Nissan Repair: 1999 Nissan Quest Service Engine Soon Light, vehicle speed sensor, mileage intervals

Question
Hi!
My wife had been driving our 99 Quest on the highway recently when the speedometer started jumping up and down, and then went to zero.
The van seemed to run ok but the check engine soon lamp came on. I took it for a ride shortly thereafter and the speedometer is working again, and it seems to run fine, but the light remains lit.
I disconnected the battery in an attempt to reset the lamp, but that was ineffective.
How do I reset it?
I once owned an 87 Maxima (good car!) that the check engine would come on at periodic mileage intervals and to reset it I would push a reset on a latching relay behind the passenger kick panel.
As the Quest has just over 85K on it I was wondering if it may be a similar situation.
Thank you for whatever information you can provide.
RON


Answer
Ron,

Buy a vehicle speed sensor.  It plugs in where the speedometer cable used to plug in.  This is a square wave generator and that is what tells the computer how fast you are going.  And that is why the speedo does not work and the check engine light came on.  It is a simple change out and then go to Autozone or the like and have the MIL reset for free.