracket is actually bolted somewhere on the passenger side of the tranny. It's for the sensor on the passenger side. There is wiring which travels over the top of the transmission from the driver's side to this bracket, too. I found it on myisuzuparts.com, but it is a little vague about where it bolts up.

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