Question about 1999 Chevrolet Silverado 1500

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CompuG my chevy silverado z71 1999 the light of service 4x4 turn on and the 4x4 turn on by itself and got stuck .The transfer case motor,the computer module of 4x4 and the diferential actuator has already been replace and the light is still on. The computer says the ports A and B have problems. Please help the mechanics dont know what to do anymore. HELP!!!!

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Not positive but try cleaning out the sensor connections that run to the transfer case and the front diff. i have a 2004 and those were a problem with mine after cleaning them with electrical spray and tooth brush plug them back in and wrap electical tape around them to help keep moisture and dust out.

Posted on May 16, 2009

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There is a ground that goes to the firewall from the 4w/d computer that goes bad and the computer or the motor can't get the proper voltage/current to do the job they need to do it with. unfortunately some underdash work is required. just rewire the ground and recheck. I am in the process of making a manual system for those but may never see production. I live in NY and we see alot of these cause of salt on the roads.
Good luck -

Posted on Aug 31, 2008

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Circuit Description
The transfer case encoder is a switch that converts a shaft position, representing a mode or range position, into electrical signals for use by the transfer case shift control module. The encoder houses 4 Hall effect sensors that are used for channels P, A, B, and C. These sensors provide a path to ground, when a magnet, (part of the Motor Encoder), passes over them.
The transfer case shift control module supplies an 8 V reference and a ground circuit for the encoder hall effect sensors to function.
The transfer case shift control module supplies current limited 5 V on all the channels, thus as these channels are pulled to ground, the module can interpret the location of the transfer case shift position.
This DTC detects that the transfer case is unable to successfully complete a shift to a requested mode or range.

May 07, 2017 | 2000 Chevrolet Silverado 1500

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Changing the Fluid would help But, It will not solve the Problem. It sounds like you may have a Broken tooth on a Gear inside the Transfer Case. The only real way to fix this is to Take the Transfer Case off and check the Gears and Electronics. Maybe even get it Overhauled.

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