CEL and Reduced Engine Power/ Won't do anything now

stephenclark4 · July 14, 2020

Here's a long one, so bear with me, please.

I have a 2003 Silverado 2500 HD with the 6.0 liter gas engine. I've lived with the flashing CEL at speeds above 60 mph for 3 years. Last year it started doing it at about 40 mph when I'm pulling my camper. My mechanic says it's a misfire and let's it go. Until this past weekend, it hasn't left me stranded.

On Saturday, I drove it for about an hour, parked in my driveway and left it running. When I went to leave I saw the CEL on solid and the DIC displaying the reduced engine power error. I turned it off, cycled the ignition a couple of times, and the error went away, but the CEL stayed on. I decided to leave it at the house and work on it later. On Sunday, a friend pulled the 0300 code on the scanner, but the truck ran fine, so we cleared it thinking it might just need some fuel cleaner ran through it.

I added some Seafoam on Monday and started to leave the house. 100 yards down the road the DIC flashes "Service Brake System" and immediately clears the error. I drove it about 5 miles, parked it for a couple of hours, then started to drive home. I stopped by the store on my way home and the doors unlocked as I turned in. I had to maneuver into a parking spot, and the doors locked back when I put it in reverse. I came back out of the store and everything went crazy. It wouldn't start, it said the shifter was in 2nd or 3rd gear when it was clearly in park, and the gauges were not all working. I cycled the ignition a few times and it finally started and seemed "normal". I turned out onto the road and immediately got the CEL solid with the reduced engine power warning on the DIC. I pulled over at a gas station and didn't try moving it again.

I called my mechanic and explained everything that had happened and he didn't even want me to bring it to him. A mechanic he referred me to thought that it was a throttle body issue, in either the throttle body and it's wiring or the gas peddle assembly. I tried a couple of times to cycle the ignition again and it quit trying to start. I cleaned the battery connections and tried to jump start it and it still didn't try to start. All the light were on and bright. I did notice that the DRL's were staying on and stayed on the entire time it was towed home.

At home it continues to do nothing when you turn the key. The key fob won't unlock the doors unless the key is in it and on. The lights are still bright and the battery checks at 12 volts. I did notice that the throttle body makes more noise the first time you turn the key after reconnecting the battery, but I may not have noticed that in the past. I left the battery disconnected. The gauges still don't move when you turn the key.

What in the world is going on with my truck? Where do I start without replacing a bunch of parts and hope to get lucky? I'd appreciate anything you would recommend at this point. Thanks in advance!

Edited July 14, 2020 by stephenclark4

diyer2 · July 14, 2020

12 volts is low. Should be above 12 volts. How old is the battery.

Check grounds. There are a few grounds located around the truck.

Simple place to start.

Formulabruce · July 14, 2020

As mentioned above BCM ground is first. Under the drivers door, on the cab mount, facing to the rear.

Next ,Back of pass side of block to firewall ground.

Next is try a battery that has 12.6 + volts in it.

stephenclark4 · July 14, 2020

Just tried to start the truck before I saw the replies above. I haven't made any changes to it, just wanted to see if it would do anything today. Connected the battery and the truck started fine, with just an initial sputter, then idled fine. I wiggled the TB connector and the MAF connector to see if it would error. No issues. After letting it idle for about 5 minutes, I thought I'd try to drive it around the block. The engine died before I could get to the street. Here's a look at the instrument panel when it died. Security light coming on due to a possible ground issue and killing the engine?