# P0422 pending b1s2 o2 99.2% and bad mpg



## peepsRawsome (Jan 13, 2009)

I have a 99.5 golf 2.0 automatic
It currently has 120,xxx miles and I really want to figure out what i need to do to restore the performance/ efficiency of my Vw. 

Problems:
P0422 code pending 
Bank 1 sensor 2 reading 99.2% and not fluctuating 
Really bad mpg around 15 hwy
Loss of power
When driving if I give it some gas it no change in acceleration and If I floor it it just down shifts and goes a tad bit faster
I can barely keep up with traffic without having to punch it

The car has ran good since I bought it
It's just getting slower recently 

Btw it's completely stock other than the cat,

I have replaced the following:
Aftermarket cat 1 year ago 
Coil, plugs and wires 1 year ago
Timing service 6 months ago
Transmission service 6 months ago
Plugs and fuel filter 6 months ago
Air filter and oil change 2 months ago
Purge valve 1 month ago


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## peepsRawsome (Jan 13, 2009)

Since the code is bank 1 efficiency below threshold then maybe a o2 cheater will fix it.
I've heard that aftermarket catalytic converters are not as dense so there's more emissions at the downstream o2 sensor which is causing the fault.


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## peepsRawsome (Jan 13, 2009)

Can anyone help


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## Anony00GT (Mar 6, 2002)

Do you have VCDS or just generic OBDII?

If VCDS, post up a full scan, at least of the engine portion. Also values in measuring block 032.

I'm thinking bad MAF, along with possibly a clogged CAT.


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## peepsRawsome (Jan 13, 2009)

I do not have vag com but my scanner has live data if that helps, could be maf it's the original


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## peepsRawsome (Jan 13, 2009)

What's in 032? Is that the maf?


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## Anony00GT (Mar 6, 2002)

032 is Lambda adaptations, idle and load.

What are your fuel trim numbers?


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## peepsRawsome (Jan 13, 2009)

Ok at idle cold start was 
short 0.0
long 0.8 
and after normal temp 
Short: bouncing from -3.1 all the way to 3.1 sometimes as low as -11.0
Long: stuck at 1.6
Rpm 780- 815
Spark advance 6.0
IAT 35°C
MaF g/s 2.90 - 3.12
Tps 2.0 - 2.7
Load 2.7 %
ECT 100°C
O2s b1s1 Volt 0.090 - 0.750
O2s b1s2 Volt 0.140 - 0.750
Stft b1s1% -3.1 - 3.1 
Stft b1s2% 99.2


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## Anony00GT (Mar 6, 2002)

CAT is toast.

Replace it and test MAF.


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## peepsRawsome (Jan 13, 2009)

Darn.. It's only a year old???


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## peepsRawsome (Jan 13, 2009)

Is it clogged or too much flow?
I forgot to add that at night it has much more power and shifts smoother


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## Anony00GT (Mar 6, 2002)

Based on O2 sensor values it's not doing anything (hollow/too much flow). But your power description seems to indicate it's clogged. Either way, you get what you pay for with cheap aftermarket cat.

That being said, if the MAF isn't operating properly, that can cause power loss, MPG issues, and easily kill a cat in under a year as well.

Disconnect the cat and drive down the road open header for diagnostic purposes, see if the power comes back. If it does, record the highest achieved MAF reading (g/s) during a WOT blast to the redline. Wear earplugs, it'll be loud


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## peepsRawsome (Jan 13, 2009)

Ok wow


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## peepsRawsome (Jan 13, 2009)

I jus got another code for a random misfire fuel level too low...??? That's what the code said and I never go below 1/4 tank

Edit: this was before anything you said to do


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## peepsRawsome (Jan 13, 2009)

I really appreciate the help


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## Anony00GT (Mar 6, 2002)

Need to definitively make sure the cat isn't clogged, then commence MAF testing.


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## peepsRawsome (Jan 13, 2009)

Ok removed cat and it runs the same I guess it's hard to think about it with it being so loud, highest maf reading was 85.0 give or take


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## Anony00GT (Mar 6, 2002)

That MAF reading is a little low, replace it with a quality or known good unit of the exact same part number.

Replace the CAT. You should be under warranty from the manufacturer still.


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## peepsRawsome (Jan 13, 2009)

Ok I have one ordered, no warranty with the cat, I bought it from Craigslist but it was new in the box. So since the after cat o2 sensor is telling me "bad or faulty cat" it's dumping fuel ?? Or is the maf the one doing that? Also is the rich mixture causing power loss?


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## Anony00GT (Mar 6, 2002)

I'm basing this on generic OBDII readings, which aren't as good as VCDS blocks. But that's all we have to work with.

A downstream O2 sensor that fluctuates between 0.140-0.750 (roughly matching the upstream sensor) indicates the catalytic converter is either hollow, not present, or not working.

The fuel trim issue can cause power loss, and that is caused by the MAF. Catalyst breakdown is also caused by the fuel imbalance, and/or just a cheap Chinese cat.


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## peepsRawsome (Jan 13, 2009)

We'll I replaced the maf with a factory new and replaced cat with o2's all factory new 
And I feel like I should have called it quits and sold the thing but.... I love my Vw 

The power is back for the most part and mpg is way better, but for some reason today I drove it to work and it ran beautiful and now leaving work it's lost power and feels like something is pulling the timing


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## Anony00GT (Mar 6, 2002)

Start over, pull codes.

Did you get the OE parts from a VW dealer?


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## peepsRawsome (Jan 13, 2009)

No codes pending or present 
Yes from heritage I installed the maf, cat and o2's


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## peepsRawsome (Jan 13, 2009)

This morning it has power and runs smooth again


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## peepsRawsome (Jan 13, 2009)

You think the transmission might have something to do with it? It's an automatic


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## Anony00GT (Mar 6, 2002)

It may, but that's impossible to determine over the interwebs.


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## corymnr (Jun 2, 2008)

97 aba swap to a 91 jetta gl, and i have the same thing going here

tt 268 cam, matching chip, obx header, 2.25 tt ss exhaust cold idle isnt wortha crap once warm does fine, installed dorman 42002 spark plug non foulers, which got rid of the flat spot when accelerating, diagnostic testing for p0422 shows that the front sensor took a dump,


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## Anony00GT (Mar 6, 2002)

corymnr said:


> 97 aba swap to a 91 jetta gl, and i have the same thing going here
> 
> tt 268 cam, matching chip, obx header, 2.25 tt ss exhaust cold idle isnt wortha crap once warm does fine, installed dorman 42002 spark plug non foulers, which got rid of the flat spot when accelerating, diagnostic testing for p0422 shows that the front sensor took a dump,


 Start your own thread please. That way we don't get confused.


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## Lah2211 (Dec 17, 2012)

*Values for the o2*

What range of values do you look on the o2's for diagnostics to determine the cat isnt operating properly? and can it be getting a bad reading when the maf is dirty. ive seen some threads on having to clean or replace the maf to eliminate the p0422, i have the same dtc and been trying to eliminate it.


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## Lah2211 (Dec 17, 2012)

sorry bout values on the o2s didnt read the whole thread first


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## Anony00GT (Mar 6, 2002)

Lah2211 said:


> What range of values do you look on the o2's for diagnostics to determine the cat isnt operating properly? and can it be getting a bad reading when the maf is dirty. ive seen some threads on having to clean or replace the maf to eliminate the p0422, i have the same dtc and been trying to eliminate it.


Yes a bad MAF can cause fuel trim issues resulting in false cat codes, even with lack of trimming codes.

However, driving for an extended period of time without repairing the issue can eventually kill the cat.


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