03 Sierra Throttle By Wire......

bbnate804 · April 28, 2010

have been having trouble with my 03 2500hd 6.0 for about a year and a half now. i've read all the info i can online and have had two different dealerships work on the truck. just haven't been able to shake the "reduced engine power" gremlin. initially it was reduced engine power, check engine light, codes were 2135 and 1516. the dealership cleaned the throttle body. it came back again within a week so they replaced the throttle body. about a month later deja vu, the dealership did the pigtail swap. in the next few months they would end up replacing the throttle body and pigtail again. the truck was alright for a few months then winter hit and back to the same old. this time they "diagnosed" the issue and determined to repair the issue they would run a new wire from the throttle body to the pcm. this repair lasted the longest. here in the past month i've had intermittent events with the truck and the reduced engine power. going down the road it'll kick the lights and give me a 2135 code only. then there are times when i get in the truck and go to start it and the engine lights are on. if the check engine lights on before i start the truck i get codes 2135 and 0120. 2 throttle bodies, 2 pigtails, one new wire, and a new accelerator pedal (installed by me)... any thoughts? whats the difference between the 1516 and 0120 codes?

tahoesub1 · April 28, 2010

have been having trouble with my 03 2500hd 6.0 for about a year and a half now. i've read all the info i can online and have had two different dealerships work on the truck. just haven't been able to shake the "reduced engine power" gremlin. initially it was reduced engine power, check engine light, codes were 2135 and 1516. the dealership cleaned the throttle body. it came back again within a week so they replaced the throttle body. about a month later deja vu, the dealership did the pigtail swap. in the next few months they would end up replacing the throttle body and pigtail again. the truck was alright for a few months then winter hit and back to the same old. this time they "diagnosed" the issue and determined to repair the issue they would run a new wire from the throttle body to the pcm. this repair lasted the longest. here in the past month i've had intermittent events with the truck and the reduced engine power. going down the road it'll kick the lights and give me a 2135 code only. then there are times when i get in the truck and go to start it and the engine lights are on. if the check engine lights on before i start the truck i get codes 2135 and 0120. 2 throttle bodies, 2 pigtails, one new wire, and a new accelerator pedal (installed by me)... any thoughts? whats the difference between the 1516 and 0120 codes?

Wow, my 2003 1500HD with a 6.0 just started doing this. Checked wiring and grounds and could not duplicate. I had code 2135 and 0120. Replaced throttle body and pedal. OK so far, but only been a couple of weeks, so your post is not inspiring..... So my thoughts are there is more than 1 wire that can cause the issue. Most popular is the yellow (Pin A in attachment), but i think one of the browns, Pin C, does the same as the yellow. All drive by wire systems have redundant backups, meaning there are two sensors on each side and they must always agree to give you full throttle control. When they don't, it goes into reduced power to ensure you don't lose control. Also, I think 1516 relates to the Throttle Actuator Control (TAC) Module. This is the box in the top drivers side corner of the firewall and has two plugs on bottom of it. This is the brains of the drive by wire system. There are two grounds G103 and G104 in the rear of the engine behind the intake module, see attachment Check these. Wiggle and grab all wires between TAC and Pedal and TAC and throttle body. A bad wire may duplicate the REP if manipulated. If these are good, the TAC module may be next. Good luck and please keep us posted...

bbnate804 · April 28, 2010

appreciate the response. you may have better luck then i've had. i've yet to find anybody else who's had as much trouble as i've had. the dealers thought for sure that the throttle body and pigtail would catch it but no such luck. the fact that the one code has remained the same and the other changed should help some in a diagnosis. my fear at this point, is with all the work thats been done, the wiring has been hacked too much to be repaired without doubt. is the throttle wiring an independent harness or is all the under hood wiring one big harness? some of my research has indicated a special crimping tool is needed when splicing wires for the throttle body, any truth to this?

98 Z71 SLT · April 29, 2010

I had similar codes on my old 2006 Sierra, and a simple pcm reprogram fixed SES light and throttle codes

Go to your dealers with Bulletin 06-06-04-042B, and give that a shot

mephisto · April 29, 2010

I have a 2004 2500 non hd and had the same sort of problems. Tech told me there was a recall on the harness going to the throttle body.

tahoesub1 · April 29, 2010

appreciate the response. you may have better luck then i've had. i've yet to find anybody else who's had as much trouble as i've had. the dealers thought for sure that the throttle body and pigtail would catch it but no such luck. the fact that the one code has remained the same and the other changed should help some in a diagnosis. my fear at this point, is with all the work thats been done, the wiring has been hacked too much to be repaired without doubt. is the throttle wiring an independent harness or is all the under hood wiring one big harness? some of my research has indicated a special crimping tool is needed when splicing wires for the throttle body, any truth to this?

I have heard of the entire engine harness being replaced to correct. Not sure of what special tools are needed to crimp these specific wires. I am crossing my fingers for now on mine... If I were in you position, I would do all of the wiring and ground checks and if nothing found, replace the TAC module. Keep us posted!

nickvrebel · April 29, 2010

if it doesn't cause any other issues I'd just whip out HP Tuners and turn the codes to "no error reported" and go on with life.

bbnate804 · April 30, 2010

this is the first time i've heard anybody mention reprogramming the pcm. what'd the deal charge to do the programming? anybody have part numbers for the harness and tac module? i struggled trying to pin it down with partsdirect online. there is one thing that i did forget to mention when listing my symptoms. i couldn't tell it before but its easy to pick out now with dual exhaust. sometimes with the cruise on or just holding the pedal steady going down the highway. i can catch the truck surge or lag on the throttle not hardly a second and prob not even 100rpm difference. not long behind comes the reduced engine power and check engine light. i don't know if that makes a difference or not. it doesn't happen often and it doesn't have to happen to trigger the lights.

tahoesub1 · April 30, 2010

this is the first time i've heard anybody mention reprogramming the pcm. what'd the deal charge to do the programming? anybody have part numbers for the harness and tac module? i struggled trying to pin it down with partsdirect online. there is one thing that i did forget to mention when listing my symptoms. i couldn't tell it before but its easy to pick out now with dual exhaust. sometimes with the cruise on or just holding the pedal steady going down the highway. i can catch the truck surge or lag on the throttle not hardly a second and prob not even 100rpm difference. not long behind comes the reduced engine power and check engine light. i don't know if that makes a difference or not. it doesn't happen often and it doesn't have to happen to trigger the lights.

