2003 HD1500 "reduced power mode" back to the drawing board

ifixedit · January 25, 2016

I thank you for the information, my truck just told me the reduce engine power code. I was looking at many parts of the normal, have to look more into the wires and ground. Thanks again.

A little update for anyone reading this. Turned out the culprit in the end after I chased every other possibility was the damn wiring harness that goes from the accelerator pedal through the firewall to the TAC module. If you think this could be the issue or to see if it possibly is, start your truck, let it idle and wiggle the wires going from the accelerator pedal to the firewall, you may suddenly notice a change in idle speed or it will prompt the truck to go into reduced power mode. It can be tough to duplicate this repeatedly as I could not get it to do it every time, but of course would do it at the most inconvenient times like when I was on the freeway, then you gotta pull over, shut the truck off and hope it re-sets, all the while damn near getting ran into (not good). Another test is to turn the key to run (don't start the engine) and push the accelerator pedal all the way to the floor and release it, this in my case 8 out of 10 times would also cause it to display 'reduced power mode.'

My solution was to go to a junkyard, I plucked a complete accelerator pedal and harness assembly from a clapped out '03 for $35. DO NOT UNPLUG OR TAKE THE ASSEMBLY APART AS THIS COULD CAUSE CONNECTIVITY ISSUES, JUST LEAVE IT ALONE! Take your old pedal assembly and harness out and replace it entirely as complete unit with the new one. GM must have made a mid- year change as I noticed the one I got had heavier gauge wires compared to the one I took out. My truck did have to 're-learn' the range of the new pedal (no big deal), but I've been driving the truck about 6 months now and no reduced power mode at all. Good luck!

GirlTruck · June 18, 2017

looking for feedback and wondering if it is a wire harness issue as described in prior post ...

check engine light came on months ago. i took it in the Autozone they put their machine on it and said they could not find anything, could be the gas cap. I did disconnect my battery terminals to reset and that didn't work so I let it go since nothing seemed wrong. then my headlights stopped working a couple months later. My work-around for this is manual high beams. today i drove it for less than 5 min and the reduced engine power message. i do smell gas but i thought it was because i have a gas can that i filled yesterday in the bed. ?? advise..?

ifixedit · June 29, 2017

First thing is pull the codes to see what it is telling you. You're likely to have 2 - 3 different codes. I don't have the code numbers in front of me at the moment but the likely codes to come up will pertain to issues with the TAC (throttle actuator control, DON'T WASTE YOUR TIME REPLACING IT!) or a correlation issue between the pedal sensor (the one on the gas pedal) and the TB (throttle body).

If it is any of these codes it is likely just a simple grounding issue, the challenge is figuring out where the grounding issue is

However, for more ideas and things to look at read through this entire post I did elsewhere here on the subject >>> http://www.gm-trucks.com/forums/topic/161040-dreaded-reduced-engine-power-issue/

Bigfutz · July 21, 2017

2003 Yukon. Replaced the throttle body pigtail, soldering the connections and sleeving each wire with waterproof shrink tubing. Nailed it, many miles ago.