GarageGuideCheck Engine, Oil and Battery Light All On at Once: What It Means and What to Do
When these three lights come on together while you're driving, the cause is usually not three separate problems. Most of the time it's one: the car has stopped charging. A broken or slipped serpentine belt or a failing alternator lets the voltage drop, and the low voltage sets off warning lights all over the dash.
But the oil light can also mean the engine has lost oil pressure, and that can ruin an engine in minutes. So the first thing to do is figure out which situation you’re in.
When to stop driving
If the red oil light stays on while you're moving, pull over as soon as it's safe and shut off the engine. Don't restart it until you've checked the oil. If the temperature gauge climbs toward hot or you see steam, stop: on many engines the serpentine belt also runs the water pump, so a broken belt means the engine will overheat. If the steering suddenly gets heavy, the belt likely broke and took out the power steering, so drive slowly to a safe spot and stop. If the check engine light is flashing, the engine is misfiring badly: reduce speed and get it checked right away. Normal: all three lights come on for a few seconds when you turn the key, before the engine starts. That's the car checking the bulbs. It's only a problem if they stay on once the engine is running.
Most common causes
Broken or slipping serpentine belt
The serpentine belt is the long rubber belt on the front of the engine that turns the alternator, and on many cars the water pump and power steering too. When it breaks or slips off, the alternator stops charging and the battery light comes on. You may hear a loud slap or squeal right before it goes. A broken belt is the most urgent version of this problem because of overheating.
Failing alternator
The alternator charges the battery and powers the car while it runs. When it starts failing, voltage drops, the battery light comes on, and low voltage confuses other systems, including the oil pressure sensor and engine computer. Signs: dim or flickering headlights, a whining noise, a gauge cluster that acts strangely, or a car that dies after running a while.
Loose or corroded battery cables
A bad connection at the battery can cause the same low-voltage symptoms as a bad alternator. This is the cheapest fix of all, so it's worth checking first if the belt is intact.
Actually low oil or oil pressure
Sometimes the oil light is real. If the oil is very low, or the oil pump is failing, the engine isn't getting oil pressure. If the oil light comes on by itself first, or flickers at idle or in turns, low oil is the more likely cause.
After a jump start or with a weak battery
If the battery was just jumped or is near the end of its life, voltage can be low enough to trigger warning lights for a short while after starting. If they go out after a few minutes of driving, the alternator caught up. If they stay on, it didn't.
What you can safely check yourself
- Look at the belt. With the engine off, open the hood and find the serpentine belt at the front or side of the engine. If it's missing, shredded or hanging loose, that's your answer. Don't drive it.
- Check the oil. With the engine off for a few minutes, pull the dipstick, wipe it, push it back in and pull it again. If it's below the lower mark, add the oil listed in your owner's manual.
- Check the battery cables. Look for white or green crust on the terminals and wiggle each clamp. They shouldn't move.
- Test the voltage. With a multimeter on the battery: about 12.4–12.6 volts with the engine off, and about 13.7–14.7 volts with it running. If the running number is around 12.5 or lower, the car isn't charging.
- Get a free test. Most auto parts stores will test your battery and alternator for free, often right in the parking lot.
Step-by-step guides
When to call a mechanic
Call a mechanic or tow if the belt is broken and you're not comfortable replacing it, if the oil light stays on with a full oil level, if the engine overheated, or if the car won't hold a charge after a new battery and a tested-good alternator. A wiring or grounding problem can be hard to track down without the right tools.
Frequently asked questions
Can I keep driving with the check engine, oil and battery lights on?
If the belt is intact, the oil level is fine, and the temperature gauge is normal, the alternator is the likely problem. A car can run on battery power alone for a limited time, often somewhere between 20 minutes and an hour depending on the battery and how much you have turned on. Drive straight to the nearest parts store or shop, and turn off the A/C, radio and anything else you don’t need. At night, headlights drain the battery faster. When the battery runs out, the engine will die wherever you are. If the belt is broken, the oil is low and the light stays on after topping up, or the engine is overheating, have it towed.
Why would a bad alternator turn on the oil light?
When voltage drops, sensors and the engine computer can give false readings. The oil pressure warning is one that often shows up. Still, treat the oil light as real until you've checked the oil level.
Will a new battery fix it?
Only if the battery was the actual problem. If the alternator or belt isn't charging, a new battery will just go dead too, usually within a day. Get the charging system tested first.
How much does it cost to fix?
A serpentine belt is one of the cheaper parts on a car and is often a DIY job. An alternator costs more, and labor varies a lot by vehicle. A free test at a parts store tells you which one you're dealing with before you spend money.
The lights came on, then went off. Is it fixed?
Not necessarily. A slipping belt or a dying alternator can work on and off before failing completely. Check the belt and get a charging test soon.
The lights came on right after I hit a puddle or drove in heavy rain.
Water can make a worn belt slip for a bit. If the lights go away once things dry out, check the belt for wear and the tensioner for weakness. Replace the belt if it's cracked or glazed.
Can I drive with just the check engine light on?
Usually, if it's steady and the car drives normally. That's different from all three lights together. See the Check Engine Light page linked below.
Related problems
Seeing a warning light? See what each dashboard light means.