I recently purchased a used 2004 Toyota Highlander v6 4wd from a dealership with 120k miles. The check engine light came on with P0420 as the only trouble code. I took it into a shop for further diagnosis - this was also my first attempt at a “general inspection” of the vehicle, but im not sure what all was examined. I decided not to replace the catalytic converters (they recommended that I replace both) as they are very expensive. Recently, the vehicle has been hesitating to accelerate mostly with heavy acceleration. I have read some info online suggesting this can be related to misfires with various causes. P0420 is still the only code I’m getting, but I’m not sure if they checked out everything that could possibly cause a misfire. At first I thought that any other issue should trigger a code as well if it were the case, but i don’t know what all sensors this vehicle specifically has, and wonder if there could be something the computer doesn’t see. The vehicle still gets up to 65mph and above with no abnormalities, apart from the slight delay before it downshifts to accelerate. I don’t want to replace catalytic converters if I don’t absolutely have to since I can’t really afford it, especially if there could be something else causing both cat failure and the acceleration issue. What should I do to diagnose? Or is it likely the converters causing all of this?
I recently purchased a used 2004 Toyota Highlander v6 4wd from a dealership with 120k miles.
What kind of dealer is selling 20-year-old cars? Is anything known about its service history?
The check engine light came on with P0420 as the only trouble code.
Wasn't this problem discovered during the pre-purchase inspection? Is there anything suspicious in live data?
What should I do to diagnose? Or is it likely the converters causing all of this?
Although P0420 frequently is caused by bad catalytic converters there are other issues that can trigger it. See the following for possible causes and diagnostic procedures:
https://www.walkerexhaust.com/support/tech-tips/diagnosing-catalytic-converter-p0420-code.html
https://www.way.com/blog/p0420-code-what-it-is-and-how-to-fix-it/
https://www.carparts.com/blog/p0420-code-catalyst-system-efficiency-below-threshold-bank-1-2-2/
P0420 can be caused by a number of things. The catalytic converter is designed for the lifetime of the vehicle (it never "runs out", unless there are issues with the engine). More often than not, the catalytic converter is welded to the exhaust, so a mechanic will also need to weld. My Ford Ranger has 292k miles on it, and it's still on the original cats. Vacuum leaks are highly suspect for a 19-year-old car. All of the rubber hoses should be replaced, first. That's the lowest hanging fruit. Get a scan tool, if you don't have one already, and do some analysis.
Just do a tune up first and see if that'll help. Check spark plugs (replace if old), clean throttle body and MAF sensor, add 505CRF to fuel, check for vacuum leaks, etc., etc.
