Solution to Reduced Engine Power Message and p1516. Look Here

[mdmcinti]

I am sure this topic has beat to death on every GM truck and SUV forum out there in the internet, but I would like to share what I have found to fix the dreaded Reduced Engine Power message. I am sure more and more owners of these vehicles are experience this issue as these vehicles age. I also want to help people save money and not throw unnecessary parts into trying to solve this issue. Also this will help the people that replaced everything and are still getting the issue and can’t seem to figure it out.

Well to start, this problem is a grounding issue. There are two troublesome grounds on the backside of the motor that are the main culprit. In my case these grounds weren’t frayed or broken, so I made some new grounds to fix the issue. I made them from 10 gauge stranded copper wire and crimp ring connectors that I had sitting around. The first ground goes to from the fire wall to the engine block. I used one of the not used threads in the driver side valve cover. I happen to have a 10 mm bolt that fit this thread so I lucked out. You can probably use the bolts on the alternator bracket. The second ground I made goes from the TAC module to the fire wall. I decided to ground this just in case there is a grounding issue related to the TAC Nadine because the code p1516 is where communication is lost from this module. Here are the pictures of my grounds. I plan on getting some wire loom to make them look more factory.

I also found this solution from a YouTube video where this guy did everything and then made these grounds to solve his problem.

Also, checking the other grounds on the truck and cleaning them will help in with this and other future issues.


Ground locations

1. On the frame on below driver side door/b pillar

2. Front of frame on driver side. Small battery cable goes to this as well as another ground.

4. Passenger side of engine block. The big negative battery cable goes here.

5. Backside of motor on the passenger side. It is next to the cam position sensor. Comes off the main harness.

6. Back side of driver side cylinder head. Very difficult to reach

7. The aluminum ground strap that goes from backside of driver side cylinder head to the fire wall on driver side. It attaches to the same point as ground I mentioned in point 6

8. Ground strap that goes from hood to fire wall

9. This ground is on the interior. It is on the driver side a pillar. You will have to remove the a pillar trim to access it

One last thing I forgot to mention, is to check the pig tail that goes to the plug that connects to the throttle body. The wires on this can break, or come apart inside the plug. I would recommend checking into this first and then grounding the motor is fixing this wire pigtail does not work. They make a replacement pig tail that is cheap and it worth while doing. I don’t this the TPS, the TAC module, or the gas pedal sensor rarely ever go bad on these vehicles. When I got my rig, the previous owner replaced the pigtail for the throttle body and the TPS. I was having this issue and I am sure they could not figure it out so they traded it in. I did this fix on Saturday, and I have cold started my truck at 5 am all week and I have not had a reduced engine power message at all this week. Last week I got it on three mornings and one time in the afternoon when I hit a bump. I will do a long term update after a month.

I think covered it all. If I missed anything or if there are any other suggestions to fix this issue please let me know.

 

[Joseph Garcia]

Thank you for your detailed report on what you did to eliminate that code. Ground issues are common on these trucks, and your specific remedy increases our collective knowledge base on this specific issue and a working resolution.

Thanks again.

 

[mdmcinti]

Thank you for your detailed report on what you did to eliminate that code. Ground issues are common on these trucks, and your specific remedy increases our collective knowledge base on this specific issue and a working resolution.

Thanks again.

No problem. This reduced engine power really was bugging me and I was hoping to fix this before it got cold up here in Nevada and it would have given me trouble all winter. I figured since I mastered this electrical issues, I would share with the world and anybody else that googles this problem and stumbles upon this thread. I am glad to have it fixed though.

 

[OR VietVet]

No problem. This reduced engine power really was bugging me and I was hoping to fix this before it got cold up here in Nevada and it would have given me trouble all winter. I figured since I mastered this electrical issues, I would share with the world and anybody else that googles this problem and stumbles upon this thread. I am glad to have it fixed though.

