2003 Yukon Reduced Engine Power

[Tatman71]

I have been having issues with my 03 Yukon. Runs like crap, no power and goes into Reduced Engine Power mode frequently. I have changed plugs, wires and all coils a week ago dure to random misfires. I previously replaced the throttle body with a new tps on it and the accelerator pedal module. No change. I borrowed a scan tool and am getting numerous codes. Ones telling me basically replace tps or the app.
I am lost on how to fix it.

 

[Fless]

Welcome to the forum!

Carefully inspect the wiring harness from the throttle body connector back six inches or so; others have had wires that are broken or compromised underneath the insulation. Should be able to flex the wires in your fingers to feel for any bad spots. Also check pin fitment at the throttle body connector.

 

[Sam Harris]

Welcome from Texas! Too bad you did all that work (and spent all that $$), and still don’t have a fix. Hoping the sage advice from @Fless takes care of your issue. Either way, you’re in the right place for whatever help you need.

 

[rockola1971]

Yup. It should be mandatory to replace the wiring pigtail with plug when the TPS is replaced. Its a very well known problem that the wiring harness that plugs into the TPS doesnt hold up well to the natural engine vibration and heat. The wiring in this harness is stranded copper wire and will eventually break under the load of vibration over years of use. Dont confuse the break with an obvious break in the insulation AND the wire itself. Seldomy does the wire actually completely separate itself from the plug or as far back as 6-12" away from the plug. BUT you can usually feel the break if you run your fingers over each wire while grasping with your fingertips of your thumb and index finger. The plug with pigtail is actually a part than you can buy at just about any auto parts store and even rockauto. Thats how common of a problem it is. Then there is the possibility of the TAC(Throttle Actuator Control) module wiring plug partially dislodged from its female socket counterpart OR corrrosion at the plug at the TAC module. The TAC module is between the vac brake booster and fender on the firewall. Its a little black flat box.

 

[MassHoe04]

Timing (pun intended) on this question/issue couldn't be better...

Check out @tomloans write-up. Maybe there is something in there to help your situation.

Reduced Engine Power write-up

Hello all. Thought this might help someone who has had this issue over and over again. The best write up I have seen... Hello all, For anyone reading this old post regarding the numerous years of Silverado's going into "reduced power mode" I will share my findings, hope this helps someone...

www.tahoeyukonforum.com

 

[mwilson62000]

Also check the connectors at the TAC module(drivers side, mounted on the firewall.) On my 03 while running, I could wiggle the 16 pin connector and make it go into limp mode. Ordered a new connector(from LMCtruck.com I think) and spliced and soldered wires to new connector. Didn’t have REP while driving again.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[Tatman71]

Timing (pun intended) on this question/issue couldn't be better...

Check out @tomloans write-up. Maybe there is something in there to help your situation.

Reduced Engine Power write-up

Hello all. Thought this might help someone who has had this issue over and over again. The best write up I have seen... Hello all, For anyone reading this old post regarding the numerous years of Silverado's going into "reduced power mode" I will share my findings, hope this helps someone...

www.tahoeyukonforum.com

I did see that. We had already replaced all the grounds prior to seeing that. That helped rule that out. Thank you for sending me the info. Everyone that has replied has been a big help.

 

[MassHoe04]

I did see that. We had already replaced all the grounds prior to seeing that. That helped rule that out. Thank you for sending me the info. Everyone that has replied has been a big help.

OK. We have some really great diagnostic minds here to check all the possible causes and walk you through steps to identify and fix your issue.

 

[S33k3r]

On our 2005 Suburban 2500, we had water intrusion at/near the ECM. The ECM itself was okay, but the wires leading to it had corroded, cracked, and some were broken.

 

[S33k3r]

On our 2005 Suburban 2500, we had water intrusion at/near the ECM. The ECM itself was okay, but the wires leading to it had corroded, cracked, and some were broken.

My wife drove through water up to her wheel wells; It took us 6 weeks and 2 mechanics to get it sorted out. But a friend recommended a local mechanic; he figured it out, fixed it, explained it to me, and didn't charge me the arm and a leg it SHOULD have cost to track down this electrical demon.

