1. Fuses: The power mirrors likely have their own fuse in the fuse box, usually located under the hood or inside the vehicle (check your owner's manual for the exact location). Check for a blown fuse; replace it with one of the same amperage rating if necessary.
2. Power Mirror Switch: The switch itself could be faulty. Try using a different mirror control to see if that works. If one works and the other doesn't, the problem likely lies with the switch itself or the wiring to the malfunctioning mirror.
3. Wiring: Look for broken, loose, or corroded wires in the wiring harness leading to the mirrors. This is especially true at the points where the wires enter the door. Check for damage in the rubber boot that protects the wiring as it enters the door. You might need a wiring diagram to trace the circuits.
4. Motor: The motor in one or both of the mirrors might have failed. This is less likely if both mirrors are malfunctioning, but is possible if just one is broken. Testing the motor requires some electrical knowledge and multimeter.
5. Relay (Less Likely): Some vehicles use a relay to control the power mirrors. A faulty relay could be the culprit, but this is less common. You'd need to locate the relay (if present) in the fuse box and test it (may require a multimeter).
6. Ground Connection: A poor ground connection can prevent the mirrors from working. Check the ground points associated with the mirror circuits.
7. BCM (Body Control Module): In some cases, a problem with the Body Control Module can affect power mirror operation. This is a more complex issue and would usually require a diagnostic scan tool to determine if the BCM is at fault.
Troubleshooting Steps:
1. Start with the fuses. This is the easiest and cheapest check.
2. Inspect the wiring. Look for obvious damage. This is often the culprit.
3. Test the switch. See if one mirror switch works better than the other.
4. If only one mirror is out, the problem is likely with that specific mirror's motor or wiring.
5. If you're comfortable with basic electrical work and have a multimeter, you can test the voltage at the motor and the switch to narrow down the problem.
If you are not comfortable working with car electronics or cannot locate and diagnose the issue, it is best to take your Blazer to a qualified mechanic. They will have the tools and expertise to properly diagnose and repair the problem.
