SOURCE: 4 wheel drive on 1999 chevy blazer
99 chev blazer should have an electric motor not a vac switch...Is your controll on the dash a switch you turn.. or on the floor you shift ??
SOURCE: 2000 s10 blazer 4x4
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/* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;}Hi: If the front diffis fine then it boils down to usually one of three things why it won’tengage. 1 – No power, 2 – relay notworking (located by passenger side) right side or 3 – no vacuum. The 1995 and up Jimmy’s and Blazer’s use thesame system for engaging the front diff. They are all made to “shift on the fly” while driving down the road withnothing to do but press the button on the dash. (Do NOT shift into 4 Low while driving at higher speeds at it can dodamage). If the dash light flashes andyou hear a clicking sound that means you have power to the relay. If the vehicle 4 High lights stops flashingand it goes back into 2 High then the problem is likely that you have no vacuumto the 4 X 4 actuator module which is located below the battery tray. Remove the battery and tray; look for a holeburnt in the vacuum line or actuator module rubber diaphragm. When the activator get vacuum it pulls acable that attaches to the front diff engaging it, when engaged the wires onthe front diff send a signal to the 4 X 4 light on the dash telling you it is engaged). If the battery has ever leaked the acid runsdown onto the actuator causing the problem. If no holes found in the hose or actuator diaphragm I would use batterycables and hook up the battery and start vehicle then check for vacuum byputting my finger on the end of the actuator hose. If there is vacuum then problem in actuatoror cable linkage. If no vacuum I wouldthen trace back the vacuum lines to find where it is off or leaking, NOTE: As the heater control operates on vacuum and some other vehicle systemsdo as well bear this in mind, has your vehicle had heater control problems orbeen running rough, this could explain a lot of potential problems. Attached to the hood on the left side(drivers side) on 1997 and older models is a vacuum (a “ball”) canister, newermodels the canister is located in the left fender by the brake module, makesure the vacuum line is attached there. Please rate this suggestion as I never know if it is worth my timefilling these things out…
SOURCE: My 1996 S-10 Blazer will not shift sometimes and
A faulty VSS (Vehicle Speed Sensor) or related wiring can cause both of your problems, trans and ABS. If the computer doesn't know the vehicle is moving, then it won't shift the trans. If the ABS controller sees wheel speed, but not vehicle speed, it will turn on the ABS light. The VSS is located in the rear transfer case housing. But remember, it may be the VSS, related wiring, a faulty speedo buffer (usually located in the dashboard), ECM, or even the reluctor on the transfer case output shaft. You may want to have a shop scan "data stream", or even have them diagnose the problem.
SOURCE: transfer case clunk 2000 chevy silverado 1500 4x4
One thing to check, which is often the culprit in these situations is the U-joints. With the truck off, crawl under the vehicle and grab hold of the shaft leading into as well as the shaft going out of your transfer case, If htere is a lot of "slop in it, chance are it is in need of repair. Also I would check the oil level in the transfer case, in an attempt not to challenge you intelligence, there should be a plug located in the lower part about 2 inches from the bottom or so. it usually has a square hole that a 1/2" ratchet fits into. Pull the plug, and stick your pinky into the hole, you should be able to feel the lubricant just below the hole, if not it is in dire need of a filling. also check for metallic remnants in the fluid. this is a sign that things are not as they should be. In that case contact a repairman for a more thorough look.
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I'm pretty sure that is a combination of the transmission output and the engine inputs (rpms, etc.) to the TRANMISSION CONTROL MODULE...
Best if you repost this question... JAMESSIZER is a constant SPAMMER and has sidelined your question from our VERY EXCELLENT FREE VOLUNTEERS.
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