2003 Chevrolet Tahoe/190,000 miles/ 4.8Liter V8 engine

I’m having problems with my Tahoe going into limp mode, code P1518. I appreciate any insight and have posted the history below:

History of the problem:

1st problem with P1518: March 2020, 174,000 miles, Code P1518

-Vehicle would go into reduced power mode. On the dash, the transmission light, ABS light, and brake light would come on

-The doors would lock and unlock, and the interior lights would flicker on and off. Power steering would not work.

1st repair, March 2020, 174,000 miles:

- Rear wheel speed sensor was replaced

- TAC module was replaced

2nd problem with P1518: March 2020, 174,025 miles, Code P1518

The day after I got the vehicle back from the service department, it went into reduced power mode again, code P1518

2nd repair, March 2020, 174,100 miles:

-G104 was relocated to the back of the cylinder head and all grounds were cleaned

-traced the wiring and found a loose connection causing poor connectivity putting strain and causing heat build up; this issue was corrected

3rd problem, Sept. 2022, 183,000 miles, Code P1518

-Vehicle had been sitting in the garage for a few days. It went into reduced power mode when it had been driven for approximately one block.

-On the dash, the transmission light came on. I cleared the code and it drove fine the rest of the way.

Current and Continuing problems with code P1518 & reduced engine power-Sept. 2022-the present ( November 2024, 190,000 miles)

-When this happens, it is always after the Tahoe has been sitting in the garage for a few days. It goes into reduced power mode within the first 10-15 minutes of driving it.

-On the dash, the transmission light comes on. I clear the code and it drives fine the rest of the way.

I appreciate any insight anyone could offer.

 

One more thing I forgot to add: Turning on the air conditioner causes a noticeable strain on the engine, so I am avoiding running it. Maybe this is related in some way?

 

Every single time I have had that message pop up (along with the slow as hell acceleration, lol), it has been when starting the vehicle after its been sitting for a couple/ few days. The battery will usually measure a couple volts low, and/ or the terminal connections at the battery will be slightly loose or corroded. My quick fix (laziness or can't afford to replace the cables or battery just yet) is to pull over, shut off the suburban, pop the hood, and give the battery cables a little twist in the tightening direction, or if I have a little adjustable wrench, I'll tighten them a little bit on the battery. I'll turn the key on, wait for the fuel pump to pressurize ( a couple seconds), and then it'll start just fine, full engine power restored... until next time :-)

Edit: P1518 pops up also, half the time, and illuminates the check engine light. But it'll go away on its own after driving it a couple times

 

Very interesting--thank you for shaping this insight!
Do you know the voltage range for a healthy battery? (I searched online and got a wide range of numbers.) My battery showed 12.2 volts, cold, when I checked it a few days ago.

 

That is an acceptable voltage. There will be a drop when cranking the engine, as well as another drop even when just turning the key to the on position. I don't know the exact voltage cut off, but it's likely about 10 or 10.5 volts before it will give the reduced engine power code.