Reduced Engine power, Check Engine.. and other errors...

[Maximus1]

Mine did this about a month ago, I just pulled into a parking lot turned it for about a minute then it started up just fine and ran fine, no problems since. Had my codes read about two days ago and got my left front wheel speed sensor wasnt reading and something about fuel evaporator or something like that, think it had something to do with the gas cap. But I dont think either of those codes had anything to do with the "Reduced Engine Power"

Actually I believe that the wheel speed sensor can put the truck into "reduced engine power mode" I'm having the same issues. Here's what I've done so far.
1. Cleaned the grounds on the backside of the engine and the main ground on the driver side of engine
2. Replaced the TPS sensor twice
3. Replaced the TAC module
4. Replaced the pedal sensor
5. Replaced the TPS pigtail
6. Checked the wiring from the TPS to the fuse box and then from the fuse box to the module and from the module to inside the can to the pedal

So today the "Reduced engine power" came on after doing all of these repairs, but it only came on after going over a really bumpy road and the ABS light came on. I'm going to replace the driver side wheel speed sensor and see if that corrects the problem. I'll give some feedback when I replace it

 

[Maximus1]

So I was on my way to get an wheel speed sensor and the truck just quit while I was driving. No warning of a reduced engine power code or anything.

Now it won't even crank.
I replaced the starter, didn't help, replaced the ignition switch and that didn't help either. When I turn the key to the on position I noticed that the indicator that tells you what gear your transmission is in doesn't illuminate. I jumped the starter relay and the truck will crank over but won't start. Anyone have any ideas? Maybe ECM?

 

[Maximus1]

Neutral safety switch?

 

[PG01]

I didnt read all the posts but did you check your battery leads, starter wires, GROUNDS, especially grounds, batt to frame, engine to firewall....etc,etc... seriously man....

 

[Maximus1]

Yes I cleaned all the grounds including the two behind the engine block and I even added a ground.

I replaced the ignition housing that contains the anti-theft sensor. That did absolutely nothing. I still have the same problem.

Today I have come to the conclusion that my ECM is bad. I have used two different scan tools to try and get a P-code but both scanners could not communicate with the ECM.

 

[Maximus1]

I'm having it towed to my friends shop, he has the ability to flash a new ECM and install the HP tuners program that I have for the aftermarket performance cam that I installed on the 5.3L engine.

 

[Maximus1]

UPDATE:
So I had it towed to my friends shop and he said that he removed the ECM and hooked it up to a harness that he setup for tuning and said that the ECM was fine and was communicating with his tuner. So he plugged it back into the Tahoe and it wouldn't communicate. He wasn't sure but he said that I had a short somewhere and that he really didn't have time to look for it because he was already two weeks behind on customer vehicles which is understandable so I am having it towed back to my house. At least I know that it's not the ECM.

So now what? I'm pulling out my hair trying to figure it out. Also this is my daily driver so I can't wait 2 weeks for it to be repaired.
New parts so far
Starter
Ignition switch
Ignition switch housing with pass lock
Neutral safety switch

Anyone know where I should start next? I was thinking of removing the fuse block under the hood and checking the wiring from there first. Any help or ideas would be greatly appreciated.

 

[PG01]

Yes, pull the fuse block under hood apart amf clean it up.... betcha its corroded under there.

 

[408sjtahoe]

So reading all these different topics in regards to "service stabletrak, service traction control, engine power reduced" my wifes tahoe this passed weekend just got worse. It had happen maybe 3 times before within this passed year but all times we were able to start it after 5 min and never came up until this passed Friday, It did it Thursday but again it started right up. i had a brand new radio installed friday but i'm hoping that wouldn't of effected it in any way? So once it was installed i tried to get it going and thats when the error kept coming up. The good thing that is was in my folks driveway, but that error wouldn't go away so unfortunately we had it towed to a mechanic shop. Still waiting to here from them but with so many areas that could cause this, has any one ever found out what actually causes it?

The worst one that i read was having to fork out $1400 to get lifters fixed

its a 2008 Chevy Tahoe 5.3L, her daily.

 

[M1Gunner]

Ok so just hear me out on this... start your truck, turn on the ac so that the ac switch light is illuminated. Gently wiggle the key while it's in the ignition. Watch for anything unusual like the ac button light to go off or flicker. Watch the gauges to for anything unusual. Any bulb tests or gauge reset/recal.
Idk how many keys you have on your key ring or if it's weighted down at all but the ignition switch is sneaky bastard in these situations.

