Check engine light

[Greg2019]

I have 2008 chevy tahoe code po172 po175 on. Have had multiple scanners check out possibilities but no symptoms of bad fuel injector or o2 sensors bad. No misfire detected. Everything points to o2 sensor according to scanner. Have allready replaced last year.  Should I replace denso sensors with ac delco? 

[CamGTP]

It seems that having both banks show a rich code at the same time is going to point to something else. It's not likely for them to both fail and show that code.

 

If your scan tool is fancy enough see if you can pull up the alcohol content or ethanol content percent that the computer thinks is in the tank. Those year trucks run a virtual sensor that uses the fuel trims and isn't that accurate. Sometimes it can go off the rails and report a much higher content number than what is actually in the tank, causing the engine to use extra fuel for no reason.

 

So say you are running just regular pump gas like everyone else, most stations are up to 10% alcohol content. But your content "sensor" is reporting something like 30% or 50%, that is a sign of an issue and that would need to be reset.

 

 

[Greg2019]

Thank you I have seen that on you tube once. I sometimes tend not to fill up all the time. I will ask to see if I can use a newer scanner to check alcohol content.

[Ianf]

If it is running rich then you have an air starvation issue. Did you check the air filter for restrictions and also clean the MAF sensor with the proper cleaner. If the alcohol content was wrong then it would be running lean and add more fuel to compensate throwing codes P0171 and P0174. Low fuel pressure can also cause this to a certain extent but is not very likely. An exhaust leak could alos show these symptoms. Check the long term fuel trims and that might point you in the correct direction.

[Greg2019]

The short term and long trims are good. The only thing we could not find was why when could start the rpms start at 1300 and gradually go down to 1000rpm. This happens in about 30 to 60 seconds.

[Greg2019]

I must apologize,  I was wrong about the cold start idle.  Cold start idle is at about 1300 rpm and then settle down to 500 rpm in about 30 seconds.sometimes 60seconds. 

[bg1988]

On 9/24/2019 at 11:20 AM, Greg2019 said:

I have 2008 chevy tahoe code po172 po175 on. Have had multiple scanners check out possibilities but no symptoms of bad fuel injector or o2 sensors bad. No misfire detected. Everything points to o2 sensor according to scanner. Have allready replaced last year.  Should I replace denso sensors with ac delco? 

if the sensor failed you would have gotten a P0420/p0430 and would show 0.00 volts

 

 

for your code i would look at the MAF  might need to be cleaned

Edited October 2, 2019 by bg1988

[jay webb]

p0420 or p0430 is related to the converters. not the o2 sensors.