Reduced Engine Power

dwilliams · April 24, 2005

I have a 2002 Chevrolet 2500 HD 8.1L Allison 4X4. Last weekend our family took the first camping trip of the year. When I returned I unhooked the truck from the camper (but did not move it) and left for the rest of the week on company travel. My wife started the truck up on Friday and the message center reported "REDUCED ENGINE POWER". The service engine soon light was on and when she pushed the pedal down the engine would not rev up at all. I was due home today so she just turned it off and left it. I first checked all the fluid levels and saw the coolant was a little low. I filled the coolant to the mark and started the truck. Same message. I can't drive the truck to the dealership because it will not accelerate. The owners manual says things about overheating. It displays this message when the truck is cold. I have only ran the engine for about 10 seconds so I don’t think I have hurt it but I need some help on where to even start. Sensors or tow trucks?

dwilliams · April 25, 2005

Ha! I went to the dealership and saw many things on the mass flow sensor in the service bulletins. Other than that they wanted to hook it up to the computer. I unhooked the battery to see if that would clear the code and checked the air filter. It has never been replaced. A mouse had built a nest inside the airbox. After I cleared this out and hooked the battery back up, I still had the message and srevice engine light. I started looking for more signs of the rodent and found a wire broke (chewed) on the throttle body. I repaired this and the throttle began to respond and the reduced engine power message went away! The service engine light is still on, probably another che... broken wire. Thanks to everyone that took the time to read the post anyway. I'll be checking this site more often.

mudbug660 · April 26, 2005

I love rats. had some get in my yamaha grizzly and ate a bunch of wires. they built it right where the transmission intake is. Go figure.

lundgren · July 8, 2007

Ha! I went to the dealership and saw many things on the mass flow sensor in the service bulletins. Other than that they wanted to hook it up to the computer. I unhooked the battery to see if that would clear the code and checked the air filter. It has never been replaced. A mouse had built a nest inside the airbox. After I cleared this out and hooked the battery back up, I still had the message and srevice engine light. I started looking for more signs of the rodent and found a wire broke (chewed) on the throttle body. I repaired this and the throttle began to respond and the reduced engine power message went away! The service engine light is still on, probably another che... broken wire. Thanks to everyone that took the time to read the post anyway. I'll be checking this site more often.

At least it happened when you weren't driving it! Mine did it today loaded with my travel trailer going up I-70 in the Rockies! After towing it home and a friend towing my trailer home it is all happy with the engine codes P1515 and P1516.

Dave_085 · October 21, 2007

Check the yellow wire on the throttle body.. even if it doesnt look broke .. feel under the yellow covering the wire might be broke under.. at least it was on my 03 2500 hd

Dave

Nytemare · October 21, 2007

wow...this post is only 2 years old...

chipjumper · December 31, 2007

Dang I just bought a used 2003 Sierra in Vermont and had to drive this sucker to Michigan. It kept stalling randomly with that silly "reduced engine power" message. The guy I bought the truck off of claimed that it never has done that before but he conveniently provided me with a portable code scanner that I could delete the code with and proceed with my 800 mile trek. I should also note that the truck had a terrible idle and would stall at red lights.

I took the throttle body off and it was full of gunk. I used STP throttle body & intake cleaner to clean every part of it. I also used that CRC MAF sensor cleaner and disconnected the battery for about 2 hours to clear the PCM. Put everything back together and started her right up and it idled perfectly. I could shift it into gear and it wouldn't even hesitate.

Took it for a test drive and about 2 miles later it stalled with that stupid reduced engine power. I noticed that if I do not shut off the engine --- just let it run like crap (owners manual says that its running on reduced amount of cylinders) and I clear the codes via the portable code scanner the truck immediately runs fine.

This problem, at least for my truck, must be attributed to some sort of electrical problem. It has to be some sort of trigger that sets the P1516 code just for a split second. I'm scared to drive this truck knowing that it could die at anytime, anyplace.

So far I have seen the following "fixes"

-Bad Grounding (connector? grounding straps?)

-Replace throttle body & upgrade PCM software

chipjumper · January 2, 2008

Okay, the next day I checked the engine ground -- cleaned and tightened the contacts. I cut and soldered a new yellow wire to the TAC (throttle actuator control --- throttle body)about 10 inches long starting about a half inch from the connector. Still got the P1516 "Reduced Engine Power". I went to a local Chev dealership and the service writer knew exactly what I was talking about. He recommended a PCM update before proceeding. He also consulted with a tech who said that a PCM update usually solves the problem but on 2003's it may also need a new TAC. They were closing early cuz it was New Year's Eve so I had to leave without getting the update ($85). I'll go back later for that.

I did go out and buy a new TAC. I went thru an auto shop that I worked at for a few years out of high school. Luckily I can buy parts through them for wholesale cost. A nearby GM dealer wanted $195 (wholesale cost to auto-service, regular price is like $250). My old boss recommended Rowerdink (local GM Part wholesaler) who priced it at $135. I couldn't turn that down.

Installed the new t-body/TAC and since then I've put on about 200 miles and I haven't had one hiccup. I suppose that the 160,000 miles have beaten up the original TAC's stepper motor and it must have been a hair off compared to the TPS readings and therefore setting a code. I suppose I should be happy that GM has this "safety function" so if my TAC goes haywire I won't be running over a pedestrian (unlike the Ford's when they first used electronic throttle's)

Solution - Replaced electronic throttle body "TAC"

Cost - $135 + tax

Time - 20 minutes