# Speed Sensor? Tranny?



## Guest (May 23, 2003)

I borrowed my mother-in-law's 2000 Sentra GXE this week. It only has 59,900 miles on it. When leaving a stoplight the other morning, the rpms revved freely, like the automatic transmission was slipping. I let the revs come back down. Tried again. No problem. I drove my 60 mile commute with no problem. On the way home, at a steady speed on the interstate, the rpms would inexplicably fluctuate about 500rpm. The "check engine" light also turned on. The car freely revved one other time after I got off the interstate. I went by the local Nissan dealer to have it checked out. They put it on the diagnostic machine ($50). They said that it is a faulty vehicle speed sensor. When I left the dealer to go home, the car was doing something it hadn't done before. It would pull fairly strong through the rpm range, but then, it would freely rev until ~6500rpm and about 30-35mph, at that point it would begin pulling again. I had to drive all the way home by getting up to 30mph and letting off the gas until the car slowed down almost to a stop, then repeat. What in the world is going on with this car? Mother-in-law is coming home this weekend. I don't want to be the one who broke her car! I need any help that I can get in figuring this out quickly.
Thanks,
Marcus


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## sr20dem0n (Mar 19, 2003)

Damn, if it was a manual I would say that the clutch was gone, but then again it isn't a manual...lol. If the dealer says it's a faulty speed sensor then why don't you replace the speed sensor? Sounds like a good enough bet to me, but I've never heard of such a sensor or of an auto tranny doing that before.


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## Guest (May 23, 2003)

I don't like replacing something unless I'm sure that it's the source of the problem. Especially when the part runs $120, they charged $50 for the diagnostic, and want $80 for the labor. I'm a poor grad student with a baby on the way. I usually do all my own work. A friend who works at a junkyard is trying to dig a vehicle speed sensor up for me. Autozone can't even get one. I don't know much about nissans. I usually work on old ford and chevy v8s, VWs and Cadillac northstars. I've done some checking on what the speed sensor does and it seems like it might be the source. What I've found so far seems to indicate that the Speed sensor works in conjunction with the ecu to mesh the functions of the engine and transmission. It apparently helps to tell the transmission when to shift. I just don't understand why it went from driving a 120 mile round trip to failure within seconds of leaving the dealer.


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## Guest (May 23, 2003)

To get a good look at the VSS you need an oscilloscope to monitor the pulses. I think that you are correct when you say that the VSS contributes to shift patterns of the transmission. If you are getting the code for the VSS... you should certainly check the connectors involved between the VSS and ECU first before and replacement is planned of the sensor itself...


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## germex (Jan 15, 2003)

This may seem like a really stupid question, but sometimes the most obvious things are overlooked. Did you check the tranny for leaks and to make sure the fluid was at the proper level? Call a tranny shop and ask them what they think. I have a problem with dealers diagnostics, they usually rely on computers to tell them what's wrong. Sometimes the computer reads wrong or doesn't show a problem when there actually is one. It also may be something as simple as needing the bands adjusted. With 60,000 miles on the car that may be a good thing to check. Let us know what you find out.


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