Is this a Bad Cat or O2 Sensor

647 Views 5 Replies 2 Participants Last post by ndcold, 3 mo ago

ndcold

I have been getting a check engine light recently. P0420 is the error code most of the time as well as a P0101 sometimes. It didn't start happening until I moved to the mountains. Living at 9200' .

I attached some readings while driving. Constant speeds, coasting , accelerating, etc...

Before I go into the shop, I'd like to try and figure this out.

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Downhill Coast

Accelerating

Normal driving

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Lowcountry idn

· #2 · 3 mo ago

Normally I would say P0420 is cats, but your have a MAF sensor error also and your fuel trims are super high.

Clean Your MAF sensor and do the ECU relearn. Also, check the two flex hoses on the air intake - there known to crack which would give you a huge vacuum leak.

If that doesn't correct your fuel trims - replace your MAF sensor

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ndcold

Discussion Starter · #3 · 3 mo ago

Lowcountry idn said:
Normally I would say P0420 is cats, but your have a MAF sensor error also and your fuel trims are super high.

Clean Your MAF sensor and do the ECU relearn. Also, check the two flex hoses on the air intake - there known to crack which would give you a huge vacuum leak.

If that doesn't correct your fuel trims - replace your MAF sensor

I have already tried cleaning and replaced the MAF. I have also checked for leaks doing the spray test. O2 sensors are new as well, but I've heard of them being faulty off the get go. My main concern was the volatility in the B1 O2 downstream. I seems a bit up and down. B2 O2 downstream is gradual like I'd expect. What should I be seeing in the air/fuel ratios?

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Lowcountry idn

· #4 · 3 mo ago

ndcold said:
I have already tried cleaning and replaced the MAF. I have also checked for leaks doing the spray test. O2 sensors are new as well, but I've heard of them being faulty off the get go. My main concern was the volatility in the B1 O2 downstream. I seems a bit up and down. B2 O2 downstream is gradual like I'd expect. What should I be seeing in the air/fuel ratios?

OK, so I see those are actual Air/fuel ratio's - I thought those were your trims as I am used to seeing that as a lambda value where perfect is 1.0. However A/F ratio perfect at 14.7:1 so yours do seem pretty good.

I would double check your long term fuel trims if your reader can - they should be approximately +/- 5%. If they are, then its likely a cat.

But I still don't know why your getting a MAF sensor code? I would figure that out before buying cats. what brand MAF sensor did you use? Was it the same with the old one?

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ndcold

Discussion Starter · #5 · 3 mo ago

Lowcountry idn said:
OK, so I see those are actual Air/fuel ratio's - I thought those were your trims as I am used to seeing that as a lambda value where perfect is 1.0. However A/F ratio perfect at 14.7:1 so yours do seem pretty good.

I would double check your long term fuel trims if your reader can - they should be approximately +/- 5%. If they are, then its likely a cat.

But I still don't know why your getting a MAF sensor code? I would figure that out before buying cats. what brand MAF sensor did you use? Was it the same with the old one?

I went for a drive and tracked the fuel trims. long term does not seem to update. Short term seems to fluctuate with bank 1 a little more volatile than bank 2. Probably related since all the issues seem to be related to bank 1.

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ndcold

Discussion Starter · #6 · 3 mo ago

It was a cat. Had it replaced and all is back to normal. LTFT seems to be working again as well. not sure what that was all about.

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