Finding that your car won’t turn over but has power must be frustrating. Like the vast majority of drivers, I’ve found myself in that situation on more than one occasion.
Electrical power is pretty much always present in your car – even when it’s ‘off’. The battery still has to power certain appliances, such as the alarm and central locking.
In fact, the only way you’ll ever have no electrical power is if you disconnect the battery or completely discharge it (‘flat’ or ‘dead’).
If your engine won’t turn over, but you have electrical power, don’t panic too much. This is one of the most common problems a mechanic would expect to see.
This guide will walk you through why this is happening and how you can fix it.
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Let me save you a little time with this guide’s key takeaways. I recommend checking the battery and attempting a jump-start (with help if needed).
- Most of the time, the problem lies with the battery.
- Sometimes, the alternator (responsible for charging the battery) or starter motor/solenoid might be breaking.
- It’s also worth checking battery terminals.
- Rarer still (but still possible) are faults with the immobilizer or bad wiring.
- Take your car to a mechanic for any parts replacements.
Car Won’t Start But Has Power: Why?
I’ll do my best to summarize everything I can think of that could lead to your car not starting but having power.
In the end, it all boils down to the starting system. That’s what makes the engine turn over. Therefore, if it won’t, the problem lies somewhere here.
Before jumping into the causes of your car not turning over, let’s consider how your engine starts. This way, I hope to give you all the information you need to figure out the problem yourself.
You should still leave any actual repairs to the professionals. A few things (like jump-starting) can be done at home. But I recommend using a trusted mechanic for almost everything else.
How Does A Modern Car Engine Start?
A car’s engine converts reciprocal movement into rotational force (torque). It does this through a series of connecting rods (con-rods) attached to piston heads at one end and the crankshaft at the other.
Check out this article for more information on how an engine works.
On the end of the crankshaft, you’d find a flywheel. That’s a fancy engineering term for a virtually defect-less circle. It’s designed to handle momentum and torque while maintaining almost perfect balance.
Next to this flywheel is the starter motor. Of course, it’s only needed when you crank your engine to get moving. I’ll go through a quick explanation of how the whole process works.
How An Engine Starts: Step-By-Step
- When you insert the key into the ignition cylinder, the immobilizer system recognizes its signature. It then allows the key to be used for starting your car.
- There are four stages in a standard ignition cylinder: OFF, IGNITION, ON, and START. Turning the key to IGNITION activates the battery system.
- To start your engine, you (no surprise here) twist the key to the START position.
- Electrical current diverts from the battery to the starter motor via the ignition switch. This switch is what the key is technically adjusting. It draws a lot of electrical energy.
- Current powers an electromagnet, attracting the starter solenoid. When this pulls back, the pinion gear juts out. At the same time, it completes a circuit by connecting with two terminals. This allows power to the motor itself, spinning the sticking-out pinion gear.
- This pinion gear meshes with the teeth on the flywheel. It’s much smaller, and the gear ratio is tiny. It can rotate the heavy metal wheel with comparatively little effort.
- As the flywheel and crankshaft rotate, the pistons move up and down. The battery is also driving the electrical fuel pump and spark plugs. After a moment, the engine will start running under its own steam.
- At this point, you let go of the key. Current immediately stops going to the starter solenoid. As a result, the pinion gear retracts, and the motor shuts off. The key will automatically return to the ON position.
In short, that’s how your car’s starting system works. The fault must lie somewhere here if you have electrical power but the engine won’t turn over.
That’s what I’m going to explore on this page.
As a side note, have you ever accidentally twisted the car into its START position with the engine already running? That horrible grinding noise is the pinion gear trying to mesh with the already-spinning flywheel.
Don’t do that!
9 Causes Of Your Car Not Turning Over But Having Power
I’ve ordered these in terms of likelihood based on my experience in the industry.
As I mentioned earlier, I strongly recommend checking your battery first. This is the root problem in around 90% of the cases I worked on.
If it turns out to be something else – well, we can go from there.
Cause #1: 12-Volt Car Battery
When the engine’s running, the alternator provides most of the electrical current needed by the vehicle. However, this, of course, isn’t an option when the engine is off before starting.
The battery is responsible for providing 100% of the electrical current to the starter motor. It’s then ‘topped back up’ (to use simple terms) by the alternator when the car starts and runs.
If the battery is partially discharged, it can’t send enough power to the starter. It doesn’t even have to be completely dead – it will struggle, either way.
As a result, you’ll have electrical power, but your engine won’t turn over.
How To Fix
You’ll likely find that a quick jump-start solves your problem. You probably won’t need to think about it again.
Get some help from a mechanically-minded friend if necessary. Be sure to attach the cables in the correct order and give them long enough to work.
If a jump-start doesn’t work, you might need a new battery. These could be installed by a call-out mechanic. You could also order the part to your house and install it yourself.
I recommend using a mechanic because you sometimes need to reprogram the radio.
