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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1667
Experience:  GM Grand Master Technician 2007. 14 year experience.
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1994 GMC SIERRA 3500 DUALLYWITH 454 ENGINE, OD AUTOMATIC

Customer Question

1994 GMC SIERRA 3500 DUALLY*****WITH 454 ENGINE, OD AUTOMATIC TRANS.
Going down the highway at highway speeds, kicks out of gear, revs the engine, nothing happens, pull the shifter into drive nothing happens, pull the shifter into 2nd and then you have your transmission back, but high RPMs. I have to stop the truck and disconnect the battery, then start all over. Sometimes it does it a lot, other times it doesn't even happen.
Submitted: 5 months ago.
Category: GMC
Expert:  Reggie Whiddon replied 5 months ago.

Hello the fact that this is an intermittent problem and you can get it to reset leads me to beleive it may be an electical issue, on your transmission if it lost all power down to the trans its default position is second gear regardless of where the shifter is. I have had several do what you are describing and the most common issue was beleive it or not ignition switch, Get you a voltmeter check the voltage on both sides of the trans fuse, you want it to be near battery voltage and if you have tilt wheel jar the wheel up and down turn it and you may see voltage drop if it gets below 9 or so volts the solenoids lose power and bam your in second

Customer: replied 5 months ago.
No, I have to manually put it into second to get any kind of power back to the rear wheels. It does not go there on it's own. It is like it is put into neutral.
Expert:  Reggie Whiddon replied 5 months ago.

i understand, and do you have the 4l80e? If so I would still check the voltage at the fuse please trust me it will eliminate that as a possibility and it is very common. Have you scanned for any codes in the computer

Customer: replied 5 months ago.
I am not sure what trans it is. How do I check. I was told when I bought the truck used (and here I exposed my ignorance) that it had an "underdrive" also. Is that even possible. I have had this truck since 2000. About 10 years ago, I had it worked on and was told this problem was the "speed sensors". They said they fixed it, but I have been having trouble with it for quite some time now and it is getting worse.
Expert:  Reggie Whiddon replied 5 months ago.

Good morning, no i dont know of an underdrive. Your truck most likely has the 4L80E couple of ways you can find out one the pan on the trans is it square? If so it would be a 4L60E which i doubt if not it would be the 80 those were the only two automatics used.

The speed sensors are another frequent problem but usually will drop u to second if they fail, and you are reporting no pulling at all. Do you have a code reader to scan for codes

Customer: replied 5 months ago.
Reggie, sorry I work weird shifts and odd hours. Anyhow, I thought the "underdrive" thing was strange, I had never heard of one. I will be unable to look at my pickup until Saturday. I will find out what trans I have. I have my hands on a code reader so I will try that also. I will check it first thing, then I will drive it and hope to recreate the problem (which shouldn't be a problem) and report those findings back to you for more assistance.
Yea, you understand correctly, it does not drop into second. I have to manually do that. Otherwise I have just coasted to a stop with no pull whatsoever in OD or Drive. It does not have a tilt steering wheel. Great truck, just want it to be reliable.
Expert:  Reggie Whiddon replied 5 months ago.

sir we are perfect for each other i to work strange hours I will be looking for your reply thanks

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