This link also helps explain these issues: https://www.fixmyoldride.com/Chevro...e7e5cd24ed24635&at_ab=per-2&at_pos=3&at_tot=4

 

[mdmcinti]

This link also helps explain these issues: https://www.fixmyoldride.com/Chevro...e7e5cd24ed24635&at_ab=per-2&at_pos=3&at_tot=4

I remember reading this last weekend. I kind of forgot about it. Basically if you want the electronics to function properly in these trucks, you better maintain all grounds, do the big 3 at least, and add extra grounds in my case

 

[OR VietVet]

Based off of your post I am assuming this all relates to the 2003 and on, drive by wire rigs. I likely will not see this problem on my 2002 with an actual throttle cable, correct?

 

[mdmcinti]

Based off of your post I am assuming this all relates to the 2003 and on, drive by wire rigs. I likely will not see this problem on my 2002 with an actual throttle cable, correct?

Yes sir that is correct. I do not know if this will work for 2007 and later models having this issues, but it for sure will fix the problem do trucks and suvs from 2003-2007 classic.

 

[mdmcinti]

Sorry to bring this thread up back from the dead, but this ground solution I shared was not the cause of my reduced engine power problem. It worked for a while, but it eventually came back, especially as it got colder at night during the fall. It’s getting bad now since it has gotten as low as 9 degrees some nights and has snowed and rained a few times. It actually turned out that whoever installed the after market pigtail when they replaced the tps sensor did not do a good job crimping the wires together. This was giving a loose connection of the wires allowing this condition to occur on cold starts and when I hit a hard bump in the road. How I figured this out was I was watching a scanner danner video on YouTube trying to diagnose this problem on a 2003 express van. The van owner had the same parts changed out when the problem occurred and it fixed the problem for a few years then it started coming back. Well when they were going though everything, they found one of the crimp connections being bad and easily pulled a wire out from the connector. They figured that was the root cause of the problem so I thought to give it a second look. Well I turned my rig on and grabbed the wire harness pigtail and gave it a shake. The idle immediately changed to what it does on reduced engine power mode and I looked at the cluster and sure enough it was in reduced engine power mode. Well I went through it today and I found two connections that were kind of loose so I took the crimp connectors off and recrimped the wires together. I went ahead and started the truck, took the harness and wiggled/shook it around and the problem did not come back. So I have think I have officially solved this problem. I will update Thursday after 2 cold starts before I go to work because it’s been doing it pretty often on cold starts after the vehicle has sat overnight.

 

[bigdog9191999]

Sorry to bring this thread up back from the dead, but this ground solution I shared was not the cause of my reduced engine power problem. It worked for a while, but it eventually came back, especially as it got colder at night during the fall. It’s getting bad now since it has gotten as low as 9 degrees some nights and has snowed and rained a few times. It actually turned out that whoever installed the after market pigtail when they replaced the tps sensor did not do a good job crimping the wires together. This was giving a loose connection of the wires allowing this condition to occur on cold starts and when I hit a hard bump in the road. How I figured this out was I was watching a scanner danner video on YouTube trying to diagnose this problem on a 2003 express van. The van owner had the same parts changed out when the problem occurred and it fixed the problem for a few years then it started coming back. Well when they were going though everything, they found one of the crimp connections being bad and easily pulled a wire out from the connector. They figured that was the root cause of the problem so I thought to give it a second look. Well I turned my rig on and grabbed the wire harness pigtail and gave it a shake. The idle immediately changed to what it does on reduced engine power mode and I looked at the cluster and sure enough it was in reduced engine power mode. Well I went through it today and I found two connections that were kind of loose so I took the crimp connectors off and recrimped the wires together. I went ahead and started the truck, took the harness and wiggled/shook it around and the problem did not come back. So I have think I have officially solved this problem. I will update Thursday after 2 cold starts before I go to work because it’s been doing it pretty often on cold starts after the vehicle has sat overnight.

so how has this been holding up for you? I am going to be diving into reduced power issues with our 03 denali soon. figured I would start with this type of thing before I start dumping things like throttle bodies and such at it. mostly because I am cheap!

