QuestionMy '96 Chrysler Town & Country mini van has a problem. The speedometer quits and the transmission downshifts to a lower gear. All of the other gages work ok. After a couple of miles the speedometer will come back on and the transmission will shift back into high gear. Also the gear indicator shows all gears with a box around them? What could cause this?
AnswerHi Richard,
I am not familiar with the gear indicator "box around" symbol but perhaps the owner's manual will describe what it means if you have one. The speedo quitting is probably the tell tale reason for the problems. The speedometer is driven by an electrical pulse coming from a distance sendor located on the top of the transaxle housing extension which is the part of the transaxle from which the drive shafts extend outward toward each front wheel. If you look behind the engine and down on the driver's side you will see the driveshaft and the transaxle to which it is attached. On the top of that is an electrical connector to a plate or flange which is the distance sender which is a gear driven by the same gear that drives the axles to turn. So it pulses 8 times for each rotation of the front wheels and thus tell how far and how fast the van is moving. It may be the elctrical connector is loose at the disconnect plug nearby in the wire that runs from it to the engine controller, or the wire has been damaged, or possibly more likely that the gear on the sender was damaged when a mechanic did some work on the right side drive axle (replacement, cv-boot replacement, cv-joint replacement). If the sendor is not removed before pulling the drive axle out of the housing the gear on the sender will be damaged, thus ending the pulsing either intermittantly or permanently, and thus the speedo stops working.
The transmission uses that speed sensor pulsing also in its operation. So that may explain why it shifts down when the speedo stops.
The entire powertrain has some ability to recognize problems and display them as fault codes, two digit numbers, stored in the memory of the engine controller and the transmission controller. You can read out the fault codes stored in the engine controller with your ignition key. Try using the ignition key: turn it "on-off-on-off-on" and leave it "on" (doing this quickly, no longer than 5 seconds). Then watch the 'check engine' light to begin flashing, then pause, flashing, pause, etc. Count the number of flashes before each pause and keep track of the numbers. Repeat the readout and verify the counts are correct. Then group them in pairs in the order that they came out, thus forming two digit numbers. You may notice that the pause is shorter between the digits of a given number, and longer between the numbers themselves. Then send me a 'follow-up' question telling me the results of your readout. By the way, 55 will be the last number (two groups of 5 flashes each) and that is the code for "end of readout". A faulty signal from the sender is a code 15, but it doesn't tell you if the problem is the gear, the wire, or the plug-in. So you will need to inspect those items, and also review whether any mechanical work was done on the right side drive axle lately, which would lead me to suspect the gear is bad. There is a bolt on the top of the sender flange that if you remove it will allow you to examine the gear if you pull the sender up and out of the transaxle housing. The gear us replaceable, with a part from the dealer, you don't have to replace the entire sender.
If fixing that doesn't solve the trans problem then reading the codes stored in its controller is the next step. Unortunately that has to be done with an accessory code reader which might cost $50-90 to buy, or you can have a dealer readout the the codes for about that price. The place to plug in that reader is on the left hand end of the dash, behind a concealed door. Again the codes don't tell you exactly what is wrong but what is causing the problem.
So check over the sender unit, read the engine controller codes, and let me know what you find out.
Roland
