Persistent O2 code

[lanceinsb]

I have a 2013 ZL1 / manual with 12,000 miles. Bought it with 5000 miles from a Chevy dealer out of state who told me it was dead stock. About every 600 miles or less I get an engine code for the O2 sensor saying the car is running rich. To date, the local dealer has replaced the injectors, all O2 sensors, MAF - and it still throws the code. This visit the dealer discovered the resonators had been removed, but camouflaged to look like they are there. I am being told that the car will continue to throw the code until the resonators are replaced - at my cost, of course ( I will take this up with the dealer who sold me the car). My questions are: 1) would the resonators being gone cause the car to run rich enough to continually throw a code, and 2) If I do replace the resonators, and the car continues to throw the code, does anyone have an idea of what this could be? 3) Anybody else had a similar problem, and how was it resolved with GM?

Sorry for the long post, but at this point I think they are lost and just throwing parts at it.

[jayno20]

Not resonators per se, but catalytic converters. If they are removed the car will DEFINITELY throw an O2 code (need to know the exactly code you are getting to verify) but if that is the case replacing the cats will eliminate the problem with the code.

[frankwjr]

or get it tuned...dynoSteve! It would be a MASSIVE improvement in your case...

[E. Bryant]

If the cats are punched out, you will indeed get codes - but those DTCs are different than what would lead a technician to believe that the car was running too rich. Can you go back to your paperwork and confirm what DTCs are being set?

[Batmanntexas]

Not having catalytic converters might cause a RICH DTC, but you would need someway to be able to monitor your STFT (short term fuel trims) to see if the computer was constantly adding fuel for the increased air flow.

If you were not aware just how it all works, the front two O2 sensors (Bank 1 Sensor 1, Bank 2 Sensor 1) are monitoring for STOICH AFR, i.e. they control the fueling of the motor, and are only in play during CLOSED LOOP operation, meaning they are cutout of the system at WOT or OPEN LOOP, depending on how your tune is configured. The second set of O2 sensors (Bank 1 Sensor 2, Bank 2 Sensor 2) are predominantly there to monitor catalytic converter efficiency/operation, however they also play a role in determining rich/lean condition as well. There is nothing that monitors whether you have resonators or mufflers or don't have them.

If a mechanic told me that not having resonators was causing my RICH DTC, I'd find another mechanic in a hurry. A resonator is a hollow tube of a certain length and diameter, engineered specifically to cancel out those resonant frequencies that would otherwise cause excessive drone within the car. They have a negligible effect on exhaust gas flow.

From your initial post, what the Dealer is calling the resonator, sounds like the actual catalytic converter. A lot of Forced Induction guys, myself included, have hollowed out the catalytic converter so as to not cause problems down the road, yet give the visual appearance that they are still in place.

If that is indeed the case, you will definitely need a tune to get rid of the CEL. If done properly, it will still pass an ODBII Emissions test, unless they take a tailpipe sample.

-Scott

[lanceinsb]

Originally Posted by Batmanntexas

Not having catalytic converters might cause a RICH DTC, but you would need someway to be able to monitor your STFT (short term fuel trims) to see if the computer was constantly adding fuel for the increased air flow.

If you were not aware just how it all works, the front two O2 sensors (Bank 1 Sensor 1, Bank 2 Sensor 1) are monitoring for STOICH AFR, i.e. they control the fueling of the motor, and are only in play during CLOSED LOOP operation, meaning they are cutout of the system at WOT or OPEN LOOP, depending on how your tune is configured. The second set of O2 sensors (Bank 1 Sensor 2, Bank 2 Sensor 2) are predominantly there to monitor catalytic converter efficiency/operation, however they also play a role in determining rich/lean condition as well. There is nothing that monitors whether you have resonators or mufflers or don't have them.

If a mechanic told me that not having resonators was causing my RICH DTC, I'd find another mechanic in a hurry. A resonator is a hollow tube of a certain length and diameter, engineered specifically to cancel out those resonant frequencies that would otherwise cause excessive drone within the car. They have a negligible effect on exhaust gas flow.

From your initial post, what the Dealer is calling the resonator, sounds like the actual catalytic converter. A lot of Forced Induction guys, myself included, have hollowed out the catalytic converter so as to not cause problems down the road, yet give the visual appearance that they are still in place.

If that is indeed the case, you will definitely need a tune to get rid of the CEL. If done properly, it will still pass an ODBII Emissions test, unless they take a tailpipe sample.

-Scott

Thanks for the detailed description. Since my post, I have confirmed it IS the resonator that was modified/removed. The CATS are in place and functioning. My understanding of the resonator is as you described - a sound canceling device aft of the O2 sensors that should have no effect on their reading. I am going through my paperwork to find the exact code it is throwing - but I am repeatedly told it is the rear sensor on the right bank reading rich.

As for getting a different mechanic - I am on a rock in the middle of the Pacific, so my choices as long as its a warranty thing are limited!

Thanks again for taking the time to answer the post. It gives me a little more ammo as I deal with the service department on this thing.

[E. Bryant]

GM MAF cars are typically not going to set any rich or lean codes just because the mufflers were modified or deleted. Something else is going on with your car, and it might take a bit of datalogging with a scan tool during some road testing to figure out the issue. Certainly, just throwing parts at it isn't fixing the problem!

[lanceinsb]

Originally Posted by E. Bryant

If the cats are punched out, you will indeed get codes - but those DTCs are different than what would lead a technician to believe that the car was running too rich. Can you go back to your paperwork and confirm what DTCs are being set?

The code that keeps coming back is P015B. Does that make sense?

[jayno20]

Originally Posted by lanceinsb

The code that keeps coming back is P015B. Does that make sense?

Is that the only code? That code is "Oxygen Sensor Delayed Response" which would definitely be one of the ones coming up if cats aren't detected. I ran LTH without cats for a few months and there were 6 or so codes that kept coming up due to the cats being missing.

[SlingShot]

The ZL1 does not have resonators from the factory. If there were resonators, they would be located between the cats and mufflers.

[Batmanntexas]

Typically, I've seen the P015B code come up when long tube headers were installed. When I asked my previous tuner about it, he explained it like this:

when stock, injector A fires at X time. THe ECM expects to see the result of injector A at sensor 1 at time Y, thereby correlating injector pulsewidth injection time to STOICH.

when you add long tube headers, it throws the timing off between X and Y, resulting in the ECM setting code P015B.

Now, that seems to make sense to me, but I'm not an expert. Just sharing what I have been told, and what seems to make sense to me.

Not having catalytic converters, I would expect to see code P0420 or P0430.

BTW, P015B is a "Oxygen Sensor Delayed Response - Lean to Rich (Bank 1 Sensor 1)", which is a front O2 sensor, not a rear O2 sensor.

-Scott

[jayno20]

All of this info boils down to one of 2 things. Either get cats on the car, or get it tuned to eliminate that check engine light.

[camguynj]

Given you're certain you have cats and IF that's the only code then that IS NOT a running rich code. It's a delayed response code which indicates the O2 sensor is not functioning properly.

[ZO6 Bryan]

Idiot dealer just throwing parts at it. The problem is the driver side front(pre-cat) O2 sensor. They need to replace it. Long tube headers can cause this code because the sensor has been moved further from the engine. That is not the case for you. And that code has nothing to do with running rich. It means the O2 sensor is slow to react.

UNLESS
someone accidently swapped the Bank 1 sensor 1 with Bank 1 sensor 2.
Check it, the "square" O2 connector should be plugged into the O2 after the cat. The "flat" O2 connector should be plugged into the O2 closest to the engine.