Tuning out rear O2 / lambda sensors on 2006 Corvette

[GlosterVette]

Hi All, I wonder if you can help? I’ve recently fitted long-tube headers and x-pipe to my 2006 Corvette base. The headers have the upstream (pre-cat) O2 sensors, but there are no downstream (post-cat) O2 sensors. I’ve connected HP Tuners to the car via MPVI3 and switched off all the DTCs related to sensor 2.

Version 5 of HP Tuners software doesn’t have an option to disable Catalyst Test, or to disable Post O2 Test.
What do I need to do, to ensure that won’t be a problem?
Note that I have to use V5 because I’ve got MPIV3. I’m now aware that if I’d bought MPIV2, I could’ve got V4 software and those disable options would’ve been available.

Also, I’ve heard mention that I should leave the rear O2 sensors connected, but just tie them out the way. Is that required? Unfortunately I found that out after fitting the headers, so I’ve already cut the rear sensors away.
If they’re needed, does anyone know the correct GM or aftermarket part numbers I need to order for downstream LS2 O2 sensors? I’ve seen a load of conflicting information.

Sorry, that’s a lot of questions. To make this useful, here’s some helpful data for others going through the process…

In V5 of their software, HP Tuners require you to do a training course before you can amend the emissions-related DTCs. It’s not that big a deal, but once you’ve done it and loaded your completion code into VFM Editor, I found I had to restart the software and re-read the data from the car to be able to access the emissions DTCs. Here’s a link to the instructions about how to do it: Emissions – HPTuners Europe.

Here are the DTCs I switched off… P0036 P0054 P0056 P0060 P0137 P0138 P0140 P0141 P0157 P0158 P0160 P0161 P0420 P0430 P2A01 P2A04
I also switched off Catalyst over temperature protection.

 

[teamzr1]

What do you mean by "I’ve already cut the rear sensors away." ?

Or do you mean you disconnected them from the PCM wiring harness connectors for them ?
Did you also do away with the CATS ?

I always recommend that the S2 downstreams be installed into mid-pipes as they still have a purpose
Even my own 1999 C5 the CATS were replaced with the X-pipe in their place and S2 bungs were installed in the mid-pipes
so that the S2s were installed

Where you live, do they require SMOG testing ?

 

[GlosterVette]

Sorry, I should’ve clarified that point.

When I removed the original exhaust manifold, I couldn’t get the rear sensors out of the old manifold while it was still on the car - they were too badly seized. Reaching up to the harness, I couldn’t get my fingers around the locking tag on connector to free them at that end, so I cut the wires so that I could get the old exhaust manifold out. At that time, I wrongly assumed that I wouldn’t need them. The connectors are still on the PCM harness, so if required, I could plug new ones into the PCM harness.

When I fitted the long-tube headers and matching aftermarket X-pipe, it only has the fitting to mount the upstream (pre-cat) sensors, but no place for downstream (post-cat) sensors.

In fact, when I got the x-pipe, it didn’t have any cats, so I had a local exhaust fabricator modify the x-pipe to fit cats to it.

I’m based in England. We have an annual roadworthiness test that’s known as the MoT test. I’m familiar with the California smog test and I’d say that the UK test isn’t as restrictive on emissions as that. There are limits for emissions that the car must achieve (so the car will need cats and be running well to achieve it), but we don’t have the “modified with non-approved parts” limitations that California has. Essentially, the MoT test doesn’t specify how you achieve the emissions levels, you just have to achieve them. We must not have a check engine light showing, but we don’t have a test for diagnostic codes.

 

[Pinhead]

The biggest problem with the MOT and catalytic converters is that it is a visible check if it is newer than 1993 it must have one fitted
When I fitted long tubes to my 99 camaro and off road Y pipe I only needed the pre cat sensors but the wires wouldn't reach
So I re pinned the rear sensors to act as fronts instead of using extended harnesses

Then tuned the cats out using efi live

I have never used HP tuners so I cannot say how the layout works with that but often if something cannot be turned on or off in the tune you can set values required to implausible values so that they are ignored and dint set a light

 

[GlosterVette]

You’re correct, that’s the sort of thing that I’m looking to achieve. I need to get the car through its MoT, so I need to make sure the check engine light doesn’t come on.

