Check Engine light-2003 Yukon XL

Most fuels now may or may not have ethanol but it could have up to 10% of ethanol in gas as stated on the pump dispenser. So you should be ok

2003 GMC Yukon XL check engine light run - YouTube

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www.youtube.com/watch?v=Rt06jXNGJT0
Mar 31, 2014 - Uploaded by Antonio Salinas
2003 GMC Yukon XL with a check engine light on. ... HOW TORESET CHECK ENGINE LIGHT, FREE EASY ...

May need a new alternator

Check all fuses in your power box. Sounds like could be electrical short. Check connections and grounds to alternator and starter and battery. Also check coils, plugs etc.

Once resolved, try a can of SeaFoam from Canadian tire $12.00..put half in a full tank of gas and the other half in your oil. Do this when the engine is warm, not hot. Let it sit for 30 minutes then take it for a 10 minute drive and see the difference. Save hundreds in injector flushing. This should alleviate the hard starts.cheers.

C0550 is the code for the ABS module. It is on the frame under the vehicle around the drivers door area. It is a module with all the brake lines coming from it. Reset the trouble codes and see if the problem returns. If it does, the module is not serviceable and will need to be replaced.

YOUR CAR IS IN THEFT SECURITY MODE.TRY USING DIFFERENT KEY.IF ANOTHER KEY DONT WORK.YOU HAVE PROBLEM IN THE SWITCH AND BCM.TO GET CAR TO STARTED TURN THE IGNITION WITH KEY IN TO ON POSITION WITH ENGINE OFF FOR 10 MINUTES.WATCH THE PADLOCK.IF IT TURNS OFF.TURN OFF IGNITION SWITCH FOR 5 SECONDS.THEN TRY TO START ENGINE.IF ENGINE STARTED PROBLEM IS IN THE IGNITION SWITCH AND BCM.IF YOU GET VECHICLE RUNNING NOT SAFE TO DRIVE BECAUSE THE VECHICLE WILL GO IN THEFT MODE SHUT OFF YOUR FUEL PUMP WHILE YOU ARE DRIVING IN HEAVY TRAFFIC. DONT LET GO GET IT FIX FOR YOUR AND FAMILY SAFETY.

the check engine light means you have a trouble code in your vehicles computer. After fixing the problem with the yukon the check engine light can be reset sometimes by disconnecting the battery and disconnecting the ECM fuse. Although some parts stores are known to check your codes for free they might also clear them with a scan tool.

it sounds like the fuel pump might have died, or blew fuse or relay see if it gets fuel at the motor

dear sir the flashing check engine light means the truck was misfiring at the time of the incident .If the light is still on you can go to auto zone they will pull the codes for you and reset the light if you like.but if running good now then probably nothing to worry about .

I had the same issue with another GM and never got it resolved except by replacing the battery.
Finally put it one that keeps good voltage while park or running.
Wall mart sells a $20 alternator and battery checking device you plug into a power socket.
Its digital read out is better for my eyes than the dash board one and has idiot color codes red yellow and green,

Some batteries seem to get shorted cells and that lower voltage can lead to engine shutdown even while driving. You would think a good alternator would keep the engine running but these new low rpm designs with heavy load...

This is all experience and I do not claim to be a GM tech.