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?

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 1,000 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!
  1. Home
  2. Questions
  3. Headlights dim when revs drop while driving

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: Headlights and dashboard both blink rhythmically when I turn them on 2003 Element

Hello and thank you for contacting YourMechanic. There is a loose ground wire and a short in the ground system with the light switch. Turn the key off and rotate the switch back and forth fast for about 10 times....

Q: Battery terminal corroded

If the battery cable end has considerable white debris on it, then I would replace the entire cable, otherwise the problem will come back. Use a battery post cleaner to make optimal contact surfaces for the cable ends. Also, consider...

Q: How do you operate the fog lights?

If your Fusion is equipped with fog lights, they can provide you with dramatically better visibility when driving in misty or foggy conditions. Of course, you’ll have to know how to turn them on and off to actually enjoy those...

Related articles

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...