Thanks for the dandy information. I would have done the same test, but most people don't have the knowledge to use a separate power supply so I couldn't assume anything.
Both washer motors receive 12 volts from PTC7. That's a 6 amp positive temperature coefficient current limiter. A PTC is a very low resistance semiconductor material up to its current rating. Above that rating, it goes to a near open circuit. When the overload is removed, the resistance goes back down to near 0 ohms. The change occurs almost instantly.
The first step is to check for 12 volts at either motor, dark blue wire, when the ignition switch is turned on. If it's missing, unplug both motors, turn the ignition switch off, and measure the resistance on that circuit to ground. If you find near 0 ohms, one of the wires is grounded. If there's high resistance, suspect a corroded connector pin # 9 at the junction block / body computer. I suppose the PTC could be open too, but I've never heard of one failing. A problem in this circuit would cause both washers to stop working at the same time.
If you do have 12 volts on the dark blue wires, things get pretty straight forward for the front washer. To turn the motor on, the second wire, brown, is grounded by the switch, but the wire goes through the junction block first. This is where the body computer senses the request for the washer and activates the wiper for three swipes. The fact that your wiper runs when pressing the washer button proves the switch is ok.
The rear washer is controlled by the body computer when it gets a signal from the heater / ac controller. All information is sent between the two computers on a single wire. Both of these computers have had an extremely high failure rate. I'm afraid I don't know of any way to diagnose the problem other than just trying new computers. The body computer is very difficult to replace. It is hidden against the firewall in front of the brake pedal. The HVAC controller is real easy to replace, (it is built into the bezel around the radio), but there may be another problem. The unit might have to be calibrated so it knows the position of every vent and temperature door and the characteristics of the AC evaporator temperature sensor. I don't know about '98 models, but for '97, it was extremely frustrating trying to get the "cool down" test to pass, and it won't work if the AC system isn't working properly. When it doesn't pass, the six yellow leds in the switches will flash. That is very annoying. The same recalibrations must be done when the battery is disconnected or run dead.
I think I would worry about the front washer first since it should run without any involvement with computers. Hopefully the problem will also be the cause of the dead rear washer.
Saturday, December 26th, 2009 AT 11:16 PM