Have an issue with the speedometer and odometer not working. Tac is working. Had it "scoped" and the computer came up " no trouble". Additionally, the following might be related - the ABS Light stays lite on the panel and the front headlamps remain on all the time so when starting the car it drains the battery partially to start. Any Ideas? The mechanic thinks the ABS module needs to be replaced (rebuilt according to the Blazer forum information) as it might be impacting the odometer / speedometer.

 

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as far as your headlamps go, you might have your drl(daytime running lights) on which is perfectly normal to stay on durring the day and they switch over to the low beams at night. try this to check, hit the parking brake with the vehicle off, then turn the truck on and the lights should be off until you pull the parking break lever.

for your speedometer/abs problem i would start off with the vss(vehicle speed sensor) located on the transmission housing by the tailshaft. it is a two wire sensor. to check, 1.you raise the vehicle in jackstands 2. disconnect the sensor wire harness from the sensor, 3. using aligator clip wires you connect one end of the clips to the probe on the sensor and the other end to a multimeter, you do this for both probes and it doesnt matter what is positive or negative 4. you set the meter to AC voltage. 5. while have the meter visible have some one start the vehicle and put it on drive. the sensor should be producing voltage, the faster the speed of the wheel the higher the voltage. if this is not producing a good signal, replace it if it is good then i would start suspecting an electrical problem which i can help you find with a multimeter

in conclusion i would try a different mechanic, the vss sends a signal to the vcm. then from the vcm to the ipcm and ebcm. so if it is an ebcm(electronic brake conrol module) problem you would be able to have a working speedometer/odometer please let me know if any of this helped