speedometer dropped to zero mph from 70 mph but car had not slowed?

2004 BUICK RENDEZVOUS
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ELLENTEA
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Electrical problem
2004 Buick Rendezvous 6 cyl Front Wheel Drive 51,750 miles

Car on interstate road for 150 miles; speedometer dropped to zero mph from 70 mph but car had not slowed. Stopped in store after about 15 minutes. Returned to car, started driving, and speedometer worked OK. Next day speedometer didn't register at all after 60 miles. Following day it registered between 5-15 mph when actual speed was around 60 mph. Later, after 2 hour interval with engine not running, speedometer registered 20-35 mph when actual speed was about 60.
The ODOMETER works fine and accurately. Car has less than 52,000 mileage.
THANK YOU
Oct 20, 2008 at 1:48 PM
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IMPALASS
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Hello Based off of the information you have said, it appears it may be your vehicle speed sensor VSS which is what I would change out first. I have also attached the information about the speedometer. As it states, it takes input from the speed sensor. I have attached information on the sensor, location etc Please check the images below. SPEEDOMETER The instrument panel cluster (IPC) displays the vehicle speed as determined by the engine control module (ECM)/power train control module (PCM). The ECM/PCM converts the data from the vehicle speed sensor to a 4,000 pulses/mile signal. The IPC uses the vehicle speed signal circuit (4,000 pulses/mile ), class 2 message from the ECM/PCM in order to calculate the vehicle speed. If the IPC detects a malfunction in the vehicle speed signal circuit from the ECM/PCM, the IPC uses the class 2 message from the EBCM, indicating the vehicle speed as a backup. If the speedometer reaches (108 mph ) the fuel will shut-off, and it will turn back ON when the speedometer is at (106 mph ). The speedometer displays either miles or kilometers as requested by the activation of the english/metric button on the driver information center (DIC). The associated indicator (km/h or mph) illuminates.


https://images.2carpros.com/forum/automotive_pictures/248015_1_6.jpg

Input Speed Sensor Replacement Removal Procedure Remove the case side cover. Disconnect the transaxle wiring harness.


https://images.2carpros.com/forum/automotive_pictures/248015_2_4.jpg

Remove the input speed sensor clip (441) from the case cover. Remove the input speed sensor (440) from the case cover.


https://images.2carpros.com/forum/automotive_pictures/248015_3_2.jpg

Inspect the input speed sensor (440) for the following conditions: Damaged or missing magnet Damaged housing Bent or missing electrical terminals Damaged speed sensor clip (441) Installation Procedure


https://images.2carpros.com/forum/automotive_pictures/248015_4_2.jpg

Install the input speed sensor (440) into the case cover. Install the input speed sensor clip (441) into the case cover. Connect the transaxle wiring harness. Install the case side cover. Check out the images (Below). Please let us know what happens.
Images (Click to enlarge)
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Oct 20, 2008 at 5:48 PM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.