 

[mdmcinti]

It’s holding up great. I put 10k plus miles on my Yukon after I found the root cause of my reduced engine power. It has not come back and it’s been almost four months. The truck is sitting now since it decided to have a lifter spin/collapse back at the end of December and take the cam with it. It runs fine and doesn’t miss, but it has horrible lifter knock and so it is parked until I get some money together to fix it this spring.

Yes, I think the throttle body does not ever fail and I have a Forman sensor on mine. I would check the wiring from the pigtail to the plug because those tend to come loose. The. I would check all the ground. The two big ones are on the back of the motor and they are pita to get to unless you have the intake manifold off. Also doing my grounding trick would help to. I kept all my grounds on for the heck of it since they were not hurting anything. Also the TAC module never fails either. It’s all in the wiring. I was also reading that it seems like 2003 is the year that seems to have this issue and some guy on another forum found that the wiring harness for the pedal and the tac module have a smaller gauge wire compared to a harness and pedal he took out of a 2004 plus truck. So GM fixed it with thicker wires on the later trucks.

I hope you figure out the problem I kept getting p1516 with this problem. Good luck!

 

[Tonyrodz]

It’s holding up great. I put 10k plus miles on my Yukon after I found the root cause of my reduced engine power. It has not come back and it’s been almost four months. The truck is sitting now since it decided to have a lifter spin/collapse back at the end of December and take the cam with it. It runs fine and doesn’t miss, but it has horrible lifter knock and so it is parked until I get some money together to fix it this spring.

Yes, I think the throttle body does not ever fail and I have a Forman sensor on mine. I would check the wiring from the pigtail to the plug because those tend to come loose. The. I would check all the ground. The two big ones are on the back of the motor and they are pita to get to unless you have the intake manifold off. Also doing my grounding trick would help to. I kept all my grounds on for the heck of it since they were not hurting anything. Also the TAC module never fails either. It’s all in the wiring. I was also reading that it seems like 2003 is the year that seems to have this issue and some guy on another forum found that the wiring harness for the pedal and the tac module have a smaller gauge wire compared to a harness and pedal he took out of a 2004 plus truck. So GM fixed it with thicker wires on the later trucks.

I hope you figure out the problem I kept getting p1516 with this problem. Good luck!

I sporadically get that Tac and pedal sensor codes on my 03. I just clear the codes.

 

[mdmcinti]

I just got lucky and figured out that whoever installed the aftermarket pigtail harness didn’t do a good job crimping the connections. It took a little bit of trial and error, but wiggled the pigtail to cause the error code.

 

[OR VietVet]

Success!!!!!!!!!!!!

 

[clemenshess97]

Just did my ground wiring couple of days ago ,like in the youtube video (neg bat ->throttle body module ->firewall -> generator -> pcm), also cleaned the grounds near the front bumper and the two on the frame under the drivers door, replaced throttle body and replaced the pigtail connector, it worked for a few days.
But today I got P1516, P1518, P2108, P2135, also the doors unlocked and the ABS light came on, I cleaned the codes and it ran good for about 5 miles, then got P1516 again.
Does anyone have a idea what I can do ? add more grounds (from where to where) ?...I am kinda desperate now as I‘m driving to Denmark in three weeks and really want to get this problem fixed before heading on the Autobahn.

 

[rockola1971]

It’s holding up great. I put 10k plus miles on my Yukon after I found the root cause of my reduced engine power. It has not come back and it’s been almost four months. The truck is sitting now since it decided to have a lifter spin/collapse back at the end of December and take the cam with it. It runs fine and doesn’t miss, but it has horrible lifter knock and so it is parked until I get some money together to fix it this spring.

Yes, I think the throttle body does not ever fail and I have a Forman sensor on mine. I would check the wiring from the pigtail to the plug because those tend to come loose. The. I would check all the ground. The two big ones are on the back of the motor and they are pita to get to unless you have the intake manifold off. Also doing my grounding trick would help to. I kept all my grounds on for the heck of it since they were not hurting anything. Also the TAC module never fails either. It’s all in the wiring. I was also reading that it seems like 2003 is the year that seems to have this issue and some guy on another forum found that the wiring harness for the pedal and the tac module have a smaller gauge wire compared to a harness and pedal he took out of a 2004 plus truck. So GM fixed it with thicker wires on the later trucks.

