today my ses light came on for about an hour parked truck came out and started it it was off.. when light was on truck was running normal rpms temp shifting etc.. i have an appointment set up to have it scanned on thursday but if light isnt on will it be a waste of time?

today my ses light came on for about an hour parked truck came out and started it it was off.. when light was on truck was running normal rpms temp shifting etc.. i have an appointment set up to have it scanned on thursday but if light isnt on will it be a waste of time?
If the SES light is illuminated, the PCM will store a code in history.
If the light goes out, the code is still stored and can be read

thanks

99 tahoe ses light was on went off still had it scanned and the stored code was P0171 fuel bank 1 lean.. can anyone help i dont know where i should start? light came back on 1 mile after i left from having it scanned THANKS

99 tahoe ses light was on went off still had it scanned and the stored code was P0171 fuel bank 1 lean.. can anyone help i dont know where i should start? light came back on 1 mile after i left from having it scanned THANKS
P0171 indicates that the PCM has seen and tried compensating for a lean condition on bank 1.
If the PCM cannot adjust fuel trims to compensate for the lean condition, the code will set.
Some things to check are:
Bank 1 exhaust for leaks.
Bank 1 HO2S 1 is installed securely and the electrical connector is not contacting the exhaust system or ignition wires.
Any vacuum leaks that will only effect bank 1.
Also since this engine has Central Sequential Fuel Injection there is the possibility of a stuck injector poppet causing the condition.

the o2 sensors are all secure and wires are not touching exhaust or other wires, i couldnt find a exhaust leak or find a vaccuum leak i did it buy look and ear and touch.. i dont know how to check the injectors for a stuck poppet? should i change out o2 sensor? im also getting 6 1/2 mpg it holds a idle at 650 doesnt go up or down it idels smooth no missing runs and drives great except for fuel consumption and ses light

ttt help!

you will need to do an injector balance test to check the flow of the injectors.
TO clean and unstick the poppets you will need high pressure nitrogen and some specific tools

is this something i can perform myself? is there a manual i should go buy? shouldnt the injector throw a code or run rough if an injector was clogged? sorry for all the what if's im just getting frustrared with this truck!!!!

is this something i can perform myself? is there a manual i should go buy? shouldnt the injector throw a code or run rough if an injector was clogged? sorry for all the what if's im just getting frustrared with this truck!!!!

Unfortunately you are entering the world of professional intervention.
Your local Chevy or GMC dealer has the special tools to perform the unsticking procedure.
If you don't want to go that route, you can purchase an updated injector unit that will take care of the problem.

Many times with this system, you will not feel any difference when the poppets clog..typically you will get a cold misfire or rough running condition for a few seconds..possibly a SES light and code for a misfire if it is severe enough.

Unfortunately you are entering the world of professional intervention.
Your local Chevy or GMC dealer has the special tools to perform the unsticking procedure.
If you don't want to go that route, you can purchase an updated injector unit that will take care of the problem.

Many times with this system, you will not feel any difference when the poppets clog..typically you will get a cold misfire or rough running condition for a few seconds..possibly a SES light and code for a misfire if it is severe enough.
when you say injector unit do you mean injectors? what route would be best? and wich would be cheaper cheaper?

when you say injector unit do you mean injectors? what route would be best? and wich would be cheaper cheaper?
Usually the unsticking procedure is cheaper (unless one poppet will not unstick)..then you will have to purchase the injection unit.
For a DIY repair, I would buy the unit...but first verify the poppets are stuck with an injector balance test