Not saying that's your problem but it is a possibility.

Any history codes for lost comms?

 

[408sjtahoe]

got the call yesterday from the mechanic and it ended up being the gas pedal sensor, so the whole pedal must be replaced. $297 total, its not bad but i do hope this is the fix as I've heard others fix this and other parts related to this issue and still get that error message.

 

[Maximus1]

got the call yesterday from the mechanic and it ended up being the gas pedal sensor, so the whole pedal must be replaced. $297 total, its not bad but i do hope this is the fix as I've heard others fix this and other parts related to this issue and still get that error message.

I really hope that fixes your problem, but I'm a mechanic for 20 years and thought the same thing when I kept getting the reduced engine power code. The pedal sensor fixed my problem for a little while then came right back.

I took it to the dealership and come to find out my cranking issue was because one of the ground wires on the back of the engine didn't get connected back when I cleaned them and that's why it wouldn't start.

After speaking with the mechanic at the dealership he said that everytime one of these Tahoe's (2000-2007) comes in with the reduced engine power code is always linked to a bad ground issue. He told me that even if you remove and clean them that they still may not get a good ground. GM knows about this problem but refuse to issue a recall. What he did with mine and all the others that come in is this.

On the main harness running from the fuse box to the engine, find the black wire with a white stripe. Cut this wire and splice it adding a extra wire on one end and then run it directly to the negative side of the battery. This is what he did to mine and all I can say is WOW! That has not only fixed my reduced engine power problem but now the throttle is a lot more responsive and quicker to react. I wouldn't normally condone cutting any wires on a main harness to an engine but this really helped out. It not only boosts the ground to the back of the engine but also to the fuse box and TAC module. I hope that this information will help anyone who finds themselves in the same situation as I was. After replacing nearly every piece related to my throttle body including the harness from the pedal to the TAC module it all came down to a known grounding issue that cost me literally a couple bucks for some wire and a splice kit. My headache that I've had for the last 7 days is gone. Good luck

 

[Zeke]

I'm in the same boat. 2004 Tahoe 5.3 Flex fuel. Replaced grounds, replace TAC module, cleaned throttle body, replaced both the TPS sensor and pedal sensors twice. I STILL HAVE the reduced engine power. Codes U0107 P1526 and a third that I can't remember also today my ABS light came on. I'm going to replace the whole throttle body next and if that doesn't work then I'm replacing the ECM unless someone else has a better idea.

I

 

[Maximus1]

One other note is to have your alternator tested not just to see if it's charging but also have the voltage regulator tested that is built into the alternator. Mine passed the charging test but failed the regulator test. I was having wild voltage swings from 12.0 all the way to 18.6. This caused all kinds of electrical problems including blowing fuses which made me think something else was wrong. This is my third alternator in less than a year. Luckily I bought the lifetime warranty alternator so it's replaced for free. These aftermarket alternators are junk. I believe if this one goes out I'm going to return this one and get my money back and then go to the GM dealership and buy the OEM alternator. The original alternator (AC Delco) lasted over 11 years. These duralast ones are made in China and they can't seem to make one with a good regulator.

 

[uscjfs2012]

I really hope that fixes your problem, but I'm a mechanic for 20 years and thought the same thing when I kept getting the reduced engine power code. The pedal sensor fixed my problem for a little while then came right back.

I took it to the dealership and come to find out my cranking issue was because one of the ground wires on the back of the engine didn't get connected back when I cleaned them and that's why it wouldn't start.

After speaking with the mechanic at the dealership he said that everytime one of these Tahoe's (2000-2007) comes in with the reduced engine power code is always linked to a bad ground issue. He told me that even if you remove and clean them that they still may not get a good ground. GM knows about this problem but refuse to issue a recall. What he did with mine and all the others that come in is this.

