Folks:
2008 Denali XL. At about mile 81,000 I get the lovely and famous P0420 (Catalyst System Efficiency Below Threshold (Bank 1)) code with check engine light on dash.
- I cleared it hoping there was just some anomaly in the system. 2 days later, it comes on again.
- I replaced the downstream 02 sensor about a week later and reset the code then.
- Few days later (100 miles or so) it shows up again.
- I get desperate and try the Cataclean. Expensive stuff, for sure. I follow instructions exactly. I did NOT get a chance to reset the code.
- About 50 miles later check engine light is off (meaning the light on the dash is gone but I didn't reset any code). I figured the cataclean worked and I'm shocked, since I've long felt that kind of stuff is more snake oil than science (sorry to offend some of you). But I'm left wondering if codes can just go away. I thought you had to reset them.
- About a two weeks later and maybe 4 to 500 miles more, light and same error code comes on again.
- We drive it with the light on for at least 3 weeks (1000 miles due to road trip). Got in Yukon just last night and the light IS off. not pulled code or memory from system, light is no longer on.
I thought such codes had to be cleared for the light to come off? I don't understand.
So my questions are:
1) Do the codes sometimes reset? Meaning does the computer run tests on failed areas to see if they are cleared?
2) Could bad or ethanol gas be causing such an error code? I've tapped the Cat and I don't hear any rattle; replaced downstream O2.
3) Would any of you replace the Cat at this point? That's a lot of cash to throw at something that comes and goes like this.
Troubling
2008 Denali XL. At about mile 81,000 I get the lovely and famous P0420 (Catalyst System Efficiency Below Threshold (Bank 1)) code with check engine light on dash.
- I cleared it hoping there was just some anomaly in the system. 2 days later, it comes on again.
- I replaced the downstream 02 sensor about a week later and reset the code then.
- Few days later (100 miles or so) it shows up again.
- I get desperate and try the Cataclean. Expensive stuff, for sure. I follow instructions exactly. I did NOT get a chance to reset the code.
- About 50 miles later check engine light is off (meaning the light on the dash is gone but I didn't reset any code). I figured the cataclean worked and I'm shocked, since I've long felt that kind of stuff is more snake oil than science (sorry to offend some of you). But I'm left wondering if codes can just go away. I thought you had to reset them.
- About a two weeks later and maybe 4 to 500 miles more, light and same error code comes on again.
- We drive it with the light on for at least 3 weeks (1000 miles due to road trip). Got in Yukon just last night and the light IS off. not pulled code or memory from system, light is no longer on.
I thought such codes had to be cleared for the light to come off? I don't understand.
So my questions are:
1) Do the codes sometimes reset? Meaning does the computer run tests on failed areas to see if they are cleared?
2) Could bad or ethanol gas be causing such an error code? I've tapped the Cat and I don't hear any rattle; replaced downstream O2.
3) Would any of you replace the Cat at this point? That's a lot of cash to throw at something that comes and goes like this.
Troubling
