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

From my previous thread I was told that one 02 sensor provides driveability settings, fuel, timing, etc. and the post cat gives me that CEL. I was told that if I switch the sensors and I get the same code, it means I have a bad CAT, if the code changes to indicate the other side, then it's a bad sensors.

Well I switched the sensors and I have the same CEL. HOWEVER, just reading back, I didn't "reset the codes", which I don't know how to do that. Shouldn't the truck automatically update when I turn it on? The CEL turned on right away like before, like if there was no change.

If i do have a bad cat, I have a small bag of tools, how hard is it to fix, and if I take it to the shop, how much am I expected to pay?

To reset the ECU remove the fuse for it (located in the fuse box in the engine compartment) for 20 minutes or so. Doesnt always work but usually does. CEL codes will only go away after a certain number of cycles while driving. Sometimes its a few minutes, sometimes it can take weeks.

For cat converter replacement you are probably better off taking it somewhere and having an aftermarket one welded in. OEM ones can usually be changed fairly easy with basic hand tools since the pipe and flanges are already attached. But, OEM ones cost around $650-750 each (depending on vehicle and transmission). Having aftermarket ones welded in should be much much cheaper.

But, OEM ones cost around $650-750 each (depending on vehicle and transmission). Having aftermarket ones welded in should be much much cheaper.

some of the ones from toyota are as much as 1700$ (V-6, V-8) if you go aftermarket just make sure the cat is certified! mike

Ok, I didn't exactly see a fuse for CEL, but I didn't see one for ECM. not know what that meant, i left it alone. But I think I confused myself, there was a fuse for 02 sensor and I took that one off. I'm going to leave it off until I leave work and see what I get.

Ok, I didn't exactly see a fuse for CEL, but I didn't see one for ECM. not know what that meant, i left it alone. But I think I confused myself, there was a fuse for 02 sensor and I took that one off. I'm going to leave it off until I leave work and see what I get.the fuse to remove *is* the ECM (which is what sets the CEL). just remove it for 30 seconds.

or if you prefer unhook the battery which will do the same thing except you will have to reset your radio presets.

//bc

From my previous thread I was told that one 02 sensor provides driveability settings, fuel, timing, etc. and the post cat gives me that CEL. I was told that if I switch the sensors and I get the same code, it means I have a bad CAT, if the code changes to indicate the other side, then it's a bad sensors.

Well I switched the sensors and I have the same CEL. HOWEVER, just reading back, I didn't "reset the codes", which I don't know how to do that. Shouldn't the truck automatically update when I turn it on? The CEL turned on right away like before, like if there was no change.

If i do have a bad cat, I have a small bag of tools, how hard is it to fix, and if I take it to the shop, how much am I expected to pay?


Not sure you understood my advice so I will clarify: You want to switch the post cat sensors with each other. There are two cats and two sets of o2 sensors. One before and after each cat. Don't switch them front to back and back to front. Switch the post cat sensors with each other.

You should be able to have your codes erased anywhere that will read them. Usually you can find an auto parts store that has a scanner capable of clearing codes.

Not sure you understood my advice so I will clarify: You want to switch the post cat sensors with each other. There are two cats and two sets of o2 sensors. One before and after each cat. Don't switch them front to back and back to front. Switch the post cat sensors with each other.

You should be able to have your codes erased anywhere that will read them. Usually you can find an auto parts store that has a scanner capable of clearing codes.


Oh, I didn't know there were two cats. So exchange the two Post cat sensors. I think the side i switched was the first that I saw and that's why I only focused there. i'll keep looking and see if I can switch those back. I did unhook my battery, the CEL is off for now, but I'm sure i'll come up again.

But I need to make sure I switch those.

Oh, I didn't know there were two cats

Depends on the vehicle. On some years automatics had 2 cats but 5 speeds only had one. On 2nd gens autos and manuals both have 2 cats.

Depends on the vehicle. On some years automatics had 2 cats but 5 speeds only had one. On 2nd gens autos and manuals both have 2 cats.


Ok, I didn't know this so you could only have one cat. You'll just have the check it out or if it won't break your budget, just replace the post cat sensor with a new one. If the code returns, replace the cat.