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Old August 24th, 2011, 09:38 AM   #1
cornrowcornilius
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Default 1999 Blazer NV236 4X4 not working

I am at a fukcing loss here, friends 1999 ZR2 with a NV236 has NOTHING working on the 4x4. The lights on the switch flash briefly when the truck is started...but thats it. No switching on the vacuum switch, no engaging of the front axle, no click from the tccm. The dash switch has been replaced, fuses checked, pins on the TCCM cleaned. Any ideas of what to check next?
FAWKIN GM POS!
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Old August 24th, 2011, 12:19 PM   #2
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Check encoder motor, common problem.
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Old August 24th, 2011, 04:25 PM   #3
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Were the terminals corroded on the harness & the tccm ? The corrosion could have worked into the module. I assume that since you knew about cleaning them you know how common it is for the module to go bad. I'd try a new tccm, or a known good one.
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Old August 25th, 2011, 09:21 AM   #4
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Were the terminals corroded on the harness & the tccm ? The corrosion could have worked into the module. I assume that since you knew about cleaning them you know how common it is for the module to go bad. I'd try a new tccm, or a known good one.
No corrosion. Last night I disconnected the battery and touched the cables together per direction from another site. Now the it seems as if it is stuck in 4HI, the light on the switch flashes. If I push any of the buttons that button will flash a half dozen or so times then go back to 4HI. I can hear the axle actuator when I push the button...but that seems like the only thing that is happening. So does this sound like tccm, encoder, or actuator?
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Old August 25th, 2011, 12:10 PM   #5
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No corrosion. Last night I disconnected the battery and touched the cables together per direction from another site. Now the it seems as if it is stuck in 4HI, the light on the switch flashes. If I push any of the buttons that button will flash a half dozen or so times then go back to 4HI. I can hear the axle actuator when I push the button...but that seems like the only thing that is happening. So does this sound like tccm, encoder, or actuator?
If you can hear the encoder motor working and get flashing lights I would check the actuator, I do believe on a 1999 it has a sensor that detects when the actuator is pulled in when trying to engage 4x4, when the signal from that sensor is made you will get a steady light on the 4x4 switch, if it is not made but the encoder has engaged then the light will flash letting you know you have a problem.

The whole system is pretty simple, If you can hear the encoder motor working check that off the list, you replaced the switch so check that off the list. Now move on to the actuator, pull the vacuum hose going to the actuator and have someone shift it into 4x4 and see if it is pulling vacuum at the end of the hose, if you have vacuum jack the front tires off the ground and manually pull in the actuator and see if the front axle engages, if it does then you have a bad actuator, if it does not you have either a broken/stretched cable or something wrong in the axle such as the shift fork (Highly unlikely)!

If when you check for vacuum at the end of the hose going to the actuator and you have no vacuum then the transfercase vacuum switch is bad, it is located on the side of the T-case and has 3 vacuum lines coming out of it, one of those lines is nothing more than a vent line and it is not uncommon for it to suck some shit into it making it not work anymore.

I highly doubt it is a tccm, 99.99% of the time when 4x4 dont engage it is either the encoder motor, T-case vacuum switch, actuator, 4x4 switch, vacuum hose from switch to actuator, stretched/broken cable...these are all common problems!
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Old August 25th, 2011, 12:48 PM   #6
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If you can hear the encoder motor working and get flashing lights I would check the actuator, I do believe on a 1999 it has a sensor that detects when the actuator is pulled in when trying to engage 4x4, when the signal from that sensor is made you will get a steady light on the 4x4 switch, if it is not made but the encoder has engaged then the light will flash letting you know you have a problem.

The whole system is pretty simple, If you can hear the encoder motor working check that off the list, you replaced the switch so check that off the list. Now move on to the actuator, pull the vacuum hose going to the actuator and have someone shift it into 4x4 and see if it is pulling vacuum at the end of the hose, if you have vacuum jack the front tires off the ground and manually pull in the actuator and see if the front axle engages, if it does then you have a bad actuator, if it does not you have either a broken/stretched cable or something wrong in the axle such as the shift fork (Highly unlikely)!

If when you check for vacuum at the end of the hose going to the actuator and you have no vacuum then the transfercase vacuum switch is bad, it is located on the side of the T-case and has 3 vacuum lines coming out of it, one of those lines is nothing more than a vent line and it is not uncommon for it to suck some shit into it making it not work anymore.

I highly doubt it is a tccm, 99.99% of the time when 4x4 dont engage it is either the encoder motor, T-case vacuum switch, actuator, 4x4 switch, vacuum hose from switch to actuator, stretched/broken cable...these are all common problems!
Thanks for the info! I will jump back into this thing tonight and hopefully get it out of my garage!
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