* Low Battery Voltage/Alternator Problem: The most common culprit. When the automatic headlights (and possibly other high-draw components like the blower motor) engage, the increased electrical demand reveals a weak battery or a failing alternator. The system may be drawing more power than the battery can supply, causing the dash lights (which are a lower priority) to dim or turn off. Have your battery and alternator tested at an auto parts store or mechanic.
* Poor Ground Connection: A poor connection to the car's ground (negative battery terminal) can lead to voltage fluctuations. This can cause various electrical components to malfunction, including dimming or failing dash lights when other components draw power.
* Faulty Wiring/Connections: Worn, corroded, or loose connections in the headlight circuit or the dash light circuit can lead to this issue. A short circuit is less likely to cause the lights to simply go off, but rather erratic behavior.
* Faulty Headlight Switch/Relay: Though less likely, a problem within the headlight switch or a related relay could cause unexpected voltage drops affecting other circuits.
* Body Control Module (BCM) Issue: The BCM controls many electrical functions. A malfunction could cause this odd behavior, but this is less probable than the other issues.
Troubleshooting Steps:
1. Battery and Alternator Test: This is the most important first step. Get your battery and alternator tested at an auto parts store. They have free testing equipment.
2. Check Battery Cables: Inspect the battery terminals and cables for corrosion or looseness. Clean them if necessary.
3. Check Fuses: Check the fuses related to the headlights and instrument panel illumination. Consult your owner's manual for the fuse box diagram.
4. Visual Inspection of Wiring: Carefully inspect the wiring harness related to the headlights and dash lights for any visible damage or loose connections. This is difficult without experience and specialized tools.
Recommendation:
Unless you're comfortable working on car electrical systems, it's best to take your Pontiac Vibe to a qualified mechanic. Ignoring this issue could lead to more serious problems, including a complete electrical failure. The testing for the alternator and battery is an easy and inexpensive initial step, but beyond that, a professional diagnosis will pinpoint the problem and prevent further damage.
