Chrysler Repair: 2002 T & C Van knocking/bucking when low speed, speedometer needle, needle races

Question
"my 2002 T & C has a bucking as applying gas around 25-35 and 40-45 when it knocks the speedometer needle goes crazy.  Yesterday my speedo,quit. Today it's working again but it still bucks and the needle races.  I can be driving with cruise and it runs fine but looking at the speedo..it shows the car not going the speed it's going."


Answer
Hi Diane,
The speedometer is electrically driven from a sensor located at the far end of the transmission called the 'output speed sensor'. That signal is also used to control the shifting of the transmission. So that sensor may be the cause of part of this. It costs about $75, and the job takes about 15 minutes. But there may be other reasons for the bucking(possibly you are experiencing misfiring or a "miss").
The most efficient approach is to get a readout of both the engine and transmission control modules which can self-detect most problems, including this sensor if it is indeed at fault, and log them in their memories as 4-digit fault codes. A readout of fault codes from the memories can be had for free at most Autozone parts stores, of for about $40 at an independent shop. There is a jack under the dash by the steering column into which the reader is plugged to get the fault codes. If you do this, get the fault code numbers, and ask what they mean, what they recommend doing, and how much it will cost. Then write back and tell me what you have learned and we will go from there. Please mention the engine size (L) when doing so.
Roland