I believe I’ve turned everything off, apart from the Catalyst Test and the Post O2 test, which can no longer be disabled on the HP Tuners software. So I’m wondering if there’s some other way to make sure those tests don’t trigger a check engine light. That’s why I’m wondering if getting new rear O2 sensors and plugging them in, but tying them out the way, will help in any way.

 

[Pinhead]

Can you set a value to trigger the mil to a value that would never be acheaved with the unplugged sensors

 

[GlosterVette]

Thanks for your reply. I see what you mean. I think that will be the answer, but I don’t know what the PCM is expecting to see when it carries out the catalyst test or the rear O2 test. I don’t know if the DTCs that I’ve switched off so far will be enough. Logically I would expect those tests to fail if there’s no rear O2 sensor.

I know what the next question is going to be… why not try it!

I can’t take the car for a drive because I’ve got no MoT. The only thing I can do is pull the car onto the driveway and run it for a while. Does anyone know if there’s a specific thing that triggers to catalyst test or rear O2 test?

 

[Pinhead]

I had no cats on the camaro
There is always a way

 

[Pinhead]

I should imagine just running it should trigger it if disconnected
It may need to see a faliure over 2 drive cycles to trigger
Sorry I can't be more help at the moment as I just can't remember
If no one else chimes in I can get my tuning laptop out and see if I can remember what I did at the weekend

 

[GlosterVette]

I had no cats on the camaro
There is always a way

Ha ha ha!!! Brilliant

 

[GlosterVette]

I should imagine just running it should trigger it if disconnected
It may need to see a faliure over 2 drive cycles to trigger
Sorry I can't be more help at the moment as I just can't remember
If no one else chimes in I can get my tuning laptop out and see if I can remember what I did at the weekend

That’s very interesting, thank you

 

[teamzr1]

Before doing anything else with the changes, you have flashed in
Drive the car to get some valid drive cycles on it and then with the Hptuners is look at what I/M SMOG readings are
This gives you a clear idea what on-board SMOG tests are in a complete/passed or non-complete/failed state
Also record and see what the long and short fuel trims values across the engine's RPM, load and MAP and see if
Values are balanced B1/B2 ( left/right heads) and how close to zero those values are
Larger the positive values are the leaner O2s are reporting AFR and the more negative values are means richer AFR is

Those that non-complete see what functions they are and then determine how to correct that
Do NOT leave those cut S2 O2s wires hanging in the wind as they can pick up either EMI or RFI and back feed to the PCM
causing problems
You could, if need be, install new S2s to plug into the PCM wiring harness for them and being they have heaters do not place
them to close to something that might transfer that O2s heat

The S2s are not just for monitoring the CATs, GM uses them on startup to determine what the average fuel injector ON time will be
for each drive cycle
PCM uses S2s for this as the S1a are not stable enough as the SMOG pump is injecting air into both exhaust streams effecting S1s and the CATs

If having no S2s than AFR/fuel trims can be incorrect and workaround by tuning PCM as to MAF, VE and commanding injectors flow

I dislike both HPtuners and Efilive, both groups were hackers in the 1990s, I knew them well
Both really come from aussie land
I dislike how greedy they are wanting customers left nut to keep paying them so-called credits/licenses per PCM and TCMs

Tuning tool I use for all my tuning customers does not do that crap

I just looked at version 5 of Hptruners, I suspect the feds here wacked them for smog violations practices
so they locked any smog function as a default and force customers to have to screw around with Hptuners to unlock those
But I never see that with older versions of their VCM editor software

 

[GlosterVette]

Before doing anything else with the changes, you have flashed in
Drive the car to get some valid drive cycles on it and then with the Hptuners is look at what I/M SMOG readings are
This gives you a clear idea what on-board SMOG tests are in a complete/passed or non-complete/failed state
Also record and see what the long and short fuel trims values across the engine's RPM, load and MAP and see if
Values are balanced B1/B2 ( left/right heads) and how close to zero those values are
Larger the positive values are the leaner O2s are reporting AFR and the more negative values are means richer AFR is

