The speedometer quit working and it's messing with the transmission.

1991 TOYOTA PREVIA
500,000 MILES
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ALEXLEAHDULLERNORRIS
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After a long haul pulling a car and trailer my speedometer quit working. It seems to be messing up the transmission on highway speeds telling it to shift gears when it shouldn't be. My job relies on this vehicle and would like to attempt to fix it myself if you have any advice. I can't get in to see a mechanic right away and I'm scared I'm going to either break down or get pulled over because I don't know how how fast I'm going!
Sep 6, 2012 at 12:20 AM
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SATURNTECH9
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Do you have a multimeter to do some testing?
Sep 6, 2012 at 12:28 AM
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ALEXLEAHDULLERNORRIS
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No I don't
Sep 6, 2012 at 12:30 AM
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ALEXLEAHDULLERNORRIS
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Do I need one to find out what the problem is? Or is there another way?
Sep 6, 2012 at 12:34 AM
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KHLOW2008
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Get a scan done to check for trouble codes. Most parts stores provides free scanning services.

Most likely the Vehicle Speed Sensor or its circuitry is faulty. Do not jump to conclusion that the sensor is bad. It could be a loose wire or a bad circuit.
Sep 6, 2012 at 11:41 AM
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SATURNTECH9
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Not too sure about obd1 code scanning i know they do obd2 but obd would be a lo harder for them with all the connectors scan tool etc.
Sep 6, 2012 at 4:05 PM
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KHLOW2008
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https://www.2carpros.com/articles/toyota-trouble-code-definitions-and-code-gathering-method-1990-1995

Japanese makes comes with a flash code retrieval for pre-OBD-II models.

Most modern scan tools comes with adapters for code retrieval for these but some are not compatabile as the ECM/PCM are not designed for scan tools as they are like those with sight windows which don't have any scan tool plugs.
Sep 7, 2012 at 4:32 AM
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