Here is a ? for u guys maybe u all can help me out. I have a 04 sierra with the 5.3. It has a tune,cold air intake, tb bypass,and headers as mods...well here is what is going on. When i start the truck sometimes it says REDUCED ENGINE POWER. After I turn it off and on a couple of times it works fine. It also does this when I floor it. what could it be? They told me that one of the battery wires was loose and that was causing it to do that but I tighten both of em and it is still doing that.

 

Possible Problem With Tune...

It Goes Into The Reduced Power Mode To Protect It....

 

my bullydog programmer does it every time i take it off and put it back on and when it does it throws a engine code like c107 or sumthin, but i can clear the dtc codes on my programmer by bullydog so i just do that and its fine after that. but idk it prolly is your tune tho.

 

You'll have to read the DTC that is set to help pinpoint the cause. Could be a mechanical/electrical issue or the tune.

 

My dads '03 did that..it ended up being the throttle position sensor in the DBW pedal, replaced the whole unit and it was good to go

 

I agree. I feel it has something to do with your TB or pedel.

 

Throttle Actuator Control System(this includes the pedal position sensors, TAC Module, TB, wiring and TAC to PCM communications) faults are the prime suspect, particularly if REP is triggered before the engine even starts. i.e. just turn the key to the RUN position and see if it goes into REP mode. Turning the key to the OFF position for at least 15 seconds will reset/clear REP if the fault is no longer present.

There is a TSB for an internal break in the yellow wire within the first 4 inches from the throttle body: "SES light and reduced engine power with a DTC P1516. DTCS P0120, P0220, P1514, P1515, P1518 and P2135 may also be present."


Other faults in the system will set other DTCs. e.g. P2135 if there is a disagreement between the TPS1 and TPS2 signals.

 

well guys had my truck check for the tune and it is not that but it is still doing this once in a while. when i turn it to RUN it does not give out the REP code only when i turn it on???

 

What kind of tune do you have? Mail order? handheld? Also, usually reduced engine power will flash when you are flashing the pcm, i would think it's a sensor. You need to scan that truck and see what codes pop up, that will tell you. And when you say you had your truck checked for the tune, who checked it and how do you know it's not the tune?

 

Reduced engine power is a function of the electronic throttle control system. It can come up when the calculated/measured airflow is outside of the pre-defined maximum limits, or it can come up when a signal is lost somewhere in the chain. Given your mods, it will not be the first option, so you have some sort of signal problem, somewhere in the Pedal->TAC->PCM->TB chain...