Check Engine Light Question

[Joseph92]

Ok so the other day my check engine light came on and I went to auto zone to see what the code was. Well it is running lean. But my question is that after the guy pluged in the OBD2 scanner and read the codes and then unpluged the scanner WITHOUT CLEARING THE CODES. So we go inside and talk for a few minutes and then when I come out to leave I started the car the check engine light turned off. Why did this happen is it normal, are the codes still their so the dealer can see them?

[Smileybgh]

If he did not clear the codes, then the dealer will be able to retrive the History Codes with the scan tool. When a CEL comes on, it has a Freeze Frame that records inputs from certain sensors while the "fault" occured. Some codes turn off the CEL after it notes "3 Good Cylce Trips" which in your case, if it was running "lean", an O2 Sensor was probably not reading properly when it ran a self-test. Usually after 4 consecutive ignition cycles that the diagnostic runs (self-test) and does not fail, will be enough to turn off the CEL if the fault was an "erroneous" fault.:flag2:

[Joseph92]

Thank you so much for the info that is good to know.

[Joseph92]

Ok so I am posting back with an update.

So my check engine light keeps turning off and on still, and I do have a cold air intake but I had that all checked out and that is all good. The problem is that my long term fuel trims are in the positive 20%. What percent does it have to be at for the check engine light to turn it self back on?

The dealer suggests that I put the stock air box back on to see if the fuel trims go back to normal. And my new next question is what should the fuel trims be normally?

Thank you.

[2011 SS SLP ZL427]

I would install the original intake back on the car and see if it corrects itself these cars are to sensitive to do any simple modifications to them the best thing in my opinion is run them stock, with all the sensors and federal regulations on pollution the computers are running the fuel trims so tightly that any increase in air or fuel will cause a problem.

[Joseph92]

Originally Posted by 2011 SS SLP ZL427

I would install the original intake back on the car and see if it corrects itself these cars are to sensitive to do any simple modifications to them the best thing in my opinion is run them stock, with all the sensors and federal regulations on pollution the computers are running the fuel trims so tightly that any increase in air or fuel will cause a problem.

That is what I am going to do tomorrow. But I have had this cold air intake for over a year and a half now and it was about 4 weeks ago the lean code for bank 1 and 2 came on.

What should the fuel trims be at?

[2011 SS SLP ZL427]

The fuel trims are suppose to run very closely to a 14.7 to 1 ratio which means they want 14.7 parts of air mixed to 1 part of fuel, the government and automakers realize that this ratio is ideal for the best fuel burn and least amount of pollution coming out your tailpipe.

[Joseph92]

That is the fuel ratio I am just talking about the fuel trims.

[Darkweasel]

Fuel trims should be around 0% meaning the ECM doesn't have to richen or lean out the fuel injectors. A trim of 20% means the ECM is trying to increase the injector pulse width because the O2 sensors are reading lean. Many things can cause this and a CAI could cause an issue since more oxygen can enter the engine. But the trim sounds too extreme to be caused by that. Hope the info helps.

[firestone_ss]

fuel trims typically run +/- 3percent with no issues

[DJ_BigC]

These are all of the conditions that I know of that can cause a lean or rich code. These are the codes that usually set. P0171, P0172, P0174, P0175.

• Vacuum hoses for splits, kinks, and improper connections
• Insufficient fuel in the tank
• Low fuel pressure
• Fuel contamination
• Malfunctioning fuel injectors
• Missing, restricted, or leaking exhaust components, faulty HO2S readings, sensor
• Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
• The air induction system and the air intake ducts for leaks or for a missing filter element
• A cracked EVAP canister
• Evaporative pipes obstructed or leaking
• The crankcase ventilation system for leaks
• The air intake duct for being collapsed or restricted
• The air filter for being dirty or restricted
• Objects blocking the throttle body
• Excessive fuel in the crankcase
• The evaporative emissions control system for improper operation
• Missing, restricted, or leaking exhaust components
• Malfunctioning fuel injectors
• Fuel contamination

I usually see this code for bad fuel, but that's just me. I can't recall of the top of my head if this code sets for a CAI, but you never know. But at least i have a bit of info for you.

Long term fuel trims should be anywhere for -19/+19 at operating temp for ideal vehicle operation according to my diagnostic chart provided to me by GENERAL MOTORS. Short term fuel trim will also fluctuate with the HO2S readings and always change. A dealer should run a snapshot while road testing the vehicle to see when the code sets and what the ECM data looks like to pinpoint and find the exact problem. I also cant remember off the top of my head if the long term fuel trim can be reset and start from fresh to see exactly what its reading once the correct parameters are met to update that LTFT data.