I hope you figure out the problem I kept getting p1516 with this problem. Good luck!

Oh the throttle body "sensor" (TPS) does indeed fail. I bought my 2005 Yukon Denali at a discount from a car lot because it would go into limp mode immediately after leaving the parking lot and getting off idle rapidly during a test drive. I lowballed the used car place and told them I would take it as is and fix it myself. There were worn dead spots on the TPS. I replaced it for like $100 and works great ever since. Another fairly common problem is the wiring harness going to the TPS. It will get wire breaks a few inches from the plug causing intermittent open of a wire and loss of signal. In fact its common for the TPS to come with a new plug with wire harness that can be spliced to replace the OEM one. All cause immediate reduced power limp mode. All apply of course to drive by wire setups.

 

[clemenshess97]

I just realised I could make the engine go into limp mode and throwing all the codes by wiggling the small ground wire on the passenger side of the engine, turns out the wire was replaced already but the connection was made very poorly so it made the engine go into limp mode whenever I hit a hard bump. I cut the wire off and connected a new ground from the harness to the alternator bracket.
The terminal where it used to connect to the engine was still in good shape, but I wouldn‘t want to take this risk of this failing in the future, therefore I ran it to the alternator bracket, makes it easier to maintaine the grounds.

conclusion: new ground wire from battery to throttle body module, new ground wire from throttle body module to firewall, new ground wire from firewall to alternator bracket, new ground wire from alternator bracket to the PCM, new ground wire from the throttle body to the alternator bracket, new ground wire from engine harness ground wire to the alternator bracket and a new throttle body.

The amount of grounds are crazy, I know...but it runs fine now and doesn‘t throw codes when hitting hard bumps.
Maybe this helps anyone who is experiencing the same problems with his truck.
Good luck!

 

[OR VietVet]

So many times on these rigs intermittent or head scratching electrical problems are fixed by just doing something better than what the factory did.

That is why the Big 3 was thought of and developed: https://www.tahoeyukonforum.com/threads/another-big-3-upgrade-with-questions.111196/

How To: The Big 3

www.gmfullsize.com

 

[Monkeywrench78382]

so how has this been holding up for you? I am going to be diving into reduced power issues with our 03 denali soon. figured I would start with this type of thing before I start dumping things like throttle bodies and such at it. mostly because I am cheap!

Better bring your A game patience you're gonna need it, been fighting this issue for several days now, 750.00 in parts 12hrs of my time still unresolved. Sooooo mad almost set mine on fire! gonna see if I can find some answers if not just gonna dump it and it can be someone else's headache.

 

[bigdog9191999]

Better bring your A game patience you're gonna need it, been fighting this issue for several days now, 750.00 in parts 12hrs of my time still unresolved. Sooooo mad almost set mine on fire! gonna see if I can find some answers if not just gonna dump it and it can be someone else's headache.

Have ours solved for now. I started by adding several grounds just to be sure and because I had the parts so money was not a factor. But was unfortunately no change.

But it did end up being the tps, and swapped the tb and it fixed the symptoms. A few days of relearning and it hasn't driven better I'm some time.

Now is going to be on to oil pressure sending unit, and some o2 sensors.

Another reduced power thread 03 denali

well as the title indicates, having issues with reduced power on or 03 denali. I haven't done too much with it yet, but pulled some codes. a couple that I knew where there, and a couple that surprised me a little, but not too much if there is other electrical issues. guess it is time to get...

www.tahoeyukonforum.com

 

[Tonyrodz]

Mine randomly came on last week for 3 consecutive days when starting it in the am. It hadn't came on in a long while after cleaning the ground under the ds running board. I reset it each time and it was fine after that. It had those 3 common codes set too.