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Dave Nova
Dave Nova, GMC Technician
Category: GM
Satisfied Customers: 19451
Experience:  ASE Master Certification. GM World Class Certification
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98 GMC SAVANA 2500: V6 4.3L VAN..40 mph..IT MY BE THE SPEED SENSOR

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I HAVE A 98 GMC SAVANA 2500 V6 4.3L VAN, THE PROBLEM IS MY SPEEDOMETER NEDDLE GOES UP TO 100 MPH WHEN IM DOING 40 MPH, AND AT THAT TIME THE TRUCK BUCKLES AND WONT TAKE GAS EVEN IF I FLOOR THE PEDDLE, I WAS THINKING IT MY BE THE SPEED SENSOR OR THE CRANKSHAFT SENSOR BUT IM NOT SURE, CAN YOU HELP
Does the speedometer register 0 when stopped?
Customer: replied 7 years ago.
yes it say's 0

Does the speed seem to work okay most of the time, then just jump to a higher speed, or is the speed always registering faster than you are going?

Customer: replied 7 years ago.
ok the speedometer when starting to move, say's im doing 10 mph when i know im only just coming off the brakes and im only doing about5mph also i had this problem all day but by the evening hours the truck ran fine no problems the speedometer worked fine and the truck didnt buckle and 40mph was doing 70mph and the speedometer and everything work normal.now this morning its back to the same problem
The speed signal comes from the VSS (vehicle speed sensor) to the ECM (engine control module). Obviously the ECM is seeing speeds that are too hight as well, since it is cutting off fuel at 100 mph. My suggestion is to replace the VSS on the transmission.
Customer: replied 7 years ago.
the vss is the sensor located on the passenger side of the trans very close to the drive shaft with 2 wires

Should be on drivers side of the transmission, with 2 wires and near to the driveshaft.

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