Curious on your observation, I noticed since I have owned the truck that the throttle surges 100-200 rpm in cruise control going down hills. No surging on flats or uphill??

Not sure of the PN for the harness. The TAC module is either 12573059 or 12588923. The 3059 is the PN on my TAC module, but does not come up on the gmpartsdirect site. Partszoneonline takes you to the 8923 PN when you search the 3059. Googlling around shows the 12573059 for 03-04 and the 8923 for 05 and up. Best to give your vin to a dealer and see what they come up with. You could even try a wrecking yard to see if they have a module from a wrecked 2003-2004.

As far as reprogramming, call Justin @ Black Bear Performance. I did the data logging tune, and it worked out great. We found a leaky intake manifold and the MAF going south prior to any major failures. Truck runs way better, and got 1-1.5 mpg better, along with better shifts and defintely more power. http://www.blackbearperformance.com/ I kept my stock pcm and he programmed and shipped out a replacement with the new tune. Good luck!

redvett · April 30, 2010

Here is a service bulletin from GM.

Service Information

2003 Chevrolet Chevy C Silverado - 2WD | Sierra, Silverado (VIN C/K) Service Manual | Document ID: 1869994 #PIP3089B: SES Light And Reduced Engine Power DTC P0120 P0220 P1516 P2135 - keywords accelerator actuator APP blade body connector connection DTC L33 L59 LH6 LR4 LM7 LS1 LS2 LQ4 LQ9 module position reduce sensor - (Oct 31, 2006)

Subject:SES Light and Reduced Engine Power DTC P0120 P0220 P1516 P2135

Models:2004-2006 Buick Rainer

2005-2006 Cadillac CTS-V

2003-2006 Cadillac Escalade

2003-2006 Chevrolet Avalanche, Corvette, Express, Monte Carlo, Silverado, SSR, Suburban, Tahoe, Trailblazer

2003-2006 GMC Envoy, Savana, Sierra, Yukon

2003-2006 Hummer H2

2005-2006 Pontiac GTO

Equipped with a 4.8 5.3 6.0 or 7.0 V-8 Engine

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

A vehicle may be brought into the dealer for a reduced power message, and DTCs P0120, P0220, P1516, P2101, or P2135.

The Throttle Actuator Control (TAC) / throttle body type trouble codes, may be caused by a loose wiring crimp at the throttle body connector, or a broken throttle body circuit.

Recommendation/Instructions:

Complete the current SI diagnostics for any symptoms or trouble codes found. If a intermittent T/P or TAC module type code is occurring complete the inspections below.

Inspect all related throttle body terminals for a loose wiring crimp. The loose crimp may be difficult to find, and the poor connection will be between the terminal and the copper strands of the wire. Wiggle test the individual throttle body circuits to see if the concern can be duplicated.

Inspect the related circuits for broken wires inside the insulation. The outer wire insulation may look fine, but the internal copper strands may be partially broken. Breaks in the wires usually occur within 1 to 4 inches of the throttle body connector. Wiggle testing may also induce a trouble code to set.

On C/K trucks complete SI procedures for voltage drop on grounds G103 and G104. Grounds G103 or G104 may be loose or corroded.

If a terminal crimp or a broken wire has been found, repair or replace only the circuits involved. There is a throttle body pigtail connector available through GMSPO, but installing this pigtail connector may cause other intermittent TAC module/TP codes at a later date. If this pigtail must be used, please follow the SI procedures for Splicing Copper Wire Using Splice Sleeves. (the proper Kent-Moore crimping tool must be used for this repair)

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

samy1969 · December 20, 2010

I just got this error code as well, plus a couple extras:

P0120 - Throttle Positioning Sensor

P0171 - Fuel Trim Bank Two Condition

P0174 - Fuel Trim Bank One Condition

P2135 - APP Sensor 1 and APP Sensor 2 signal voltage fault

When the reduced engine power error is thrown, how long do you have to wait before you can drive the truck again? I am asking because the truck is my only vehicle and I don't know if I should continue driving it or if I should take it in for service and rent a car in the meantime. I can handle a couple of minutes for the truck to reset itself before allowing me to drive again, but what has your experience been in the amount of downtime when the reduced engine power message is thrown?

Sam

[email protected] · December 22, 2010

yep, my dads truck is sitting out back collecting snow while hes driving around a rental car, cuz his truck is having the same issues. we replaced the gas pedal assembly, and it worked for a little while, but still does it. he hates to have to bring it to the dealer to get it fixed, especially since all you guys have had the same problem, but cant seem to find the cause.

[email protected] · February 1, 2011

my dads truck is 2 for 3. replaced the gas pedal assembly, and the throttle body harness, and re crimped them. thought it was fixed, but its not. so now the dealer has the truck again and they're not sure what they are gonna do. replace the throttle body i guess. i told my dad to get into an accident because of the reduced engine power, then sue GM,,,just like what everyone was doing with Toyota.