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Need help determining if problem is bad throttle position sensor (TPS) or transmission

dukbludvl
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dukbludvl Enthusiast

dukbludvl

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Posted

Hello - I need your help.  My 2005 Yukon 2wd 5.3L gas motor (not flex fuel) with 290k miles just started giving me problems.  I can't figure out if it's merely a bad throttle position sensor (TPS) or if the transmission is going.  Here are the symptoms:

 

1. For the last month or so, I've noticed that while I'm breaking it seems like the vehicle is simultaneously getting gas because it lurches forward a bit like it's trying to accelerate.  Now, this could be because my size 15 foot someone tapped the gas pedal while I was breaking, but I'm not 100% sure.

2. I've seen fuel economy dip from 17mpg to low 15s.  Some of this could be just variations in driving patterns, I'm not sure.

3. The main thing is that a few days ago I accelerated hard from a stop, and when I did that the vehicle really took off like it never had before almost -- threw my head back a little even.  After that incident, I noticed that it no longer shifted right.  It'll start out in first and the tach will go up to 2,000 or 2,500, and the only way to get it to shift to second is to let off the gas for a few seconds, and the tach will come down and it'll shift.  I don't think it's shifting up to 3rd at all, and there definitely doesn't seem to be any overdrive.  I can get it up to speeds of 55-60, presumably still in 2nd (?) with the tach up around 2500rpms at those speeds.  Can't seem to get it any higher.


Question is -- is this a bad TPS or is my transmission shot?  Initially, I thought probably transmission, but then I started reading about the TPS and related symptoms, and it sounds like it could be that.

 

Also, if anyone has any info on steps to change the TPS, please let me know.  Manual pages or whatever.  I believe the TPS I want to change (if it's even that) is on the left side of the throttle body, right?  I know there's another sensor on the actual accelerator pedal itself, but that's no the one I need to deal with, right?

 

Thanks in advance for any help.

 

Brian715 Enthusiast

Brian715

Posted
Posted

If it's the original 290k mile 4l60 it's the trans. If it's the second trans but it was replaced more than 150,000 miles ago, then it's the trans. But a tps is only like $30 so if you think it might be that, grab one and see if it fixes it. Never had a tps issue on my 290,000 mile 99 NBS, my 250,00 mile 02 5.3l suburban, or my 06 306,000 mile 1500 5.3l. But they all needed at least one trans. Hope you can get it sorted. Also, Any decent obd2 scanner should be able to monitor the tps in real time and see if it's giving the correct signal. 

Ian Mills Enthusiast

Ian Mills

Posted
Posted (edited)

I'm leaning towards transmission too (but a TPS is cheap like Brian said). 2500 seems low for 2nd at 55 to me. I wonder if your truck is actually shifting into 3rd when you let off the gas. What's your tire height and rear end ratio?

I'm heading this direction because it sounds exactly like an issue I had with an old 700R4 where the 2-4 band went out. (And, as you may know, the 4L60e is kindof just a rebranded 700R4)

What happens if you are in low rpm in your higher gear and you floor the pedal? Does it try to downshift but only find neutral?

Edited by Ian Mills
Adding additional request for info
  • 3 weeks later...
dukbludvl Enthusiast

dukbludvl

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It is the original trans.  My tires are 265/70 R17.  I believe the rear end is 3.42.  If i'm at low rpm in the higher gear and I floor it, the rpms jump way up but I don't get the acceleration I'd expect.  Based on this, do you still think it's the trans?

 

I guess I could try to replace the TPS and see if that does the trick.  A new one is $98 at AutoZone.  Do I need to do some sort of idle relearn procedure or otherwise calibrate the new TPS?

dukbludvl Enthusiast

dukbludvl

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  • Author
Posted

Yesterday I got a CEL, and the code was for Shift Solenoid A stuck on.  Do you think I could just have a bad solenoid, or is this more likely a symptom of a larger issue?

  • 2 weeks later...
sefiroxx Enthusiast

sefiroxx

Posted
Posted

Solenoid on could be causing more problems (2nd band stuck on). Get it checked.

Surprised that CEL for the solonoid was not thrown earlier. You mIght ha vs burned up some clutches and the material is caught up in the system.

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