Those that non-complete see what functions they are and then determine how to correct that
Do NOT leave those cut S2 O2s wires hanging in the wind as they can pick up either EMI or RFI and back feed to the PCM
causing problems
You could, if need be, install new S2s to plug into the PCM wiring harness for them and being they have heaters do not place
them to close to something that might transfer that O2s heat

The S2s are not just for monitoring the CATs, GM uses them on startup to determine what the average fuel injector ON time will be
for each drive cycle
PCM uses S2s for this as the S1a are not stable enough as the SMOG pump is injecting air into both exhaust streams effecting S1s and the CATs

If having no S2s than AFR/fuel trims can be incorrect and workaround by tuning PCM as to MAF, VE and commanding injectors flow

I dislike both HPtuners and Efilive, both groups were hackers in the 1990s, I knew them well
Both really come from aussie land
I dislike how greedy they are wanting customers left nut to keep paying them so-called credits/licenses per PCM and TCMs

Tuning tool I use for all my tuning customers does not do that crap

I just looked at version 5 of Hptruners, I suspect the feds here wacked them for smog violations practices
so they locked any smog function as a default and force customers to have to screw around with Hptuners to unlock those
But I never see that with older versions of their VCM editor software

View attachment 25794

That’s really good advice and help. Thank you very much. I’ll pull the car out onto the driveway and will try those things.

That’s a very good point about not leaving the PCM harness connectors unterminated. I might have to go and order 2 more so that I’ve got the correct termination. Do you know what the correct GM part numbers should be for rear O2 sensors on a 2006 model? I’ve been looking that up and I’m getting lots of conflicting information.

Sorry for so many questions, but do you know approximately how hot the sensors get when the heater gets going? That’s a very good point that you’ve made!!!

I know what you mean with the HP Tuners costs. I wish that wasn’t the case, but I’ve just accepted that tuning’s expensive and that’s what it costs to play. And yes, I’m sure you’re 100% correct that they’ve had a visit from some government department, and V5 is the best they’ve been able to do after the input from the lawyers! After doing the course, those DTCs are unlocked, but annoyingly they’ve removed the disable button for those two tests.

Thanks again for all the advice, I really appreciate it. I’ll give it a try at the weekend and will update here.

 

[teamzr1]

You can look at these from Amazon

Amazon.com

 

[teamzr1]

That’s really good advice and help. Thank you very much. I’ll pull the car out onto the driveway and will try those things.

That’s a very good point about not leaving the PCM harness connectors unterminated. I might have to go and order 2 more so that I’ve got the correct termination. Do you know what the correct GM part numbers should be for rear O2 sensors on a 2006 model? I’ve been looking that up and I’m getting lots of conflicting information.

Sorry for so many questions, but do you know approximately how hot the sensors get when the heater gets going? That’s a very good point that you’ve made!!!

I know what you mean with the HP Tuners costs. I wish that wasn’t the case, but I’ve just accepted that tuning’s expensive and that’s what it costs to play. And yes, I’m sure you’re 100% correct that they’ve had a visit from some government department, and V5 is the best they’ve been able to do after the input from the lawyers! After doing the course, those DTCs are unlocked, but annoyingly they’ve removed the disable button for those two tests.

Thanks again for all the advice, I really appreciate it. I’ll give it a try at the weekend and will update here.

The O2 sensors are getting 12 volts from the fuse panel, has its own fuse
The heater then is on as long as ign key is on, I do not know how hot it would be to the outer part of the O2 tip
But suspect not being in the exhaust stream if not installing them, maybe less than 100 F deg ?

Kinda stupid of HPtuners such as stating in 2019 GM began locking up the PCM so they could not be tuned
but HPtuners charges $1,500 where 2019–2023 vehicles have to mail the PCM to HPtuners and they hack out
the Global B internals so the owners pay that, the shipping and time costs plus special HPtuners prices for the VCM
to be able to hack and tune PCM :-(

Back to the above, if via the HPtuners it shows all I/M tests complete and no check engine light on, should be good
And again check your fuel trims to see without rear S2s function if the trims are too lean or rich

 

[GlosterVette]

Thank you very much for all your help and advice, I really appreciate it.

I’ll try running the car at the weekend and will make the checks you’ve advised.

