GMC general mess of crap help

[homersipes]

I have had my 2003 gmc 2500HD for almost 4 years now and have not had any real issues as far as driveability until a couple weeks ago.  we were headed to the store and it dinged at me and came up on the message center as "reduced engine power".  So I turned it off waited 30 seconds and bingo started back up and no issues.  all the gauges were where they should be, charging just over 14 volts, oil pressure 40 lbs, temp was around 150, wasnt totally warmed up yet.  so when I got home looked this issue up online and found its a DISASTER that seems to doom these trucks.  took the easy route and cleaned the throttle body, was pretty crappy, I used MAF cleaner on a rag to wipe the butterfly down and the throat as best as I could, there was a carbon ridge.  went almost 2 weeks and not a problem, thought it was just dirty.  Well yesterday on the way to work, did it again, same story pulled over.  got about 2 miles further and it did it again drove the rest of the way to work no issues at all, or on the way home.  so head to work today, jump on interstate cruising along at 70, with a big rig right behind me,BING "reduced engine power" and truck goes straight to idle, throw my 4 ways on damn near get rearended by tractor trailer, to the side I go.   now its irritating the crap out of me.  get to work scan for codes, get "1516 TPS out of range"  so thinking that the TPS is junk, go to part store for pricing, ummmmm cant get that have to buy entire throttle body he says.  okay before I buy it I figured would do more reading and testing.  I have read about guys replacing throttle body, pedal sensor, wiring pigtails, and even the engine, and STILL gets the same message.  So I found this site that tells how to test the throttle body and sensors
http://easyautodiagnostics.com/gmc/TAC/4.8L_5.3L_6.0L/resistance-tests/throttle_body_tests_1.php
went through and tested everything and the only 2 I had continuity through was C and A which is the TAC.  so if this test is accurate then my throttle body needs to be replaced, correct??    there is no rhyme or reason to when it does this, the wiring has been know to be fauly, so I started it up and wiggled every wire under the dash and under the hood and cant make it throw that engine power reduce crap, so I dont think its a wiring issue.  the only wires I havent checked is the grounds, will have to do that in the am, I am sick of looking at it.  have any of you had this issue, and do you think by the ohm test the throtle body needs replacing?  any help would be MUCHLY appreciated.

[Golfer]

Try LS1Tech forums too.

C5/C6 corvettes use a similar setup but different (similar) TAC modules and pedals.

This is a drive by wire setup not drive by cable setup on your LQ4 (6.0L?) right?  I have an intake manifold and some wiring off the donor LQ4 I'm using for my C3 engine swap and didn't really pay attention to what I pulled off since I wasn't using any of it. I'll be home on/about the 19th but LS1Tech might have some leads for you.

I wouldn't feel awful about using a salvaged throttle body if that's your problem and you should be able to find one cheap. I'm pretty sure the take off parts from mine are drive by cable but I'd need to look at it when I'm home to make sure.

[CAP1]

1. Run a redundant ground to the Throttle Actuator Control (TAC) module. A Black wire, pin 15.

2. Check for loss of B+ at the Pink wire, pin 7 when the problem happens.

3. Load test the wires using a high beam headlamp. Wiggle the harness and check for a glitch.

4. Take a snap shot using the scanner and check TP 1, TP 2 and Accelerator Pedal Position (APP) voltage values when the code sets.

::::EDIT:::
 i should add, that i'm assuming you've got the 6 liter VIN "U". check the eighth vin digit. that tells ya which engine ya have.

while not as common on gm products, as it was on fords, check ALL of the wires right at the connector for the throttle body, and the tac. i've run into a wire broken inside of the insulation, yet it looked perfectly fine on the outside, as the insulation wasn't even damaged. you need to kind of feel for it. you can feel the break inside the insulation, but it's hard.

 also, check ALL grounds, as even the seemingly unimportant grounds can/will wreak havoc on modern computer control systems. also....do you have access to a scanner, that you can leave hooked up, while you're driving? if so, go into datastream, and monitor the tps, accelerator pedal position sensors. set those parameters up to graph(very easy on the MODIS), and check those when the problem happens.

 hopefully some of that was helpful......

 :::EDIT AGAIN"""

 your parts guy was right. you cannot buy just the throttle position sensor. you need to buy the entire throttle body. check carefully though. some of these must be programmed to the vehicle, and aren't just a simple bolt on. i just had a customer spent nearly $800+programming on his volvo s80 after i'd diagnosed it for him.

[Golfer]

Or do that stuff ^^^^

[CAP1]

just checked. no programming required to r&r either of those.

