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Ironmike
Ironmike, ASE Master Tech, L1
Category: Car
Satisfied Customers: 3377
Experience:  30 years GM certified, Ford certified
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I have an 2004 isuzu rodeo 3.5 v6 with 57,000 original miles

Customer Question

I have an 2004 isuzu rodeo 3.5 v6 with 57,000 original miles and while driving on a trip recently I activated the cruise and check engine light came on and set a po420 code, I went to the local parts store and that's when they gave me the code. So I changed the down stream O2 based on there recommendation and drove the vehicle again and set the cruise and with in 10 seconds the light came on and the cruise disengaged had it checked again and the store told me same code po420, please help
Submitted: 7 months ago.
Category: Car
Expert:  Ironmike replied 7 months ago.
greetings, Is that the only code found? did the cruise control work?
Expert:  Ironmike replied 7 months ago.
P0420 is for the bank 1 catalytic converter showing it is below efficiency
Expert:  Ironmike replied 7 months ago.
in every case I have seen P0420 set the catalytic converter was bad.
Customer: replied 7 months ago.
Yes the only code and yes the cruise worked prior to this, BUT I forgot to mention that this happened once before a week ago and the napa store cleared the code for me. I had the cat ckd by my brother who owns a exhaust business and he found nothing wrong. So what you think?
Expert:  Ironmike replied 7 months ago.
how did he check the cat, did he check by temp gun?
Expert:  Ironmike replied 7 months ago.
I have seen clearing a cat code work for a short time before. If it just passes the monitor test this can happen. The PCM(computer) does regular checks and when one test on a monitor fails it set the code.
Expert:  Ironmike replied 7 months ago.
​There are ways to bypass the catalyst monitor. Not legal as far as state inspections.
Expert:  Ironmike replied 7 months ago.
I am sure you brother knows this.
Expert:  Ironmike replied 7 months ago.
I have tested catalytic converters with infra red temp guns, need to have at least 50 degrees difference between front to rear. Scanner watching live data is the best.
Customer: replied 7 months ago.
He performed a vacuum test I am not sure about the other test if he performed it, but have you ever seen one set when the cruise is activated?
Expert:  Ironmike replied 7 months ago.
Not sure if they are related. Back pressure gauge is probably what he used. that will only reveal if the catalytic converter is clogging. They can fail and not clog.
Expert:  Ironmike replied 7 months ago.
The cruise could cut out if any faults are detected
Customer: replied 7 months ago.
Are you there?
Expert:  Ironmike replied 7 months ago.
sorry , missed you
Expert:  Ironmike replied 7 months ago.
PCM watches cruise control , like when you step on the brake.