How to fix Wipers that don’t work Caravan
Don’t you long for the old days when a switch actually controlled the device you wanted to turn on and off? Well, kiss those days goodbye. If you own a Dodge Grand Caravan, or other Chrysler products, and have a problem with the wipers or other similar accessories, you must first understand how these systems work.
First, the switch does NOT connect or disconnect power to the accessory. Its job is to provide a signal to the body control module (BCM), informing it that the driver wants to operate an accessory. Now some of these switches actually connect or disconnect low voltage (usually 5-volts) to the control module. But the wiper switch contains resistors that alter the voltage over 4 or 5 steps going to the controller. Based on the changed voltage, the controller then knows what to do.
So, let’s trace the wiper circuit on this Dodge Caravan.
Power flows to the control coil side of the front wiper ON/OFF relay from a fuse that’s hot all the time. The control coil now has power, but no ground. The front control module (FCM) housed in the Integrated Power Module (IPM) or Totally Integrated Power Module (TIPM—used in later models) is what provides the ground to the ON/OFF relay. What tells the FCM to provide ground? A DIGITAL signal sent over the data bus from the control module to the FCM. So the FCM gets a digital command and grounds the control coil on the ON/OFF relay and to hot electrical contact in the switching portion of the High/Low relay. The High/Low defaults to the low speed when the control coil is NOT energized, so you get low speed operation.
When the driver switches the Multifunction Switch (MFS) to HIGH, the controller sees the request, sends a digital signal to the FCM, and the FCM provides ground to the control coil of the High/Low relay. The contacts move and power is switched to the high speed wire going to the wiper motor.
What goes wrong.
First, check the fuse to the front wiper ON/OFF relay. Next, check the fuse to the accessory relay that powers the FCM. If those are good, remove the ON/OFF relay and jumper across terminals 87A and 30 in the relay socket. That’ll bypass the FCM. You should heat the High/Low relay click and the wipers should operate in low speed. If you don’t get that, jumper across terminals 87A and 30 in the High/Low relay as well. You have now bypassed the wiper switch and ALL other the digital connections. If the wiper motor works, you’ve confirmed the motor and wiring to the motor are good.
Now, turn the wiper switch to LOW and check for ground at terminal 86 in the wiper ON/OFF relay socket. If you get ground, that confirms the FCM is receiving digital data from the controller and is acting properly. If you don’t get ground, the problem can be a faulty FCM, a corroded IPM or TIPM (very common) or a short in the data bus.
Diagnosing the MFS
As I mentioned, the MFS doesn’t switch power to the wiper motor. It receives a voltage from the BCM and runs that voltage through a series of resistors to alter the voltage going back to the BCM. Disconnect the electrical connector to the MFS and connect a DVOM on the OHMS setting to the brown/yellow and violet/blue wires going to the MFS. You should see a different reading for each click on the MFS stalk. A changing reading confirms that the MFS is working, leaving a bad BCM or a short on the data bus. At that point you’ll need some high end diagnostic equipment.
© 2012 Rick MuscoplatPosted on by Rick Muscoplat