[homersipes]

1. Run a redundant ground to the Throttle Actuator Control (TAC) module. A Black wire, pin 15.

2. Check for loss of B+ at the Pink wire, pin 7 when the problem happens.

3. Load test the wires using a high beam headlamp. Wiggle the harness and check for a glitch.

4. Take a snap shot using the scanner and check TP 1, TP 2 and Accelerator Pedal Position (APP) voltage values when the code sets.

::::EDIT:::
 i should add, that i'm assuming you've got the 6 liter VIN "U". check the eighth vin digit. that tells ya which engine ya have.

while not as common on gm products, as it was on fords, check ALL of the wires right at the connector for the throttle body, and the tac. i've run into a wire broken inside of the insulation, yet it looked perfectly fine on the outside, as the insulation wasn't even damaged. you need to kind of feel for it. you can feel the break inside the insulation, but it's hard.

 also, check ALL grounds, as even the seemingly unimportant grounds can/will wreak havoc on modern computer control systems. also....do you have access to a scanner, that you can leave hooked up, while you're driving? if so, go into datastream, and monitor the tps, accelerator pedal position sensors. set those parameters up to graph(very easy on the MODIS), and check those when the problem happens.

so to make sure I understand what you are saying here.
1. run a NEW ground to the TAC? to pin 15?  which pin is that, the only black wire there probably right?
2. when it cuts out, check for battery power to  the pink wire at the throttle body?
3. with the key ON check voltage at the connector on the throttle body?  I have wiggled and pulled on each wire while it is running and doesnt throw it into REP.
4. this one I am clueless on, not sure if the scanner we have can do that??
  yes its the 6.0 gas hog, and seems like everyone that has this electronic gas pedal crap has issues what ever happened to a throttle cable? never had issues with a cable before hahah.
and yeah gotta check all the grounds, havent done that yet.
thanks for input  seems like this is a very common issue but cant really get a fix on what happens, have read about guys taking their rigs to 4-7 dealerships and left with the same issue just without a few hundred dollars in their wallets.  hate to sa it but should have bought a toyota, as they stand behind their vehicle issues.

[CAP1]

so to make sure I understand what you are saying here.
1. run a NEW ground to the TAC? to pin 15?  which pin is that, the only black wire there probably right?Correct. don't eliminate the original ground. simply add your own ground to it
2. when it cuts out, check for battery power to  the pink wire at the throttle body?correct
3. with the key ON check voltage at the connector on the throttle body?  I have wiggled and pulled on each wire while it is running and doesnt throw it into REP.correct. the wiggling should eliminate the possibility of a wire broken inside the insulation. also, go back about 4-6 inches from the connector whilst doing the wiggle test.
4. this one I am clueless on, not sure if the scanner we have can do that??most scanners can do a snapshot. also, i'd forgotten to mention. check freeze frame data for that code failure.
  yes its the 6.0 gas hog, and seems like everyone that has this electronic gas pedal crap has issues what ever happened to a throttle cable? never had issues with a cable before hahah.
and yeah gotta check all the grounds, havent done that yet.
thanks for input  seems like this is a very common issue but cant really get a fix on what happens, have read about guys taking their rigs to 4-7 dealerships and left with the same issue just without a few hundred dollars in their wallets.  hate to sa it but should have bought a toyota, as they stand behind their vehicle issues.

 they went to electronic throttles, as it's much easier to intergrate the traction control, abs, and stability control this way. the computer will actively back off on your throttle under certain conditions.
 stay away from dealerships. find a local momandpop shop that's got a decent rep for diagnostics. they'll find it faster.

[homersipes]

thanks for input was up until 3am reading on this, 1 guy replaced, the foot pedal, throttle body, all the pig tails, grounds, and even pcm and it still does the REP.  seems to me from what I have been reading once it starts this there really is no cure to fix it.  the code 1516 has SO many things it can be, and I cant find much on the 1516 TPS out of range. from what I know and been told if its out of range its junk, but its so friggin intermittent, I guess its like having a code pop up, erase code good for a couple days before it comes back on. so to check the voltage when it does this, do I need a piercing probe to probe wire and check to ground?  there have been hundreds if not thousands of these rigs with the same exact issue GM should stand behind it and repair this before someone gets killed, I couldnt imagine being out west, hauling a camper trailer and having it do that, no place to pull over and not enough power to do anything.  It is a pretty scarey feeling when it does it on the interstate.  will never buy another one, I like the 90s gmc trucks, simple easy to work on.

[Slate]

   Hope this helps.....

Customers may have a concern of lack of power and engine light on. DTCs set will almost always contain a P1518 and may contain any of the following (P1516, P2108, P0220, P0120, U0107). An improperly torqued TAC module ground may be at fault. The Ground is listed as G104 on TAC module schematic which is incorrectly labeled on SI document ID 855376. The correct ground is G103. The locator for SI states that G103 is located on the left hand side which is incorrect. However, there have been field reports stating that G104 has also corrected this condition. G104 is a horizontal bolt in the rear of the left head and extremely difficult to reach. G104 should also be tightened at the same time.

