Fault: 16805 - Warm Up Catalyst: Bank 1: Efficiency Below Threshold

[mad70sx]

16805 - Warm Up Catalyst: Bank 1: Efficiency Below Threshold
P0421 - 001 - Upper Limit Exceeded - Intermittent

Hey guys.

This fault code has popped up a few times since putting on a full F.I. exhaust. Pops back up a couple of days after clearing it.

I searched the forums on this fault code,indicating it is O2 sensor related,correct? I assume O2 spacer will be needed. Which sensor(s) does this fault code point to? Should I just put a spacer on all 4? Is one spacer as good as the next? Any spacer in particular that you guys would recommend?

Thanks.

[kerlow66]

I had a F.I set up too with revo stage 1 chip and got the oxygen spacers,And still got the same codes as you do ,i will clear it with a vag and it will show up again about 50miles or so,then called revo and they told me to get a stage 2 chip which i did and it cleared the codes for good.

[mad70sx]

Bump

Anyone else care to comment?

[buck_dat]

Sounds like the answer is to spend more Money?

[durrmcdanks]

You only need spacers for the back o2 sensors(after the cats). The rear o2 sensors are responsible for reading the rate at which the air flows through the pipes. When the cats are taken out or are different (High flow cats) the air flow increases tripping the fault code because the velocity of the gas has increases which the ECU is not programmed for.

You have two options:
1. jhm tune which would re programs the ECU to accept that change, but you need piggie pipes with this tune. Totally worth it haha.
2. 02 sensor spacers for the rear O2 sensors from VAST

[mad70sx]

You only need spacers for the back o2 sensors(after the cats). The rear o2 sensors are responsible for reading the rate at which the air flows through the pipes. When the cats are taken out or are different (High flow cats) the air flow increases tripping the fault code because the velocity of the gas has increases which the ECU is not programmed for.

You have two options:
1. jhm tune which would re programs the ECU to accept that change, but you need piggie pipes with this tune. Totally worth it haha.
2. 02 sensor spacers for the rear O2 sensors from VAST

Awesome! This is the kind of info I'm looking for.

I already have the F.I. dp's. I don't want to mess with the ECU until the CPO runs out. I desperatly want a JHM tune but I checked with the dealership that I go to and they said any aftermarket ECU tune will void the CPO. Any aftermarket ECU except a Stasis tune,that is. So happens this dealership reps Stasis also. Fucking hypocrates!

Looks like a set of spacers from VAST will soon be on order.


Thanks.

[dparm]

Efficiency below threshold means the difference in values between the pre-cat and post-cat O2 sensors is incorrect. Specifically, it means that the post-cat O2 sensor thinks the cat converter is not doing its job.

I'm surprised a catback exhaust would do this. Typically you see this at random with certain high-flow cats. They're right at the limit of what's legal for smog, and the sensor occasionally trips the light.

[drew]

Efficiency below threshold means the difference in values between the pre-cat and post-cat O2 sensors is incorrect. Specifically, it means that the post-cat O2 sensor thinks the cat converter is not doing its job.

I'm surprised a catback exhaust would do this. Typically you see this at random with certain high-flow cats. They're right at the limit of what's legal for smog, and the sensor occasionally trips the light.

lol...he has high flow cats

[dparm]

Well, in that case...no surprise. It can be pretty sporadic. I'd clear the code and see how quickly it comes back.

An untuned motor running aftermarket downpipes, cats, etc. will tend to detonate some unspent fuel in the catalyst. The substrate will weaken over time.