Chrysler Repair: speed sensor, dodge grand caravan, cv joint

Question
HELLO , THIS IS ACTUALLY ONE YEAR BEYOND YOUR RANGE. I HAVE 1996 DODGE GRAND CARAVAN WITH A 3.3 LITRE ENGINE AND APPX. 140,00 MILES ON IT. THE SPEEDOMETER FROM TIME TO TIME GOES CRAZY AND CAUSES THE TRANSMISSON TO DOWN SIFT HARD AT HIGH SPEED OR CAUSES IT NOT TO SHIFT INTO DRIVE. I WAS TOLD BY A FRIEND IT WAS THE SPEED SENSOR BUT I DON'T KNOW WHERE IT'S LOCATED , SOMEONE TOLD ME IT'S BEHIND THE DASH AND OTHERS TOLD ME IT'S ON THE TRANNY. MY QUESTION IS WHERE IS IT AND WOLUD THIS BE THE PROBLEM. THANKS , DAN.

Answer
Hi Daniel,
Thanks for the consideration about my limitations, and fortunately this one is o.k. The sensor is located on the top of the transaxle housing, behind the engine down low at the level of where the half-shafts that drive the front wheels protrude from the housing near the midline of the body. You may see a wire running from a harness at the driver's end of the engine that runs down behind the engine right to it. There will be a disconnect plug in the line. Check that plug to make sure the connection is tight. The most common reason for failure is when a cv-joint is serviced and the mechanic pulls the half-shaft out on the passenger side, if he hasn't taken the trouble to remove the sensor its gear will be damaged in the process. So you can look at the sensor by removing the single bolt that holds it in place on the top of the housing (10mm wrench, I believe), then pull it straight out and examine the gear on the end of it for damage. You may be able to get just the gear from a dealer and replace that. Of course it could also be bad electrically which requires full replacement of the sensor.
To verify that the sensor signal is bad, you can do a check for fault codes stored in the engine controller: go "on-off-on-off-on" with the ignition switch quickly (less than 5 elapsed seconds) then watch the check engine light to begin to flash. If it goes flash, pause, 5 flashes, pause (e.g. the number 15) that means the sensor signal is missing. It will then give two groups of 5 flashes each which is the number 55 for "end of readout".
Well this is more than you want to know, but see what you can find out. Now this is all based on the supposition that the sensor is affecting the transmission, which is possible, but keep in mind that this may not be the cause of the problem. I know the electronic trans keeps track of the engine rpm, but it has its own sensor to detect its output half-shaft rpm. But in any case if you get a code 15 and the speedo is not reflecting what is actually going on with your velocity then you need to deal with that problem and hope the tranny is also fixed.
Roland