Windshield Wipers

Hi navman54. Welcome to the forum. A real common problem is a bad ground for the motor's mounting plate. While it's turned on and not running, use a grounded test light to check for voltage on the case of the motor. If there is, attach a new ground wire between the plate and the van body. Usually the motor will not run at all in any speed once it comes to a stop, but it's worth checking the ground.

A defective Body Computer is the biggest cause of a dead wiper motor. I never heard of one running slow though. They normally quit completely. Some people have figured out how to add a switch to bypass the computer so the wipers will run constantly at one speed. The delay feature won't work but the washer still works normally. The Body Computer is bolted to the fuse box in front of and above the brake pedal.

The multifunction switch should not cause the motor to run slow because its only job is to signal the setting to the Body Computer. The Body Computer controls the current to the wiper motor. You might also check for any related relays under the hood. I can't remember there being any, but if there are, pitted contacts will cause high resistance and a drop in current to the motor. That can be intermittent. A quick test is to switch a suspect relay with one of the other ones like it.

Caradiodoc

Reply from navman54:

Caradiodoc, thanks for the prompt reply. I checked out both relays in the main power box (under hood), switching out with a new one and also with each other. Result: Nothing positive. With the wiper relay(s) removed (one, or both at same time), nothing on the wipers work. But with the relays in place, the wipers work only on the HI-speed function; but will not park properly nor will the Slow-speed function or the Delay speed function work. However, with either one or both relays removed the windshield "washer" still functions normally. I still haven't had an opportunity to check out the grounding possibility, but have a grandson who's an automotive tech who'll do that for me soon. In any event, is it even likely that the wiper motor could / would work on Hi-speed and nothing else if the ground is bad?

With the BCM being so very expensive, ($600 - $800) do you think it possible that the problem could be in the control switch/turn signal switch on the steering column? Those run around $80 here locally at auto parts stores, whereas it looks like Dodge dealerships are the only places to get the BCM (probably the reason for the outrageous price)? Appreciate any further thoughts you might have on this.
Have a great week. May God bless you, and may God bless America.
Sincerely,
navman54

There are different circuits built into the wiper motor. One circuit stays powered up whenever the ignition switch is on and the wipers are not at their park position. That's the "park" circuit that keeps the motor running after you turn it off so it parks on the bottom of the windshield. The brown wire / white stripe should stay powered up until the wipers park. Unlike the older systems that used a simple park switch inside the wiper motor, the park switch now sends a signal to the Body Computer which keeps the wiper motor relay turned on until the motor parks. Since you swapped relays already, we can rule them out. One test you can do is to turn the ignition switch off, then measure the resistance in the park switch circuit when the wipers are not in the park position. The circuit should read open circuit between the dark green / white wire and ground. When it reads 0 ohms of resistance to ground, that is the signal for the Body Computer to turn off the motor relay. If that switch is shorted, the computer will always think the wipers are in the park position.

On older wiper motors from the early 1990s, it was somewhat common for the park circuit contacts to overheat and when turned off, they would melt into the plastic gear. The next time the wipers were turned on, the rotation of that gear tugged on that stuck contact and bent it up where it would hit the metal cover and short out causing a fuse to blow. This looks like the same motor design but rewired to include the computer in the circuit, so I would suspect similar problems could occur, but instead of blowing a fuse, it would incorrectly tell the computer the wipers are parked all the time.

When the motor runs slow on the low speed setting, measure the voltage on the brown / white wire. If it is less than 12 volts, suspect a pitted relay contact in the high / low speed relay, or a corroded connection in that wire. If you do find 12 volts, but the motor is still running slowly, suspect a problem inside the motor itself. The ground wire circuit can be ruled out since the motor runs normally on high speed.

Caradiodoc

I hope to be 76 someday soon! :) Typically when the Body Computer is the cause of the problem, the wiper motor will be totally dead in all speeds, but when computers are involved, anything can happen. The multifunction switch, (turn signal switch) could cause some speeds to be inoperative but I'd have to think about how to test the circuit because all of the pins are tucked up where you can't reach them. The same voltages should be able to be read at the switch itself instead of trying to access the computer. The clue that leads me to believe the problem is not in the switch is that the motor ran slow before it stopped. The switch doesn't affect the motor speed. It simply tells the computer how often to turn the motor on and on which speed to run it. Running slow could be due to the driver transistor dieing, but it could also be due to a defective motor, poor motor ground, or a pitted relay contact. One relay just turns the motor on. That one has to be good since the motor runs ok at the higher speed. The second relay has one contact for high speed which has to be working, but it has a different contact that is used for the low speed and delay functions. You would have found that by swapping the relays and observing a change in the symptoms.

You're right about the computer controlling a lot of other circuits but each circuit has individual "drivers" which are switching transistors that are either off or on. Any one of them could fail and cause just that one circuit to malfunction.

At least part of the Body Computer has to be working for it to turn on the "Wiper On" relay. That relay must be on to send voltage to the "High / Low" relay. The Computer doesn't control the High / Low relay. That is done strictly with the wiper switch. Since the failures I've run into always involved the motor being dead in all speeds, and this doesn't match your exact symptoms, I suppose it is possible the low speed brush in the wiper motor is bad. The easiest way to tell would be to plug in a different motor and see if it works properly. That would be a lot faster than trying to get the Body Computer out. Be aware that if you try that, you will have to connect an external ground wire temporarily because the motor is normally grounded through the mounting plate.

Caradiodoc