Issues with 2001 gmc sierra...any ideas?

[Bullshop Junior]

I have a 2001 GMC sierra 1500 5.3L 4x4 with the 4l60e in it. Today it started acting wierd. The speedo started bouncing. Just a little at first, but by the time I got home it was a constant bouncing back and fourth up to 20mph. It only does it in drive. If you shift down it works fine. Towards the very end of the drive it started randomly shifting and then everyonce in a while the rpm would just jump about 200. The whole time the parking brake light was randomly flashing. Not in a pattern. Just random. Where should I start looking to fix this? Wanna get it fixed before i mess something up....

[Ford SD]

I have a 2001 GMC sierra 1500 5.3L 4x4 with the 4l60e in it. Today it started acting wierd. The speedo started bouncing. Just a little at first, but by the time I got home it was a constant bouncing back and fourth up to 20mph. It only does it in drive. If you shift down it works fine. Towards the very end of the drive it started randomly shifting and then everyonce in a while the rpm would just jump about 200. The whole time the parking brake light was randomly flashing. Not in a pattern. Just random. Where should I start looking to fix this? Wanna get it fixed before i mess something up....

Not a GM fan Drive a Ford
Might not solve problem
How many coils Does it have (one per cylinder)

Have had problems rpm jump when have a bad coil

Water / corrosion have gotten in and corroded one of the terminals on the coil connections
Fixed it by using an old spark plug file (fine app 1/4w x 1/32 thick 6inch long) to file the corroded terminal --blow dirt out and reconnect wire

Just be carefull you don't brake anything

Might not be your problem?
Flash light and good vision and a bit of time and you can check connections

[SP5315]

Check the connector from the speed sensor wire harness at the transmission. This was my exact issue in my GMC Savana, caused speedo to jump around along with an intermittent ABS light.

[Mod42]

Check the alternator, doesn't sound like the problem but low output can make the inst cluster crazy, should be about 14 volts.
This is about the correct vintage for bad inst clusters, however the normal failure is the odometer goes out then the the speedo, or the gauges read incorrectly.
What I would look for in my shop would be a torque converter not locking up properly. Get the truck to a GOOD scan tool to see if the are tranny codes! from your description I fear transmission problems!

[smokeywolf]

Start by scanning for error codes.

[Bullshop Junior]

Check the alternator, doesn't sound like the problem but low output can make the inst cluster crazy, should be about 14 volts.
This is about the correct vintage for bad inst clusters, however the normal failure is the odometer goes out then the the speedo, or the gauges read incorrectly.
What I would look for in my shop would be a torque converter not locking up properly. Get the truck to a GOOD scan tool to see if the are tranny codes! from your description I fear transmission problems!

I was wondering about the tourqe converter but its puzzling it only does it with the shifter in drive. If you shift the shifter to 3 it stops. If you have it in drive and push the gas down to shift down it doesn't go away though...

[MTtimberline]

Sounds like the instrument cluster assembly is failing.

[freebullet]

I would check all grounds and both battery terminals for cleanliness. If you have to clean anything disconnect the - terminal fer a couple minutes before driving again. Then getter scanned if it persist.

Bad grounds
Tranny solenoids
Torque converter-not unlocking can cause surges at idle and an overly rich running condition. To the point your oil will smell like gas as it progresses.
Speedo cluster

Does it do anything strange at idle in drive?

[texassako]

Check the connector from the speed sensor wire harness at the transmission. This was my exact issue in my GMC Savana, caused speedo to jump around along with an intermittent ABS light.

I would definitely check this first, especially since it is in the transfer case you just replaced I think. Electrical gremlins can be a pain.

[geargnasher]

The small gauge, single ground wire that attaches to the back of the engine block, WAYYYYY back behind the plastic intake manifold and just above the tranny bellhousing where you can't see it without a mirror and flashlight, is broken inside the insulation right at the base of the crimp on the ring terminal. Remove the ground bolt, splice on about six inches of new wire and a new, 3/8" diameter ring terminal, clean the grounding area to bare metal, and reinstall the bolt and ground wire.

You're welcome.

Gear

[smokeywolf]

Good to know gear. I have a 2001 Yukon.

[Bullshop Junior]

Wasnt the problem gear. Just lost 3rd and forth on the way home from work

[Mod42]

Wasnt the problem gear. Just lost 3rd and forth on the way home from work

Get to a shop and have it scanned!! When you know what the codes are you can start to look in the right places, until then all of the free advice you are getting is worth exactly what you have paid for it!!

[Bullshop Junior]

Doesnt show any codes. I know what's wrong with it. Now just have to come up with the money for a tranny

[Fishman]

I have a 2000 model with the 5.3 and auto. I lost gear 1 and 4 and it was just a shift solenoid so you may not need a tranny. Pay no attention to the Ford loving Chevy basher, he's used to having to replace coils on each cylinder LOL :). I'm just shy of a quarter million miles on my z71 with only the aforementioned solenoid issue with the powertrain.

[Bullshop Junior]

Mine isn't a solenoid. Most of the time tht just causes it to not shift. This shifts into 3rd and then there is just nothing there. It's happened to several of te Chevys I have had, so nothing new. All the other ones just went clank and quit working, so the speedo thing threw me off.

[TXGunNut]

Sounds like the instrument cluster assembly is failing.


We have a winner!

[Bullshop Junior]

We have a winner!

I'm pretty sure not. The speedo sensor is on the input shaft. All other gauges work fine. Now that I have lost third and fourth the speedo does not work at all.

