2013 Tahoe will not pass emissions

[dan_erickson]

I picked up a 2013 Tahoe 5.3L with 150,000 miles and I am having a hell of a time with emissions. I had a check engine light on for P0172 and P0175, running rich on both banks. I had that looked at the the fuel composition was read way rich that the computer was reset. Engine light has been off since then.
I have taken the truck in for emissions so I can plate it and I keep getting failed for catalyst monitor not ready. My drive to work is all city so I assumed that was the issue and took the Tahoe out for a couple long drives over the weekend. Still failed. There was a tech at the emissions site that plugged the scanner in and he said that I am still running really rich, 21% actually. He reset the fuel trims, and also gave me some information that there is a pending MAP sensor code.
What are some other common issues to look at with these GM trucks? I don’t want to start the parts cannon at this thing.

 

[Chris142]

It likely wont run the cat monitor when the cats are getting flooded with fuel. Leaky injector? Does it have a fuel pressure regulator on the intake?

 

[Malo83]

 

[sloinker]

If there is a trusted garage you use, take it there. Fuel injector(s), MAF/MAP sensors, O2 Sensors, the converters themselves....you need a good tool to read, map and graph all the variables before you start throwing parts at it.

 

[i6pwr]

What is the service history? Have the plugs been changed and if so, did you use the AC Delco plugs or an aftermarket plug like a Bosch Platinum 4? These engines like the OE Delco iridium plugs, if original, I would change them.

The upstream O2 sensors get lazy after awhile, if original, I would surely change the upstream sensors but would like to see their data first, should be a rapid sine-wave and not a lazy line all over the place.

I would also clean the MAF meter but only use MAF cleaner. Some people just replace them after 150K but don't always have to.

Are you using a K&N filter? If so, the oil can contaminate the MAF over time and require cleaning.

If the MAF is dirty, the PCM thinks the airflow is higher and adds more fuel...I'm almost positive that's correct.

So if that were mine, I would first start with the MAP sensor and verify it's working properly. If the plugs are old, I would replace the plugs with OE AC Delco iridiums, clean the MAF, check for any vacuum leaks.

The PCM throws codes when one sensor is out of range, and could be caused by another sensor causing it to vary wildly.

The MAF meter measures airflow and the small wires inside are cooled by the airflow and change the resistance.

This is a shot in the dark but an idea on what's possibly going on.

You could have a dirty MAF meter, and your throttle input doesn't jive with all the added airflow the PCM thinks it's getting, then compares that to the MAP (Manifold Pressure) sensor and says....."hey, what's going on here? I have lower than normal manifold pressure (small throttle opening to see less atmospheric pressure) for the amount of airflow I'm getting (dirty MAF) and with little throttle input, my MAP should be low and the airflow should be low, but my airflow is high and my MAP is low"

So it may just decide to throw a MAP CEL instead of a MAF CEL.

That doesn't mean that's what's going on, but gives an insight on how one sensor affects another.

Sorry to get long-winded, but hope that helps.

 

[dan_erickson]

What is the service history? Have the plugs been changed and if so, did you use the AC Delco plugs or an aftermarket plug like a Bosch Platinum 4? These engines like the OE Delco iridium plugs, if original, I would change them.

The upstream O2 sensors get lazy after awhile, if original, I would surely change the upstream sensors but would like to see their data first, should be a rapid sine-wave and not a lazy line all over the place.

I would also clean the MAF meter but only use MAF cleaner. Some people just replace them after 150K but don't always have to.

Are you using a K&N filter? If so, the oil can contaminate the MAF over time and require cleaning.

If the MAF is dirty, the PCM thinks the airflow is higher and adds more fuel...I'm almost positive that's correct.

So if that were mine, I would first start with the MAP sensor and verify it's working properly. If the plugs are old, I would replace the plugs with OE AC Delco iridiums, clean the MAF, check for any vacuum leaks.

The PCM throws codes when one sensor is out of range, and could be caused by another sensor causing it to vary wildly.

The MAF meter measures airflow and the small wires inside are cooled by the airflow and change the resistance.

This is a shot in the dark but an idea on what's possibly going on.

You could have a dirty MAF meter, and your throttle input doesn't jive with all the added airflow the PCM thinks it's getting, then compares that to the MAP (Manifold Pressure) sensor and says....."hey, what's going on here? I have lower than normal manifold pressure (small throttle opening to see less atmospheric pressure) for the amount of airflow I'm getting (dirty MAF) and with little throttle input, my MAP should be low and the airflow should be low, but my airflow is high and my MAP is low"

So it may just decide to throw a MAP CEL instead of a MAF CEL.

That doesn't mean that's what's going on, but gives an insight on how one sensor affects another.

Sorry to get long-winded, but hope that helps.

That helps a lot and I’m going to try to clean the MAF sensor first and see what happened. Plugs and 02 sensor may be original. I really do not know.

 

[i6pwr]

If the plugs are original I would definitely add them to the list, you could pull one and check.

 

[spasm3]

Is the thing getting up to temp? An open thermostat/running cold may make it run rich.

Need to go through everything. Plugs, wires, clean the MAF, if o2 sensors are original, I'd replace.

And as suggested above, you may need a shop with software to see what is happening.

 

[dan_erickson]

I wish I had a better scanner so read all the sensors. From what I can tell the ECT is reading properly. The IAT is reading properly. Last last night I pulled the MAF and it was very dirty with a brown coating on the filament. I cleaned it and reinstalled and also changed the air filter.
I’d like to do the plugs and O2 sensors because I have no clue the history on those items

 

[atikovi]

I picked up a 2013 Tahoe 5.3L with 150,000 miles and I am having a hell of a time with emissions.

Private sale or dealer? Was the check engine light on when you looked at it or did they turn it off?

He reset the fuel trims, and also gave me some information that there is a pending MAP sensor code.

What do you mean "he reset the fuel trims"? If he cleared the Check Engine light, the on-board monitors will have to run again to completion each time that is done in order to pass. That could take another 50-100 miles or more.

 

[repairman54]

I replaced the front (position 1) O2 sensors on my '11 5.3 Tahoe and got 2 mpg back. OEM sensors had 100k miles on them, scanned OK with no codes.