My wife and daughter just got back from a round trip to Mississippi in it.

 

[Tatman71]

Ok. Replaced the throttle body wiring harness. Also replaced the T.A.C. module.. Seen the date on my battery of 8/16. So just to make sure I replaced the battery. Still will not come out of reduced power mode.
To recap. Plugs and wires were changed. Still random miss fire. All coils were replaced. Random miss fire fixed. Still going in reduced power mode. Codes pointed towards tps and/or foot pedal sensor. Replaced throttle body, tps and foot pedal sensor. Still reduced power mode. Upon advice I checked and replaced tps wiring harness. Still in reduced power mode. Also upon advice replaced the T.A.C. MODULE and battery today. Still in reduced power mode.
Attached is a picture of the codes still being thrown. Not sure whats next.

 

[tomloans]

Super important that when you replaced the wiring harness, you solder the connections - this is a must. Again this is a must. Do not use crimp connectors or solder connectors of any kind. This is must do.
The two grounds behind your engine can be the issues as well. There is a thin ground wire that will often break on the passenger side of the back of the engine. Be sure that is corrosion free and not broken off. There is a ground strap bolted to the fire wall and the back of the engine on the driver side. The firewall connection is usually corroded - you can't tell by looking at it. Take it off and brush it and the firewall contact point as well. You will see white dust coming off of it. Reattach after cleaning. Under the passenger side under the carriage you will find 3 grounds attached to the frame. Remove the screw/bolt and brush thoroughly each wire connection and both sides of the frame until you see shiny metal. GM coated the metal then attached the grounds ( great move!). Finally and again I repeat, the wiring harness needs to be soldered and then use shrink tubing to cover them. I can't be more emphatic about this. Also be very careful as you can easily make another break when manipulating the old wiring. Remember the heat and vibration caused the break. This means is can easily break somewhere else along the lines as you are messing with them. Be careful.
Also you mentioned that the reduced engine power hasn't gone away. Has the symptoms changed at all while replacing parts or has it been exactly the same? Some time like in my case, one part would solve the problem for a few years and then I would have another issue but the way reduced engine power would rear its' ugly head was different. For instance this last episode was only during idling or first start up.

You are not alone. Don't give up... Read the comments as well

 

[OR VietVet]

Yea, that TPS harness is recommended in the different TPS choices at RA. Well known problem and RA gives the harness part # with the TPS part #.

Suggestion, the PCM is mounted next to your battery and is really kind of hanging out there. I recently sent mine in for a tune at BBP and I saw how exposed it is. I was very careful to clean and inspect before I re-installed it. The TPS harness should be soldered as @tomloans said, but for now, I would assume you would not have the exact same problem if you butt connected them when you did yours.

For S*H*I*T*S and giggles, do you have good exhaust flow, so you can rule out a clogged exhaust? Low % of that being the problem but if I experience any loss of power I always do 3 things: check exhaust flow, check fuel pressure and check for a binding brake. With the codes you got, I doubt either is the problem but I am a*n*a*l about crap like that.

Welcome to the forum.

 

[S33k3r]

...but I am a*n*a*l about crap like that.

Isn't that kind of why you are a good mechanic? you left no stone unturned when you were trouble-shooting?

It has been my experience that when something is skipped because "that can't be the problem" that you find out that was the problem.

 

[OR VietVet]

Isn't that kind of why you are a good mechanic? you left no stone unturned when you were trouble-shooting?

It has been my experience that when something is skipped because "that can't be the problem" that you find out that was the problem.

Sometimes there is no excuse for "tunnel vision" when you are supposed to be an open minded tech. To this day, I still work on the side. I ask so many questions about a problem, that I have independent people say, "I have never been asked so many questions". I am in the running for a service manager job here locally. I love running shops.

 

[S33k3r]

Sometimes there is no excuse for "tunnel vision" when you are supposed to be an open minded tech. To this day, I still work on the side. I ask so many questions about a problem, that I have independent people say, "I have never been asked so many questions". I am in the running for a service manager job here locally. I love running shops.

If we vote for you, can we get any discounts?