There have also been field cases where ground G110 on the outer drivers side frame rail caused a P1518 code and an intermittent connection at splice 102 on the intake.

All published SI diagnostics should be followed in addition to following the recommendation listed.

Recommendation/Instructions:
Tighten ground G103 located behind the right cylinder head (passenger side) just below the head and mounted into the block. The ground uses a 13 mm bolt head mounted vertically to the engine block just above the bell housing.

 

Models:
(03 Chevrolet Silverado 2WD, 4WD) and (03 GMC Sierra 2WD, 4WD) and (03 Chevrolet Tahoe 2WD, 4WD) and (03 Chevrolet GMC Yukon 2WD, 4WD) and (03 Chevrolet Suburban 2WD, 4WD) and GMC Yukon XL 2WD, 4WD

  There is also a ground below the drivers door on the frame rail that should be checked. Also the pigtail to the throttle body should be inspected as the wire can be broken inside the insulation. Gently pull on the wires. if the stretch and break easily replace with a service connector that has new wires already installed.

  A good technician will not replace parts until he finds the problem. 

[homersipes]

  A good technician will not replace parts until he finds the problem.  rolleyes

so true    I dont like throwing parts at vehicles, and this is hard to pin point the cause, because it can be soo many things.  going to see if my buddy will help me tonight chase wires and grounds, figure 2 sets of eyes is better than 1.

[CAP1]

you can also use a dvom, or a scope and sweep the tps if you suspect that. you should be able to do the tps, and the accelerator pedal position sensor with koeo. do the sweep very slowly, and watch for voltage to go wonky, or if on a scope, it'll drop for a split second.
 always test these things koeo. forget about using resistance. too much chance of erroneous readings.

[homersipes]

okay so a dvom is a digital volt meter right? lol and how do I do a sweep?  sorry never had to deal with this crap before, anytime had to replace something as far as sensors, pull code, replace sensor.  have had to figure out basic wiring before but as I said never to this depth.  koeo is key on engine off right?  so to do this test, would I unplug each plug and test each wire, or can I probe the back of the plug and test for volts?  sorry need this crap spelled out for me  this is why I hate new vehicles, older rigs, gas, spark, compression, and air, easy new trucks  suck!   I have done the wiggle test to the whole harness and get no REP, so I am thinking that it HAS to be the pedal, or throttle body.  havent done the grounds yet going to take it to my buddies house later and maybe both of us can figure something out.  so what steps would you take at approaching this?  seems like the wiggle test eliminates wires broken, so I would need to check the grounds, then do the sweep that you were talking about.  if you could instruct me on how to do this would be awesome

[CAP1]

okay so a dvom is a digital volt meter right? lol and how do I do a sweep?  sorry never had to deal with this crap before, anytime had to replace something as far as sensors, pull code, replace sensor.  have had to figure out basic wiring before but as I said never to this depth.  koeo is key on engine off right?  so to do this test, would I unplug each plug and test each wire, or can I probe the back of the plug and test for volts?  sorry need this crap spelled out for me  this is why I hate new vehicles, older rigs, gas, spark, compression, and air, easy new trucks  suck!   I have done the wiggle test to the whole harness and get no REP, so I am thinking that it HAS to be the pedal, or throttle body.  havent done the grounds yet going to take it to my buddies house later and maybe both of us can figure something out.  so what steps would you take at approaching this?  seems like the wiggle test eliminates wires broken, so I would need to check the grounds, then do the sweep that you were talking about.  if you could instruct me on how to do this would be awesome

 correct....koeo is key on engine off. do not disconnect the connectors. backprobe into the back side of the connector. you need to identify the signal wire, and the ground wire. to do a sweep, you're simply working the throttle pedal. very slowly you'll depress the pedal, watching the voltage reading. i think this one will go from about .7Volts up to about 4.9volts. that should be the tps. the accelerator pedal position sensor often goes opposite the tps, so you'd look for about 4.9v down to about .7v.

[lunatic1]

u can save time and money--if you just take it to the gm/gmc dealer-which has the right equipment-to run diag's and the diesel tech's have more than likey see your problem before....just sayin..goodluck

[CAP1]

u can save time and money--if you just take it to the gm/gmc dealer-which has the right equipment-to run diag's and the diesel tech's have more than likey see your problem before....just sayin..goodluck

 the problem with dealers is that the good guys that would be able to figure it out don't want to work on it. they want the gravy jobs. accordingly the guys that don't know, or are learning get the job. and you end up spending more money to figure it out.

 there is very little from any of the domestic manufacturers that us private guys can't figure out.