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Transtech, transmission expert
Category: Car
Satisfied Customers: 2
Experience:  transmission shop owner for 11 years
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93 gmc: wheel drive..comeing..transfer case..speedometer

Customer Question

i have a 93 gmc sierraXXXXXcan not get to shift took to mechanic said it was not the trans he said that the spedometer was not working and would not let the trans shift he first told me computer that did not work so he told me to change the wire that was about 18 inches long comeing off the transfer case i did still can't get speedometer to work was wondering if any one had a suggestion
Submitted: 7 years ago.
Category: Car
Expert:  Transtech replied 7 years ago.
the ecm does need a signal from the speed sensor to comand the trans to shift. did you try replacing the speed sensor first? if so the next step would be to do a resistance check on the speed sensor circuit. check the resistance of the new speed sensor first than check the circuit on the two wires at the ecm. the reading should be the same or very close. this will verify the wiring from the ecm to the sensor. if it is not the same than trace the wires along the frame and look for a bad spot. usualy the wire will be corroded. also note some models had another module called a drac module inbetween the speed sensor and the ecm. if the drac fails and does not send the speed signal to the rest of the components the trans will not shift and other problems such as no speedometer or cruise control. if ecm is new and speed sensor circuit checks ok than suppect drac. hope this helps. let me know.
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Customer: replied 7 years ago.
where is the speed sensor
Customer: replied 7 years ago.

where is the speed sensor

and how do i do a resistance check

Expert:  Transtech replied 7 years ago.
the speed sensor is on the rear of the transfer case where the driveshaft connects. you need a multimeter (volt-ohm meter) to do a resistance test. set the meter to ohms, and auto range or 0 to 100 on the scale. If the speed sensor has not been replaced i would try that first because the fail quit often and they are not expensive. You can get one at any parts store.
Customer: replied 7 years ago.

did u get your money do not know how this works


Expert:  Transtech replied 7 years ago.
yes, thank you
Customer: replied 7 years ago.
sorry one more question how do u check speed sensor truck running plug hooked up how does the prongs on meter get to it or whatever
Expert:  Transtech replied 7 years ago.
a resistance check is always done with the power removed from the circuit. if there is power on the circuit it will blow the fuse in the meter. turn truck off, unplug the wire connector from the sensor and touch one leed of the meter to one terminal in the sensor, the other lead to the second terminal. the resistance should be 370 ohms to 440 ohms.