Postby smj999smj » Tue Nov 27, 2018 1:21 am
Inefficient catalytic converters triggering P0420/P0430 codes are not uncommon on these vehicle, so it could be a bad, upstream converter on the driver's side. However, this code can be caused by other things, as well, such as improper mixture or misfiring. The have been some cracks found at the exhaust flanges near the front air/fuel ratio sensors that have triggered such codes, so it would be best to inspect these areas for an exhaust leak. The rattling could possibly be a loose exhaust shield or broken exhaust shield clamp. Since the vehicle is close to 200,000 miles and almost due for its second set of spark plugs, make sure the plugs are not due for replacement. If the rattling turns out to be broken catalyst substrate, then the converter should be replaced immediately. If it's just inefficient, an O2 sensor spacer can be used on the rear sensor to keep the CEL from triggering, but may or may not pass your state's inspection, depending on how strict they are.
The timing chain issues on the VQ40DE engines don't usually cause a rattling noise, but a "whining" noise that increases/decreases with engine RPM. There are YouTube vids of the noise.
You should also make yourself of the radiator cooler issues that some of these vehicles have that can potentially ruin the automatic transmission, if you aren't aware of it, already.