2003 GMC 2500 HD 8.1L need help with cruise control wires - The 1947 - Present Chevrolet & GMC Truck Message Board Network

pound41 · 11-16-2020, 11:06 AM

Hello I have a 2003 GMC 2500HD 8.1L goes into reduced engine power
PO2135. Everything has been swapped out with new GM still does it. I am getting a new harness made. I have to give the builder lengths for the wires. I cannot find the path for the cruise control wires to the column. are they 1 long wire or do they go into the ecm and another wires comes out? any help is greatly appreciated

ls1nova71 · 11-16-2020, 11:38 AM

The 8.1's in that year were wired like an LS engine, the cruise wires come out of the TAC module, there are three of them. THat said, throwing a harness at that problem is just throwing money at the problem. What all have you replaced? It sounds like its most likley the gas pedal/sensor.

pound41 · 11-16-2020, 05:44 PM

Everything has been replaced with new GM. I bought the truck new. I had it a few weeks. one cold morning I started it up it drove fine went to the store to get morning coffee. Came out started it up the truck shook I read the Reduced Engine Power. turned it off restarted it and it started right back up. I called the dealer and told them what had happened. They said if it does it again bring it back in. Over the next 16 years it would occasionally do just that. In 2019 it started getting more frequent and taking more times to start. The connector and wire leads at the throttle body were replaced because TP1 had the 5 volt reference and TP2 was at 4.2. After that for the first time in 16 years in went into REP while I was driving it. Changed the throttle body good for a week then REP. TAC module good for a few weeks then REP. ECM good for a few weeks then REP. Pedal assembly was changed went into REP after about 15 minutes of running in my driveway. Took it to the dealer they replaced some pins at the TAC connector good for a few weeks then REP. I had thought the connector at the TAC module was the issue. So I swapped in a new one good for a few weeks then REP.

**Hidesertchevy** · 11-17-2020, 10:30 PM

I had the same problem ended up being broken wire inside insulation at the intake throttle body harness plug. Same reduced engine power. Just bought a replacement harness plug from chevy and wired it in.

11-16-2020, 11:06 AM	#1
pound41 Registered User Join Date: Dec 2002 Location: Northern Virginia Posts: 1,268	2003 GMC 2500 HD 8.1L need help with cruise control wires Hello I have a 2003 GMC 2500HD 8.1L goes into reduced engine power PO2135. Everything has been swapped out with new GM still does it. I am getting a new harness made. I have to give the builder lengths for the wires. I cannot find the path for the cruise control wires to the column. are they 1 long wire or do they go into the ecm and another wires comes out? any help is greatly appreciated

11-16-2020, 11:38 AM	#2
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,118	Re: 2003 GMC 2500 HD 8.1L need help with cruise control wires The 8.1's in that year were wired like an LS engine, the cruise wires come out of the TAC module, there are three of them. THat said, throwing a harness at that problem is just throwing money at the problem. What all have you replaced? It sounds like its most likley the gas pedal/sensor. __________________ My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html 5.3 swap into my RUSTY '71 C10 http://ls1tech.com/forums/conversion...71-c-10-a.html

11-16-2020, 05:44 PM	#3
pound41 Registered User Join Date: Dec 2002 Location: Northern Virginia Posts: 1,268	Re: 2003 GMC 2500 HD 8.1L need help with cruise control wires Everything has been replaced with new GM. I bought the truck new. I had it a few weeks. one cold morning I started it up it drove fine went to the store to get morning coffee. Came out started it up the truck shook I read the Reduced Engine Power. turned it off restarted it and it started right back up. I called the dealer and told them what had happened. They said if it does it again bring it back in. Over the next 16 years it would occasionally do just that. In 2019 it started getting more frequent and taking more times to start. The connector and wire leads at the throttle body were replaced because TP1 had the 5 volt reference and TP2 was at 4.2. After that for the first time in 16 years in went into REP while I was driving it. Changed the throttle body good for a week then REP. TAC module good for a few weeks then REP. ECM good for a few weeks then REP. Pedal assembly was changed went into REP after about 15 minutes of running in my driveway. Took it to the dealer they replaced some pins at the TAC connector good for a few weeks then REP. I had thought the connector at the TAC module was the issue. So I swapped in a new one good for a few weeks then REP.

11-17-2020, 10:30 PM	#4
Hidesertchevy Senior Member Join Date: Mar 2017 Location: yucca valley Posts: 268	Re: 2003 GMC 2500 HD 8.1L need help with cruise control wires I had the same problem ended up being broken wire inside insulation at the intake throttle body harness plug. Same reduced engine power. Just bought a replacement harness plug from chevy and wired it in.



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