reduced power mode

Typically, what triggers the system to go into limp home(reduced power) is a fault that relates to the throttle actuator or accelerator pedal position assembly. Ideally, you should seek the trouble code that is associated with it. One crucial concern, is does it have any aftermarket stuff installed? There may be a bulletin that states(depending on the code) the throttle body or body connector could be cause, and it could be. I have seen instances where this was followed, only to have the fault reoccur, and it eventually was ruled to aftermarket installations into critical circuits. The electronic throttle is run on 5 volt potential, so some resistance that would go unnoticed in a 12 volt circuit, causes intermittent problems in a 5 volt circuit.

There are no after market items on the engine. I will get a code readerand post that in a few days.

Okay, I got a scanner and the two codes that are popping are P1516 & P0171. Should I remove and replace the throttle body or is there a check that I can do before I go out and spend $200.00 for that part? Thank you for your help!

The P0171 is a lean code for one bank of cylinders. It would not result in a reduced power message. I would clear it and see if it returns over time. The P1516 will result in reduced power. There is a bulletin I included for reference, may or may not apply, but gives a starting point.

#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




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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).
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The test chart for that code involves some circuit testing, and may be most streamlined with a scan tool that can display data. Often times this code can be hard to duplicate. If I were to start somewhere, it would be splicing a new connector at the throttle body.

I had the same problem and found two broken wires 3/4" from the throttle body plug. Two butt connectors and back in business.

Thanks for the heads up Chief_FI.

Flyboy did you ever get this diagnosed and fixed, or do we need to do more testing and diagnosing?

My 2003 Silverado 2500HD 6.0 has a "service brake booster? message in the DIC - how can I reset it? I don't believe there is a problem as everything works great! Thanks for your help.

Please post your question here

https://www.2carpros.com/questions/new

Cheers, Ken

2003 Chevy Silverado 49,000 miles. Went to start the truck in the morning and the reduced engine power warning came on in the DIC. Manual says it comes on due to overheating and enters coolant protection mode. When I press the gas the truck will not accelerate. How does it have a overheating problem sitting overnite and how do I get it to a garage if it only idles down the road? Is there a reset button so I can at least drive it?

did you check coolant level?

Had the same problem with my 05 Z71. Took it to the Chevy dealership and turns out it was a broke wire. Auto Zone scanners wouldnt read it when I took it there due to a blown fuse. Have someone check all the wiring before you spend mega bucks.

If while cranking I get a 1 second stutter I get the above codes but if the cranking continues normally it then starts and runs fine. I've cleaned the ground under the driver, checked the ohms at the TPS and accelerator, did the tug test and checked for corrosion on the TPS connector, checked the wires in the fuse box (left fender), cleaned and charged battery, and checked and cleaned the throttle plate.

check your ect sensor might be part of problem and check for broken wire
at throttle body and firewall it rubs on there and wears through. it'a blue and white wire. you may need to replace the throttle body as well which is pricey.also check the ground wire at back of lh head and give a tug the eyelet likes to break there just a soft tug will do it.

How do I test the ECT?
Is there any test on the throttle body?

on chart in pic one side is temp and other is ohms so check it that way lh side is temp. see pic for other app is the gas pedal

I did find cracked insulation on a gray or brown wire in a harness between the fuse box (left fender) and a 3 x 4" black box mounted on the firewall. When I tugged on it it parted so I spliced it with crimp style connectors reset the codes and drove it for 25 miles. So far so good. Thanks for the help, I'll get back to you if it reoccurs soon.

the crimp style connectors should never be used on vehicles now a days. you should only use solder type connections with shrink tube to protect them.. glad you found the problem.

At highway (55 and up) speeds the reduced engine power reading comes on and shuts down my power.I have to pull to the side of the road shut off the truck, wait 10 seconds, then it'll start back up normal. The U0107 code appears stating loss communication with throttle actuator control.i have replaced the wiring harness and throttle position sensor as i heard this may be the problem. I have also cleaned the throttle body. Neither seemed to work. What could this be?

tht is the throttle control module-gas pedal in laymens terms. check battery for condition as this can cause it also do a load test. tire stores auto parts do for free. then see if terminal ends are corroded on gaspedal if you are in the winter climates. you shold also get it scanned first too to see if other codes are set as they may set this one. finally check gas peadal to see if it is shorted out or not sending correct voltage to pcm.