On the main harness running from the fuse box to the engine, find the black wire with a white stripe. Cut this wire and splice it adding a extra wire on one end and then run it directly to the negative side of the battery. This is what he did to mine and all I can say is WOW! That has not only fixed my reduced engine power problem but now the throttle is a lot more responsive and quicker to react. I wouldn't normally condone cutting any wires on a main harness to an engine but this really helped out. It not only boosts the ground to the back of the engine but also to the fuse box and TAC module. I hope that this information will help anyone who finds themselves in the same situation as I was. After replacing nearly every piece related to my throttle body including the harness from the pedal to the TAC module it all came down to a known grounding issue that cost me literally a couple bucks for some wire and a splice kit. My headache that I've had for the last 7 days is gone. Good luck

I really hope that fixes your problem, but I'm a mechanic for 20 years and thought the same thing when I kept getting the reduced engine power code. The pedal sensor fixed my problem for a little while then came right back.

I took it to the dealership and come to find out my cranking issue was because one of the ground wires on the back of the engine didn't get connected back when I cleaned them and that's why it wouldn't start.

After speaking with the mechanic at the dealership he said that everytime one of these Tahoe's (2000-2007) comes in with the reduced engine power code is always linked to a bad ground issue. He told me that even if you remove and clean them that they still may not get a good ground. GM knows about this problem but refuse to issue a recall. What he did with mine and all the others that come in is this.

On the main harness running from the fuse box to the engine, find the black wire with a white stripe. Cut this wire and splice it adding a extra wire on one end and then run it directly to the negative side of the battery. This is what he did to mine and all I can say is WOW! That has not only fixed my reduced engine power problem but now the throttle is a lot more responsive and quicker to react. I wouldn't normally condone cutting any wires on a main harness to an engine but this really helped out. It not only boosts the ground to the back of the engine but also to the fuse box and TAC module. I hope that this information will help anyone who finds themselves in the same situation as I was. After replacing nearly every piece related to my throttle body including the harness from the pedal to the TAC module it all came down to a known grounding issue that cost me literally a couple bucks for some wire and a splice kit. My headache that I've had for the last 7 days is gone. Good luck

Can you tell me or show me which black wire with white atripe you are talking about? My 2003 tahoe has several small black wires with white strips running from fuse box to engine.

 

[reath1]

For anyone else that runs into this issue, I highly recommend following Maximus1's advice. I, too, know my way around under a vehicle. I fought the P1516 and P1518 for 3 days. First, removing the ground from the right rear of the block extending it to a firewall stud. Checked ground continuity. 1.6 ohms. I thought that that was a good ground. It would easily light a test light. Still had the codes. I then changed the TBS, TBS harness, TAC module, APS and finally the TB. All to no avail. At that point I used Maximus1 advice above. Opened the harness right off of the underhood fuse block. About 12 inches from the fuse block you'll find a factory splice of 3 blacks w/ white stripes going into one. Jump off right there with a new ground going straight to block. I went to one of the lower bolts on the alternator bracket. One holds two grounds already. I went to the other one. Ohm'd that new ground at 0.00. Cleared the codes and cranked it up. No codes.

 

[00chevyHd]

mine has voltage problems i looked at some videos and found out if i move this ground point to the firewall would it be okay if i take the risk heres a pic of the bolt on back of the engine block help please

 

[IrishScout76]

What ended up working for you? I’m in the same boat now. I’ve replaced the TAC, MAF, cleaned the throttle body, APP, and added cold air intake. Still in limp mode and throws a p1125. I’ve checked the harness…wires and pins look fine. I’m about to set the damn thing on fire in my driveway!!

 

[tomloans]

For anyone else that runs into this issue, I highly recommend following Maximus1's advice. I, too, know my way around under a vehicle. I fought the P1516 and P1518 for 3 days. First, removing the ground from the right rear of the block extending it to a firewall stud. Checked ground continuity. 1.6 ohms. I thought that that was a good ground. It would easily light a test light. Still had the codes. I then changed the TBS, TBS harness, TAC module, APS and finally the TB. All to no avail. At that point I used Maximus1 advice above. Opened the harness right off of the underhood fuse block. About 12 inches from the fuse block you'll find a factory splice of 3 blacks w/ white stripes going into one. Jump off right there with a new ground going straight to block. I went to one of the lower bolts on the alternator bracket. One holds two grounds already. I went to the other one. Ohm'd that new ground at 0.00. Cleared the codes and cranked it up. No codes.

This is an old thread but curious if anyone can point out which wire was grounded. See below what I found and please confirm for me. Thank you!