 

[GlosterVette]

I got a break in the rain and decided to take the car onto the driveway and see how the changes affected things. I could only take it onto the driveway because I can't take it onto a public highway until I've got a valid MoT (or during my journey to/from the MoT test). Please bear in mind that it hasn't run for a few weeks, so I'm sure there's an element of it needing a bit of an "Italian tune-up"... the car felt a little bit lumpy compared to how it normally runs.

Anyway, the best news is that there was no check engine light. I'm not sure if it will stay that way. I guess that only time will tell.

Here's a screenshot of the diagnostics...


I'm guessing the two tests of the oxygen sensor are the ones that could trigger an engine light. However, they didn't trigger during the whole time I had the car running.

I did some logging on the car, as per your suggestion. In this image, I have run the first half of the test at tickover, then the second half at 2000 rpm. How does that look?


Here's a zoom into those charts...



And here's the data when it's just at tickover...



And a zoom of the graph at tickover...



Sorry this is in metric instead of imperial. I'm new to HP Tuners and although I clicked the button to select imperial units, it just wouldn't make the change. Maybe I didn't restart the software enough.

I'll be interested to get your input. Like I say, if this looks like the car just needs a bit of a run to blow out a bit of muck, then that's something I'll be able to do once I've got it through the MoT.

 

[teamzr1]

What does "tickover" mean ?

So we see that 3 of the on-board I/M smog tests for O2s are in an incomplete state
Really need some longer drivecycle scanner recording to see if those go complete or not

Also need to see if those DTCs that have tripped age out or stay current as to some issues or not
The screen prints do not tell me a lot of detail
Best is to email me the scanner recordings and both the stock GM flash and yours, so I can do a compare
as if set correctly, those I/M tests should have gone complete on first startup

Email that directly to me at email: jr@teamzr1.com

 

[GlosterVette]

Thanks so much for your help with this, I really appreciate it. I'll send an email now.

Sorry, "tickover" is a British term for when a car is at idle.

 

[teamzr1]

Posting here as others may have an interest and following your post thread

I looked at the DTCs tables and you did set them correctly
Just follow the correct process wanted

SES Enable

Checking this box enables the display of the SES/Check Engine/Service Vehicle Soon lamp when this DTC occurs.
Unchecking this box disables the lamp.
NOTE: In some regions, emissions testing will fail automatically if monitoring for emissions-related faults is disabled.

Error Mode
The option selected in this dropdown specifies whether the MIL is lit for this DTC and whether the error is reported.

￭

MIL on First Error. Illuminates the MIL the first time the error is detected. This is appropriate for emissions-related faults that should be reported immediately.

￭

MIL on Second Error. Illuminates the MIL if the fault is active for 2 consecutive driving cycles. This is appropriate for emissions-related faults that should trigger the MIL if they are detected consistently, but should NOT trigger the MIL when they are detected infrequently.

￭

No MIL Light. The MIL will not be illuminated for this fault, but the SERVICE lamp will be illuminated. This is appropriate for non-emissions-related faults that should be reported to the driver.

￭

No Error Reported. Neither the MIL nor the SERVICE lamp will be illuminated for this fault. This is appropriate for non-emissions related faults that should not be reported to the driver.

Clearly HPtuners got their tits caught in ringer with the feds EPA as I see they added this content, that older versions did not have
plus, they're adding the process you had to go through to allow making the changes



I analyzed what scanner recordings you emailed to me
Which is very limited as only did idle recordings
Took the data and worked it within Excel

Fuel trims are off, for idle only and when ECT as at normal temps
O2s B1/B1 S1 report lean (under around 0.500 mVolts), so PCM is commanding injectors on longer and hence
fuel trims reporting up to -5% rich and a bit of imbalance B1/B2 (right/left heads)

You cannot do all you want by idle only, you do not want to be caught with your pants down going in for your checks and Smog and than find after driving there the car fails
Need to find a time, place or maybe at night if in fear cops pull you over but need good scanner recording of a decent 10-15 miles testrun
and using many different engine modes as to load, RPMs and torque

You need to add the fuel trim cells PID, along with the fuel injectors ON time for both B1/B2 and also engine torque PIDs