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1999 GMC Jimmy won't shift from 4wd to 2wd, hear loud clicks when shift from 4w high to 4w low and visa versa, nothing when try to shift into 2wd, also, want to check tranfer case oil but do not know what kind to replace it with if low all manual says is gm part # 12378396
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On the transfer case Transfer Case - Electronic Shift
The four-wheel drive electronic shift-on-the-fly feature electrically shifts the vehicle transfer case between 2WD, 4WD HIGH, and 4WD LOW. The system mode is selected by the operator through the mode select switch (MSS) on the instrument panel. The operator is informed which mode the system is in by two instrument cluster indicators: one for 4WD HIGH which appears as 4WD, and one for 4WD LOW, which appears as 4WD LOW. Shifts into 4WD HIGH can be made at any speed. When shifting into 4WD HIGH with the vehicle stationary, tooth blockage may occur preventing shift completion. When the vehicle is driven above 8 km/h (5 mph) the shift will complete. When shifting in or out of 4WD LOW, the four-wheel drive (4WD) control module requires that the vehicle speed be less than 5 km/h (3 mph), the brake pedal be applied, and the transmission be in NEUTRAL (automatic transmission) or the clutch pedal be depressed (manual transmission).
The gearmotor encoder assembly is mounted externally on the transfer case. It drives a rotary cam which moves the mode fork and range fork within the transfer case between the 4WD HIGH, 4WD LOW, and 2WD range positions.
The four-wheel drive (4WD) control module controls the gearmotor encoder assembly that shifts between 4WD HIGH, 4WD LOW, and 2WD modes.
Yes i can, your engine may slip a bearing causing you to loose your engine. The other thing also is that the oil can not cool down your transfer case fast enough causing the bearing inside the transfer case to fail.
Try to gate your 4WD repaired soon if it's tuck in 4wd low. Keep me posted if that is the case and be happy to help you get your Blazer running 100% again soon.
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sounds like it might be an encoder moter, but the best thing you can do is take it to a good transmission shop so they can hook up their reader and find out for sure
The transfer case is stuck in the low range. If manual shift try shifting from low to high several times to see if free up. If electronic, check all fuses and make sure you hear transfer case change range. Do this by shifting with key on engine off. If no change refer to qualified transmission mechanic.
Hi:
The main parts to the 4WD system are the transfer case, the shift control motor, and the shift control module. if you remove the shift control motor from the transfer case, and leave it plugged into the harness, you should be able to see if it functions thru all settings, such as 4wd high or low or 2wd. If not, then you need to figure out which part is bad, the motor or the control module. If it does work as it should, then you have some sort of transfer case problem.
Usually when a truck gets stuck in 4 low you need to put it in reverse, start backing up very slowly, put it in neutral (or push in the clutch on manual trans models) and stop the truck with the brakes. this will release the load on the gearing which should allow you to shift out of 4 low.
sounds like the vacuum lines are either pinched or the vacuum pump is shot. try getting a mechanic look at the lines on and around your transfer case... also try checking the fuses for the 4wd selector. let me know how it goes
sounds like it is loosing vacuum check all the lines for a crack even the engine lines will cause it to loose vacc. pressure. if it is not run to the vacuum reserve canister you may not have enough vacc. to hold the actuator in several times I just run new lines and that helped and not very costly.
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