Skip the auto shop - Our mechanics make house calls

Q: Headlights dim when revs drop while driving

asked by on

The zap in Corolla. Whenever the revs drop during driving, coasting for example, the headlights dim to the parking light level. Should I have a battery replacement? I'm planning to do that. Is there something else to look into?

A: Check the battery and have the alternator l...

Check the battery and have the alternator load tested. A lot of times it is as simple as you needing a new battery or an alternator. You can get the car load tested or try or test the alternator yourself. They will tell you which one it is. A lot of times, it is more of a bad alternator than a battery because the alternator runs when the car starts. Unless your battery is really bad, then it is usually the bad alternator. If the battery is bad, it wouldn’t start at all. If you need help having this problem resolved, a certified mechanic, such as one from YourMechanic, can check your headlight issue to verify what the actual problem is.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Sluggish start. Bad starter or bad battery? Female. Don't want to get taken by shop.

Hi! That "sluggish starting" (slow cranking speed) is the most common symptom when a battery is at the end of its life. The age of your car is also just about in the normal range for how long batteries last....

Q: How to use Napa 85-200 12V. 1 Amp. This battery charger is slow.

Hi there. When you get a Napa 85-200 12 volt 1 amp battery charger, first you will need to check the battery for the water level. This is done by removing the caps to the battery. (Warning: Do not remove...

Q: Lights won't turn off

This is an issue with the electronic system, which is controlled by computers such as a (BCM) body control module. The correct voltages and inputs have to be in order or issues like this can happen. The first step is...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...