Question about 2003 GMC Sierra 1500

1 Answer

GMC Sierra 1500 power loss at 1/2 throttle and above

Last week the pressure fitting on the heater core failed. traffic. It emptied the cooling system completely, and I had to drive about a half mile before traffic would allow me to merge to pull over in a shopping center to diagnose what happened. during this half mile drive, the temperature rose to over 260* indicated, and the engine went into a protect mode/power reduction. I was able to clamp the failed circuit of the the cooling sys. to get to the dealer and get the part, but once changed, and fixed, it will run fine, and then reduce power. anything above 1/2 throttle and you can feel it lose power- let the gas off real slow, and you will actually accelerate a bit. I also noted the tem will rise and fall abruptly on my gauge, so this is a kind of "red flag" to me.. I also replaced the thermostat today thinking the excessive heat may have affected the temp. range of the existing thermostat. reset the ecu, (left the batt disconnected while I changed the thermostat) And now the service engine light is off, but the power reduction is still evident at above 1/2 throttle position. I thought it might be the tps, but what are the odds that it would go out at the same time as the coolant fitting bursting?

Posted by exciter900rr on

  • exciter900rr Oct 27, 2008

    actually, believe it or not, my knock sensor was the culprit-  all that steam and water shooting over the intake.....  yup filled the knock galleys and poof! p033 or whatever the code is....   about $150 later in sensors and gaskets, and fixed.



1 Answer


  • Level 1:

    An expert who has achieved level 1.


    An expert who has answered 20 questions.


    An expert that has over 10 points.


    An expert whose answer got voted for 2 times.

  • Contributor
  • 29 Answers

I had this problem when the engine goes into protect mode you will have to reset with a scanner and reset the fuel air mixture cause it dont reset it self i hate these computer model car

Posted on Oct 27, 2008


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Instruments not working on 1997 Jimmy, after replaceing the heater core

Check, you may have a connection to the cluster not fully plugged in. It's got to be at the cluster-the instrument panel.

Dec 24, 2013 | 2004 GMC Sierra 2500

1 Answer

2000 GMC Sierra radiator cap location

park it on an uphill slant take rad cap off and let it burp the air out.

Nov 25, 2017 | 2000 GMC New Sierra 1500

2 Answers

I have a 1997 GMC 5.7 4x4 extendacab 3 door 1500. i am not getting heat. i changed the heater core and the thermostat. i checked the oil to see if i had antifreeze ana water in it but there is none in the...

Have you checked for vacuum leaks? Some vehicles from that era used vacuum pressure to control heating/cooling baffles. If you have a bad vacuum leak, then the baffle will never swap over from vent/cooling to heating.

Sep 16, 2010 | 1993 GMC Sierra K1500

1 Answer

Hi...2008 gmc sierra crew...check engine light came on thought maybe was standard just before hitting 30,000 then noticed low oil pressure ( 20 ) then noticed clacking noise?

Sounds like an oil pressure problem. The clacking sound is most likely the lifters are collapsing due to loss of oil pressure. You may have a failing oil pump.

May 08, 2010 | 2008 GMC Sierra 1500

2 Answers

Flushing the heater core

I removed the hoses and took a air nozzle at low pressure and blew in the return hose connection of the core. A big chunk of paste like substance shot out then pure liquid. I put the hoses back on and tested it. Now its blowing hot!!!!!!!

Apr 10, 2010 | 2000 GMC Sierra

2 Answers

I have 93 gmc 1500 truck with throttle bodey

Check your fuel regulator and replace the injectors.

Mar 23, 2010 | 1995 GMC Sierra C1500

2 Answers

2005 GMC Sierra 1500 - heater blows, but only cold air

Check coolant level. Check for heat at the heater hose going from water pump to heater core at firewall. Check to see that cable is moving coolant control valve from the closed to open position. Low mileage so it shouldn't be plugged heater core.

Jan 07, 2010 | 2005 GMC Sierra

1 Answer


Try “” or your local library for diagrams and step by step instructions and for GM parts try Schram auto and truck parts 1-800-292-1032

Mar 07, 2009 | 1996 GMC Sierra

1 Answer


Your heating system is run by your cooling system. If your cooliant is low then you are not going to get adiquiate heat disapation to your heater core. So check the entire cooling systerm. Your water pump (low flow), hoses (leakage), you already checked the thermostat & heater core. So other than that I don't know.

Jan 15, 2009 | 1999 Chevrolet Silverado 1500

2 Answers

Loss of power

The problem could be a plugged cat convertor, or fuel filter

Dec 21, 2008 | 2003 GMC Sierra 1500

Not finding what you are looking for?
Cars & Trucks Logo

396 people viewed this question

Ask a Question

Usually answered in minutes!

Top GMC Experts


Level 3 Expert

85239 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22485 Answers

Jeffrey Turcotte
Jeffrey Turcotte

Level 3 Expert

8984 Answers

Are you a GMC Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides