* Wiper Control Module (WCM) or related circuitry: This is the most likely culprit. The WCM interprets signals from the wiper switch and sends instructions to the motor. A faulty WCM can cause erratic wiper behavior, including the failure to park correctly. You might find a short or corrosion in the wiring harness going to it.
* Wiper Switch: A malfunctioning wiper switch can send incorrect signals to the WCM. Try testing the switch itself. If possible, swap it with a known good one (from a junkyard car) to see if it resolves the issue.
* Wiring Harness: Check the wiring harness connecting the wiper switch, WCM, and the wiper motor for damage, broken wires, or corrosion. A break in the harness could interfere with proper signal transmission. Pay close attention to the connections at each point.
* Park Switch (if equipped): Some wiper systems use a park switch within the motor mechanism to signal when the wipers are in the park position. If this switch is faulty, it may prevent the wipers from parking correctly. (Less likely since you've replaced the motor, but worth a mention.)
* Incorrect Motor Installation: While less likely given your replacement, double-check that the wiper motor is installed correctly. There might be a slight misalignment affecting the park position.
Troubleshooting Steps:
1. Visual Inspection: Carefully inspect all wiring related to the wiper system, looking for any signs of damage, corrosion, or loose connections.
2. WCM Check (Advanced): This often requires specialized tools or a scan tool to test the WCM and verify it's receiving and sending the correct signals. A mechanic with a diagnostic tool will be necessary.
3. Power/Ground Checks: Use a multimeter to check the power and ground connections to the wiper motor and the WCM.
4. Test the wiper switch: If possible, swap the switch or test its continuity and operation.
5. Wiring Diagram: Consult a wiring diagram for your 1999 Montana. This will help you trace the wiring and identify connections.
Recommendation:
Since the issue persists after replacing the motor, a professional mechanic is recommended. They have the diagnostic tools and expertise to pinpoint the problem, whether it's a faulty WCM, a wiring issue, or a less common problem. Attempting more complex troubleshooting without experience could lead to further damage.
