2003 GMC Sierra problems! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Mudslut07 · 03-01-2012, 11:39 AM

My biddy has a 2003 GMC Sierra SLE 4x4 5.3l. The truck stared as stock but he decided to jack it up and start messing with mods,long story short,a nice truck went to a mud beater real fast and things went downhill from there. The tranny he has in it now was rebuilt maybe 6,000 miles ago and had a shift kit put in. He also installed a tb spacer and a superchips programmer. The truck ran awesome for awhile but then the service brake system light started going crazy and he lost 3rd and overdrive. He went to a local junkyard and got a whole new wiring harness from the cpu to the trans/transfer case and put it on,he claimed this fixed it for a few days. Now he is thinking it's his tps sensor? Anyone have any input at all?

Thanks in advance

clinebarger · 03-01-2012, 08:45 PM

Have it scanned, Post the codes.

If the trans has a electrical failure the shift solenoids are turned off and the only forward gear will be 3rd.

When he Loses 3rd & 4th does it slip/neutral feeling?

Stop throwing parts at it!

CAGRacing · 03-04-2012, 02:52 AM

Never shift kit and programmer shift kit together. Just an fyi. I've been told it leads to near instant valve body failure.
Drop the pan and check for shavings and replace fluid. May be simple fix, may need another tranny.
As far as brake light being on, welcome to wheeling. Those fragile sensors like to occupy the same space mud does and one easy trail run can force shtf

03-01-2012, 11:39 AM	#1
Mudslut07 Registered User Join Date: Dec 2011 Location: Eastlake,mi Posts: 18	2003 GMC Sierra problems! My biddy has a 2003 GMC Sierra SLE 4x4 5.3l. The truck stared as stock but he decided to jack it up and start messing with mods,long story short,a nice truck went to a mud beater real fast and things went downhill from there. The tranny he has in it now was rebuilt maybe 6,000 miles ago and had a shift kit put in. He also installed a tb spacer and a superchips programmer. The truck ran awesome for awhile but then the service brake system light started going crazy and he lost 3rd and overdrive. He went to a local junkyard and got a whole new wiring harness from the cpu to the trans/transfer case and put it on,he claimed this fixed it for a few days. Now he is thinking it's his tps sensor? Anyone have any input at all? Thanks in advance Attached Images __________________ 1992 Chevy K1500- 6in ProComp lift 2001 Yamaha Yz426f 1999 Ski-Doo MXZ 600-all the goodies Run your truck...Not your mouth!

03-01-2012, 08:45 PM	#2
clinebarger Senior Member Join Date: May 2009 Location: Fort Worth, TX Posts: 6,370	Re: 2003 GMC Sierra problems! Have it scanned, Post the codes. If the trans has a electrical failure the shift solenoids are turned off and the only forward gear will be 3rd. When he Loses 3rd & 4th does it slip/neutral feeling? Stop throwing parts at it!

03-04-2012, 02:52 AM	#3
CAGRacing Registered User Join Date: Oct 2010 Location: Kansas City MO Posts: 33	Re: 2003 GMC Sierra problems! Never shift kit and programmer shift kit together. Just an fyi. I've been told it leads to near instant valve body failure. Drop the pan and check for shavings and replace fluid. May be simple fix, may need another tranny. As far as brake light being on, welcome to wheeling. Those fragile sensors like to occupy the same space mud does and one easy trail run can force shtf



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