The only other code showing up is show loss of communication with electronic brake control module which I don't think should have to do with the throttle actuator control. And the terminals on the battery are clean

I am not sure what's been replaced on it. I bought the truck 3 weeks ago and it didn't start occurring until the day after buying it. The day I bought it I drove it home (300miles) with no problem. Then it started happening the day after and I haven't been able to narrow it done. I will have the battery tested tomorrow though to check it's strength.

From Jacobandnickolas
Apr 23, 2014.

U0107 can set if the battery voltage is low. Check to make sure that isn't an issue. Also.
It can also set if there is a short to B+ on the TAC module ground circuit.Check fuses for the circuits that are in the TAC module harness. Finally, this code can also be set if the TAC module ignition feed circuit is shorted to a B+ supply circuit. When the ignition switch is turned on, the TAC module is powered-up before the PCM. The code sets because no communication is detected by the TAC module from the PCM. You will need to check circuits for being shorted to a B+ supply.

The check engine light came on and reduced engine power came on, it slowed down and couldn't press the gas. I turned it on a min later and the truck is running fine. What could be the issue

scan for codes first it may say what area to check

Yes sir. It didn't say where to check just the code P1516

sorry my goof id didn't read that part in header. low voltage causes this so check battery for condition including load test as well as dirty terminal ends on battery . Also check belt and tensioner as it may be slipping recommended replacement is 60 k for both. finally cleant throttle plate on both sides and iac hole with choke cleaner. If battery is disconnected you may need to reset anti theft. if it continues a pro will have to check this to see If the calculation is correct between actual throttle position as well as calculated position because that is what this code is.

enter your question...My 2003 2500 siverado check engine light comes and display's reduced engine power. When it happens it slows down and a dinger goes off and as we pull over, the truck shakes violently. After the engine has been off for about five or ten minutes, then it seems to be fine but then may start all over again. I've driven straight away to the Vern Ide in Lewiston Idaho while it's happening and leave it running so the mechanic can get the code and he said he could not get it unless it happened while he had it. But when I've left the truck with them it never happens. Traveling from California to Idaho the truck did this more than thirty times! Turned a two day trip into a very stressfilled three day trip...been going on for six months now! Any ideas? Thanks!

To fix the problem is very easy but first check the wire at the throttle sensor make shore it not a loose wire. It will cost about $130.00.U will need to buy a accelerator position sensor, for a automatic 03 u will have to get it from the dealer, for manual 03 u can get from a part store.Once u get the A.P.S put it on disconnect the battery, if it does it again, plug in a piagnostic machine and then erase the codes to reset the computer.That's how i fix my 03 silverado.

Make shore the check the engine light is on while getting a diagnostic thats how u get the code.

no power at gas pedal have codes p0120 -p0220 -p0758 -p1516 -p1518 -p1860 -when i clear codes they come back

You may have one or two problems here, try removing Ground G103 on the back of the cylinder head, clean both the mating surface and the wire end, use emory cloth and get it nice and brite, re attach ground and cover with RTV. Let me know if this helps, here's the GM TSB on it:
CHECK ENGINE LIGHT ON WITH NO DRIVEABILITY CONCERNS, DTC P0120, P0220, P1516, P1518 (CLEAR CODE) TECHNICAL SERVICE BULLETIN Reference Number(s): 03-06-04-032, Date of Issue:  June 16, 2003 Related Ref Number(s): 03-06-04-032 ARTICLE BEGINNING CONDITION Some owners may comment that the Check Engine Light is illuminated and there is no driveability concern. Upon investigation, the technician may find codes P0120, P0220, P1516 or P1518. Also, technicians may note that low voltage codes P0562, P0563, P1637 or P1638 have been set. CAUSE The Tach module may set the code in error if it operates at a battery voltage of 4.5 to 5.0 volts. CORRECTION If the vehicle has stored one of the low voltage codes, P0562, P0563, P1637 or P1638, follow the appropriate diagnostics for the low voltage code. In most cases, this will lead to correcting the concern without replacing any Electronic Throttle Control (ETC) components. If codes P0120, P0220, P1516 or P1518 are present without any of the low voltage codes, the technician should observe the Engine RPM in the fault record.  If the Engine RPM in the fault record is zero and the customer indicates that the vehicles has experienced a low voltage condition, the code should be cleared and the low voltage should be diagnosed and corrected.  If the Engine RPM is zero and the customer indicates that there have been no low voltage conditions, then the P1516 diagnostic aids for intermittent concerns should be used to diagnose and correct the vehicle.  If the Engine RPM is greater than zero, then check for an obvious loose ground at G103 located next to the right cylinder head just below the head and mounted into the block. Also, check G104 located behind the left cylinder head. Then verify all electrical connections at the TAC module. If the concern is still not resolved, contact Technical Assistance. CADILLAC: 2003 Escalade, Escalade EXT, Escalade ESV with 4.8L, 5.3L or 6.0L Engine (VINs T, N, U - RPOs LM7, LQ9, LQ4) CHEVROLET: 2003 Avalanche, Silverado, Suburban, Tahoe with 4.8L, 5.3L or 6.0L Engine (VINs V, P, T, Z, N, U - RPOs LR4, LM4, LM7, L59, LQ9, LQ4) GMC: 2003 Sierra, Yukon, Yukon XL with 4.8L, 5.3L or 6.0L Engine (VINs V, P, T, Z, N, U - RPOs LR4, LM4, LM7, L59, LQ9, LQ4) SECTION: 06 - Engine/Propulsion System

thank you merlin ground cable seem good and intacked should I disconnect really and clean 617-775-8180 john

pulled off ground and cleaned it also have code p0758 also when try to erase codes they sometimes come right back also sometimes truck will not shut off when you turn off key lights on dash flicker and motor stays sputtering once I put on lights and it shut off whith key in off position of coarse hellp jmn needham

[quote:5447e7debf="jmnneedham"]thank you merlin ground cable seem good and intacked should I disconnect really and clean 617-775-8180 john[/quote:5447e7debf]

won't be at my computer till afternoon but will be at truck wait'd for response on sunday desperatly you can callme 617-775-8180

heyyy, anyone there same problems

I was asked to assist-check all wiring connections on the PCM if okay have the PCM tested or get it flashed and see what happens-you got too many codes could be one and throwing off the others

You can try testing the throttle position sensor and manifold absolute pressure sensor

I had a major 2 drive computer crash, wish I could pick these pieces up like I can with cars... sorry, to further help I need the engine size in liters, 1500 HD?
Diagnise the P0758 code, and check with Chevy on these others, this group of codes is for several problems, but is supposed to be harness and or ground related. Did you check for ground strap and battery negative connection to the block as well, Might be worth a shot.
P0758= Short to ground or open in + in the 2-3 shift solenoid circuit, so check the wiring harness at the transmission for a good connection and for water intrusion in the connector.
Thanks for the help Jess, I was completely down for a few days, slowley getting off the mat!
Reinstalling all my gear.

I have a 2500 hd chevy when i start it,it goes start into reduced power or limp mode i kill it and wait then start it back up it will run fine until i touch the gas peddle then it will go back into limp mode. I have a code reader and i can clear it with that sometimes but most of the time i have to kill it and wait. I have changed to throttle body and throttle body position censor and the peddle position censor multiple times and it still does it i have changed ecm and my computer flashed to where it didnt even know the code and it still goes into limp mode. I have took a cuircit tester and tested all the wires from the peddle to the computer and from the computer to the throttle body and came up empty. So any info would be helpful .

I would start by getting it scanned at a chevy or gmc dealer, although it will cost money, they can read the ignition switch actual and read positions, this sounds like an ignition switch issue.