I have an '06 SuperCrew 4wd Lariat, 125k miles and I'm wondering if I have the beginnings of a cat issue. I started it the other day in a garage and accidentally leaned on the gas too much and heard a lot of banging around underneath the truck. I duplicated the scenario a couple of times. I have also noticed a noise that sounds like a pulley starting to go when I have the back slider open. The noise only occurs when I'm on the gas, but, when I open the hood I don't hear anything coming from the engine compartment. So, I'm wondering if it's coming from the exhaust pipe. I got under the truck and tapped the pipes and cats with a rubber mallet and it seems that the only place I hear rattling is in the cross pipe that connects the driver side exhaust to the pipe leading to the muffler. This truck has one cat per side. The heat shields are firmly in place. I am not experiencing issues with the truck hesitating or stalling.

Any ideas on how to diagnose this more accurately?

 

the CEL light will come on well before you have an excessive CAT problem. I would not worry about it right now. Without the CEL, your working blind.

 

The MIL will come on (with converter-related DTCs) ONLY if the self-tests that monitor catalytic converter performance fails. The converter can still fail mechanically without failing the performance self-tests.

IOW, the presence or absence of the MIL is not a definitive indicator (or lack thereof).

 

project....... I don't understand how the converter could fail mechanically and not set off a code... do you have an example of what could happen ?

 

A symptom that I think I'm having is it sounds to me like there are some broken pieces of the cat medium in the cross pipe. Not enough to choke the system now, but, if it breaks up any more it could possibly leave me stranded.

 

It will set of a code ONLY if it isn't working CHEMICALLY, that is, the catalytic action is no longer performing its job of oxygen storage.

It is still possible that portions of the "brick" physically break off and rattle around but the remaining catalyst structure still performs.