Catalytic converter

My catalytic converter ( one side ) took a crap and I looked them up on line and for my truck they list two sizes ,40.5 in and 46.5 in overall length . My question is how do you measure it ? I want to order the right size the first time . Thanks Jeff

From flange to flange or pipe edge to pipe edge. “Overall length” means the TOTAL length of the unit…

Are you assuming the converter is bad because you got a check engine light and the code read 'Catalyst efficiency below threshold limits", something like that…?? Change the rear oxygen sensor first…That’s that part that generated the code…

Thanks but I’m gettIng a rattle in one of the converters , I wish it was only a sensor . It sounds like a rock bouncing around inside . So I want to buy a direct-fit converter it’s two into one ( right side - left side off the exhaust manifold with a cross over pipe kind of like a lower case h ) my question is from what flange to what flange do I measure from ? Thanks again

Caddyman is still correct. You do NOT know if it’s the converter or the sensor. There are some tests you can perform to determine if it’s the sensor or the converter. But the test is specific to each vehicle and you’ll only find it in a service manual. The cheaper solution is to just replace the sensor. I’d do that first…then if the problem is still there…I’d consider replacing the converter. It really is rare for a converter to fail.

I imagine the two lengths are for std. cab vs extended cab.
I would just get under there, make a few different measurements and see if anything measures 40.5 or 46.5.

Thanks guys I’ll try try the OS first while I’m under the truck take measurements just in case