[tomme boy]

Didn't you just have a transfer case problem with this truck? Does the transfer case and trany share the same fluid? I thought some did?????

[Bullshop Junior]

This one does not.

[garym1a2]

I would look at the shift solenoids, I had that tranny in a Trailblazer, shop said I needed a new tranny. Second shop changed the solenoids. That was at 130K miles, than at 190K it started to do the same thing again, not wanting to shift. This time I brought two solenoids at $20 each and also a new filter. Dropped the pan and its a simple connector, than one screw to remove it. Once I did this the noticed the plunger was sticking, I pressed it a few times and it comes out with a lot of grey matter. Once I change both solenoids the truck ran fine. The kid now has 220K miles on it and its running fine.
Job was very simple as the hardest part was just dropping the pan.

[Lloyd Smale]

sounds like your computer took a ****. Its about the only thing that controls your dash, your shifting and your motor. Ive seen it a number of times with chevs where it didnt even flash a code because showing a code is also controled by the computer. Another guess is an intake manifold leak. they were known for them and the loss of vaccum will cause shifting problems, engine missing and because your brakes are vaccum operated may cause a brake alarm to come on.

[Bullshop Junior]

I'm starting to wonder about the tail piece sensor. That ujoint has went out twice, and with the build of ice on the driveshaft in canada it has taken quite a beating, and I'm wondering if it damaged the speed sensor. I have tomorrow off work I think so will probably start tearing into it more tomorrow. The tranny works fine for a few mins when the truck is cold usually, but as it warms up it will start failing

[freebullet]

Well if it were just plain wore out it probably wouldnt work at all. You may be on to something there. Sometimes these all electronic hunks make you miss the simplicity and poor milage of the late 70's iron pickups. Best of luck and keep us updated.

[Mk42gunner]

Well if it were just plain wore out it probably wouldnt work at all. You may be on to something there. Sometimes these all electronic hunks make you miss the simplicity and poor milage of the late 70's iron pickups. Best of luck and keep us updated.

Yeah but it would be hard to go back to 8-11 mpg for a daily driver, probably even worse with all the alcohol in the gas these days.

Robert

[Lloyd Smale]

thats what makes me think manifold leak. thats how they act when they leak. When there cold they seal and when the warm up and expand they start leaking. Very common problem with these motors.
I'm starting to wonder about the tail piece sensor. That ujoint has went out twice, and with the build of ice on the driveshaft in canada it has taken quite a beating, and I'm wondering if it damaged the speed sensor. I have tomorrow off work I think so will probably start tearing into it more tomorrow. The tranny works fine for a few mins when the truck is cold usually, but as it warms up it will start failing

[Lloyd Smale]

yup and wore out or rusted out by a 100k.
Yeah but it would be hard to go back to 8-11 mpg for a daily driver, probably even worse with all the alcohol in the gas these days.

Robert

[6bg6ga]

Don't bother with cheap part shop diagnostic units they are junk. Go to the GM shop and have them run diagnostics on it and you will be fixed and running within an hour.

[Bullshop Junior]

I got it figured out. The actual sensor is bad. Moot her up and running on all four gears last night. Thanks for the help guys!

[MtGun44]

"actual sensor"????

Is this the tailshaft you were talking about? Can't imagine why this wasn't
throwing a code.

Bill

[Bullshop Junior]

"actual sensor"????

Is this the tailshaft you were talking about? Can't imagine why this wasn't
throwing a code.

Bill

My phone is being stupid latly. Ill white up a post spelled the way I want it and it will change the spelling of some words. Sometimes I catch it. Sometimes not.

I was trying to say speedo sensor.

[Dark Helmet]

Good thing you didn't order that new/rebuilt/used trans, huh?:kidding:

[MtGun44]

OK, so a failed speedo sensor - makes the tranny think the car is going the wrong speed or no speed
and you get the wrong or no gear.

Handy. Still can't understand why the computer isn't smart enough to throw a code.
Seems like looking at the possible rates of change of speed and comparing to the
data on speed would show impossible acceleration or decelerations happening, so
a code should be set. Of course, this assumes good programming. . . . . . .

In any case - good that you found it. Probably a whole heck of a lot less than a tranny. :-)

Bill

[6bg6ga]

OK, so a failed speedo sensor - makes the tranny think the car is going the wrong speed or no speed
and you get the wrong or no gear.

Handy. Still can't understand why the computer isn't smart enough to throw a code.
Seems like looking at the possible rates of change of speed and comparing to the
data on speed would show impossible acceleration or decelerations happening, so
a code should be set. Of course, this assumes good programming. . . . . . .

In any case - good that you found it. Probably a whole heck of a lot less than a tranny. :-)

Bill

I will agree.

[Bullshop Junior]

It actually didn't cost me a thing to fix. There are two sensors on the tail piece. One for the speedo and one for the auto 4wd. Same sensor, just right across the tail piece from eachother. So I just swapped the wired around and she is working just fine for now.

[6bg6ga]

So now you have no speedo?

[TXGunNut]

So now you have no speedo?

No, speedo will work and tranny will shift properly but the computer that runs the auto 4X4 will be a bit confused.

[TXGunNut]

I'm pretty sure not. The speedo sensor is on the input shaft. All other gauges work fine. Now that I have lost third and fourth the speedo does not work at all.

Good. Common problem, expensive fix. The speedo sensor is on the output shaft or transfer case, in your case I believe it's on the xfer case. Tranny has at least one speed sensor on it, some also have turbine speed sensors. Glad you got things working again.

[Lloyd Smale]

glad it figured out cheap.