4X4 problems - yeah I've seen the other posts

JimmyGold · 07-20-2006, 06:03 PM

Ok guys here's the deal,

Last week I had a used ATC put in my 2K Jimmy to the tune of $600. The truck was engaging 4 wheel drive on its own. When last I had this problem two years ago I plugged in a new TCCM I got from GM Partsdirect and it worked.

After the guy did the diagnostic last week he assured me that it wasn't the TCCM but the differential on the ATC. He also said it was cheaper just to get a used ATC from the junkyard. This just didn't make sense to me because the problem seemed more electrical (module or switch related)than mechanical because the the 4WD was actually engaging...but I went ahead and followed his advice.

Today, the 4WD started going crazy again engaging 4LO at its own discretion. By shifting into neutral and playing with 4WD selector switch in the dash I got the car in 2WD, once I did that I just took the ATC fuse out to keep it from engaging again.

1 - Who should I curse out, I really want my money back because apparently my old ATC was fine.

2 - What is the next logical place to check. I've seen a variety things mentioned in previous posts (Actuator Switch, Vacuum Lines, Encoder Motor). Some clarification would help so I can articulate it properly.

3- Why would it start acting up again after a 10 days of smooth sailing?

Thanks so much!

MT-2500 · 07-20-2006, 09:09 PM

Quote:

Originally Posted by JimmyGold

Ok guys here's the deal,

Last week I had a used ATC put in my 2K Jimmy to the tune of $600. The truck was engaging 4 wheel drive on its own. When last I had this problem two years ago I plugged in a new TCCM I got from GM Partsdirect and it worked.

After the guy did the diagnostic last week he assured me that it wasn't the TCCM but the differential on the ATC. He also said it was cheaper just to get a used ATC from the junkyard. This just didn't make sense to me because the problem seemed more electrical (module or switch related)than mechanical because the the 4WD was actually engaging...but I went ahead and followed his advice.

Today, the 4WD started going crazy again engaging 4LO at its own discretion. By shifting into neutral and playing with 4WD selector switch in the dash I got the car in 2WD, once I did that I just took the ATC fuse out to keep it from engaging again.

1 - Who should I curse out, I really want my money back because apparently my old ATC was fine.

2 - What is the next logical place to check. I've seen a variety things mentioned in previous posts (Actuator Switch, Vacuum Lines, Encoder Motor). Some clarification would help so I can articulate it properly.

3- Why would it start acting up again after a 10 days of smooth sailing?

Thanks so much!

Proper testing.
On that one a good trans/transfer case scanner should point you to the problem.
Any transfer case codes?
MT

rlith · 07-21-2006, 08:21 AM

1st Check vac actuator under battery tray for tears, or leaks, and that the vac hose is connected. Replace if found

2nd Check vac hose leading from vac actuator to vac switch on transfer case for cracks and dry rot. Replace if found.

3rd Check remaining 2 hoses from vac switch on transfer case for dryrot or cracks Replace if found.

If all of the above are fine, disconnect your negative battery cable for 1/2 hour then reconnect it. If your 4x4 works after that you probably have a failing TCCM (Transfer case control module)

If that doesn't solve it, it's most likely the encoder motor

jhong1226 · 07-21-2006, 10:37 AM

Something is shorting out in your wire from the switch to your shift motor, when it shorts out it tells your shift motor to switch drive.
Try checking those wires first.

JimmyGold · 07-21-2006, 10:57 AM

For some reason I'm not seeing my reply...anyway thanks so much. I'm headed to the mechanic now.

Since I've actually replaced the entire ATC, shouldn't the encoder motor be eliminated as an issue? It should either be a switch or the TCCM, right?

Thanks again!

JimmyGold · 07-21-2006, 02:36 PM

Ok, the trouble code I have is U1000. I'm googling now...any help would be appreciated. Thanks!

MT-2500 · 07-21-2006, 03:20 PM

Quote:

Originally Posted by JimmyGold

Ok, the trouble code I have is U1000. I'm googling now...any help would be appreciated. Thanks!

What kind of scanner are you using.
Any fuses blowed?
http://www.troublecodes.net/OBD2/Ucodes.shtml

rlith · 07-21-2006, 03:26 PM

U1000 and U1255 Class 2 Communication Malfunction/Loss of Communication Undetermined

Most likely your power wire at the ALDL is bad or the serial wire is bad.

JimmyGold · 07-21-2006, 04:11 PM

Aldl?

rlith · 07-21-2006, 04:35 PM

Quote:

Originally Posted by JimmyGold

Aldl?

The port you hook up a scanner to. It's called the ALDL. It stands for Assembly Line Data Link or Assembly Line Diagnostic Link. Either term is acceptable

LS19962DRBLAZER4X4 · 07-21-2006, 07:48 PM

Don't take it to Mr Goodwrench .... He will drop it on his foot...

JimmyGold · 07-22-2006, 12:52 AM

lol...just for clarity the trouble code (u1000) is what caused the mechanic to conclude that I needed a new transfer case (I know I got ripped). That was ten days ago, then yesterday the selector on the dash started going crazy again causing 4wd to engage. So today I took it back, raised cane, and this time there were no codes, although the symptoms were the same. At my suggestion (thanks to you guys) they checked the vac hoses and switch, and eventually changed the switch on the ATC.

Left the garage and within a half mile, the selector went crazy again. I was too tired to go back. In the meantime I took out the ATC fuse in the relay box under hood, for a few hours. When I plugged the fuse back in the "service 4wd" lit up for about 10 sec then all of the selector lights lit up and then only the 2wd light stayed on and the service light went out- as if it was reseting itself. It stayed that way for a good 60secs, then I shut the engine off. I doubt this solved my problem, but we'll see tomorrow.

Thanks for everything guys!

JimmyGold · 07-22-2006, 11:30 AM

Now I'm 99% sure that it's the TCCM.

MT-2500 · 07-22-2006, 12:54 PM

Quote:

Originally Posted by JimmyGold

Now I'm 99% sure that it's the TCCM.

Remember you have already throwed 600$ at it.
Throwing more parts at it may help and may not.

You need to get that communications network working and get in there with a scanner and find out what is going on.
MT

JimmyGold · 07-22-2006, 08:57 PM

yeah, but we're not getting any codes...the U1000 was stored from the previous week. Also, this is exactly what happened three years ago, wound up being the TCCM.

My truck has been an electrical nightmare. I've gone through 4 batteries, 3 alternators, radio is half lit, driver's seat and rear wiper done, signal switch replaced and I've already gone through on TCCM.

thanks again guys!!

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