I have a 86 gmc s -15 and I need to shift it from 2 low to 2 high - it would save gas I believe, how do I do this correctly?

you can check the transmission fluid if its ok and also the transmission pressure

There are a few potential issues that could be causing your 2004 GMC Envoy SLT to go into 4-low but not 4-high or 2-wheel drive. Some possible causes include:

1. Transfer case issues: The transfer case is responsible for controlling the engagement of the different drive modes. If the transfer case is damaged or malfunctioning, it may not be able to engage 4-high or 2-wheel drive.
2. Shift motor issues: The shift motor is responsible for controlling the engagement of the transfer case. If the shift motor is damaged or malfunctioning, it may not be able to engage 4-high or 2-wheel drive.
3. Vacuum issues: The vacuum system is responsible for controlling the engagement of the transfer case. If there is a problem with the vacuum system, it may not be able to engage 4-high or 2-wheel drive.
4. Wiring issues: The wiring that controls the transfer case and shift motor can become damaged or corroded over time. This can cause the transfer case to not engage 4-high or 2-wheel drive.
5. Control module issues: The control module that controls the transfer case and shift motor can fail. This can cause the transfer case to not engage 4-high or 2-wheel drive.

It's best to diagnose the issue by a professional mechanic, who can perform a proper diagnosis and repair the issue. They will be able to determine the specific cause of the problem and recommend the appropriate repairs.

1994 GMC 4l60e transmission shifting problems - CarGurus

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CarGurusJan 17, 2011 - 1994 GMC 4l60e transmission shifting problems - I've got a 1994 GMC Sierra 4X4 5.7 I ... If you put it in low and lift the handle, it will go into second .... Justchange 1-2 - 3-4 solenoids first and if that doesn't work change the ...

Troubleshoot automatic transmission problems

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Jul 15, 2015 - Rescan the PCM for trouble codes, if none appear the problem could ...Excessively low transmission fluid (Note: If transmission is operated for an .... it waslow, and now my car will only shift from 1st to 2nd manually and will ...

I would recommend checking the fluid level and scanning your Powertrain Control Module (PCM) for fault codes. The syptoms you are describing can be caused by low fluid, low fluid pressure, worn-out clutches, malfunctioning shift control solenoids, or even a defective ignition switch not supplying the correct voltage to the transmission. Retrieving fault codes can help you tremendously in knowing which system is causing your problem and start you into the correct troubleshooting sequence.

I believe the FIRST and EASIEST thing that should be checked is the transmission fluid level. If it is low, you need to find out where it is leaking from.

Check your transmission fluid, if it is low, the transmission cannot shift into the correct gear from lack of hydraulic pressure. Be sure to check it while the truck is running.

If it is full, you may need to change the fluid and filter; over time the fluid will break down and trash the filter leading to low pressure problems which is why your truck fails to shift any more than 2nd.

Another problem may be that the torque converter is failing to lock yet again from lack of hydraulic pressure or its just worn out.

well, if you are sitting still it is recommended you put vehicle in neutral and select 4x4 indicator to desired posistion..... 4 high...4 low...or 2high (auto) when you select 4 low the top speed is not to exceed 25 mph. It is a very low gear for crawling or pulling. At any time you need 4 low gear you must stop trk, shift to neutral and select 4 low. The same procedure is done to change from 4 low to 4 hi or 2 hi. if not done this way internal trans, transfer case or driveline failure will occure. At any time you may shift 4x4 selector from (auto) or 2 hi to 4 hi, and 4 hi to 2 hi or( auto).****** But note, do not make shifts while tires are spinning or under power (acceleration)******* While driving you can make shifts at any speed between 2 hi (auto) and 4 hi and back to 2 hi. release throttle a little and select. you do not have to take foot off throttle all the way! just enough that truck is not under a power, load acceleration. If tires are spinning or you are on the gas and you select gears from 2 & 4 high the posibilities of severe damage can result. Also note that 4x4 is not recommended on dry pavement. When 4x4 is being used also take care as to the handling and the steering characteristics change, On tight turns the front wheels will bind and possibly **** a little. If you have never had a 4x4 before, obey what i have told you untill you get the experiance and you will be fine. HAPPY TRAILS.... AND A LITTLE 4X4 FUN!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The shift down linkage on the carburetor below the gas pedal cable might need to be adjusted to increase the hydraulic pressure on the internal clutch plates in the transmission it shows you how to do that in a car manual.

cHECK THE FUEL PRESSURE AT THE RAIL. iF LOW i WOULD CHECK THE INLINE FILTER AND THEN A POSSIBLE PUMP

I had a very similar problem with my 98 gmc 2500. The 4 low would engage - though the upshifts were erratic, but no 4 high though the light sometimes came on. I changed out the electric shift solenoid or whatever it is called, on the transfer case and it worked fine after that. A fairly simple fix that can be done in 15 minutes. Hope this helps.

Check the vacuum line that attaches to the front of the intake manifold to the transmission,( no cracks, splits, deteriated ends) sounds like vacuum is low