Unfortunately, car batteries don’t last forever! They deteriorate over time in the same way as your phone or laptop.
A good car battery brand (Bosch, ACDelco, Optima, Duracell, etc.) will last three to five years. I’ve seen a few last a little longer if the car’s underrun, but they lose efficiency by this point.
I’ve seen cheaper ones last as little as a year before they need replacing.
If you can get your car running, I recommend taking it to a mechanic for a new battery. It’ll cost around the same amount, but they can also do a few other tests. For instance, they’ll check the alternator. If it isn’t charging at its optimal rate, it could be the root problem rather than the battery.
Cause #2: Alternator
I mentioned the alternator in the battery section above.
The alternator’s job is to provide a variable voltage for running the electrical appliances.
It uses the principles of electromagnetism to induce a current in its stator. The rotor spins within it, driven by the auxiliary drive belt. The current then passes through a rectifier (converting it to DC) and a voltage regulator (varying the output.)
When the engine runs, the alternator’s output (controlled by the regulator) is distributed throughout the car. It changes from instant to instant.
Some of this current is diverted to resetting the battery’s chemical imbalance. This ‘recharging’ means it should be ready to power the starter motor next time.
It’s essential to run your car long enough to allow the alternator time to fully recharge the battery. That’s just one of the reasons why regular short journeys are bad for your vehicle’s health.
The battery won’t ‘top up’ when the alternator isn’t charging at maximum efficiency. Thus, it’ll eventually have too little chemical energy to create a current strong enough to power the starter motor.
How To Fix
If your alternator is going bad, you need a new one. This is the cheapest and most likely option for the average daily driver.
It’s best to use a professional mechanic. The alternator is usually relatively easy to install, but it does need to be handled carefully.
This is going to cost somewhere around $600.
It might be somewhat frustrating to know that your alternator is usually fixable.
This isn’t a realistic option for the average driver. You’ll need to pay specialist labor rates for a job that might take a few hours. It ends up being far more expensive than a fast-fit switch-out.
Most regular mechanics don’t have the niche expertise required for this, either.
Of course, if you can afford it and get a reasonable quote from a trusted individual, go for it!
Once the new (or repaired) alternator is installed, check it’s charging properly.
Cause #3: Drive Belt
The serpentine drive belt is the one you can see when you open your hood. It goes by many other names, including ‘drive belt’ and ‘auxiliary belt’.
The drive belt transmits power from the crankshaft to other non-drivetrain components. These include the A/C compressor, power steering pump (if applicable), and – crucially for us – the alternator.
If there’s a problem with the drive belt or its tensioner, the alternator won’t spin fast enough. It won’t generate enough current to charge the battery.
As a result, the car won’t start.
How To Fix
Getting your drive belt replaced is more important than you might think. It’s a simple replacement (around $30 for the part) and could save both your alternator ($600) and battery ($100).
Plus, if you don’t replace it when signs of wear emerge, it might snap while the engine’s running. This could do severe damage to anything under the hood. Don’t let it reach that point!
Cause #4: Battery Terminals & Clamps
Battery terminals are those knobs on the top of the battery. Clamps fix around them, connecting the vehicle circuit to the electrical power source.
Over time, they might work loose, or corrosion might develop. Both of these inhibit the current flow throughout the car’s circuitry.
As a result, you’ll have some electrical power, but not enough to turn the engine over.
How To Fix
Battery clamps are usually simple to fix. Disconnect them from the battery and clean them with a cleaning solution, giving them enough time to dry.
In some cases, you’ll need new ones. I recommend leaving this to the professionals, so you don’t make a severe mistake!
Cleaning the positive and negative terminals is a little riskier. I suggest leaving it to a mechanic. They’re less likely to make dangerous mistakes (such as shorting the battery out).
They’ll grease the terminals up after cleaning them. This is also vital.
Many online blogs will explain how to clean your battery terminals. Most of these aren’t particularly safety conscious (covering your battery in water is a terrible idea), so follow them at your own risk.
Cause #5: Fuses
Fuses are often overlooked. You’ll find a fusebox diagram in your owner’s manual (including where to find the box).
A fuse is designed to blow when too much current passes through it. This protects the circuit from damage that would otherwise be done.
The most likely fuses you’ll want to check out are the ignition switch and starter motor fuses.
How To Fix
You can usually ‘fix’ a blown fuse by replacing it with another one. Ensure you use the correct type and rating and that it’s OEM.
But there’s a little more to it. Something made that fuse blow! For some reason, too much current passed through it.
Before replacing it and forgetting about it, you should investigate why this happened.
This will require some specialist help.
Cause #6: Starter Solenoid Or Motor
The starter solenoid sits on top of the starter motor. It’s designed to pull back (attracted by an electromagnet).
This juts the pinion gear out into place. It also completes the circuit to the motor by connecting two contacts.
In some cars, the solenoid stops working. This isn’t a common issue, but it gets more likely as your vehicle ages past 10 years/100,000 miles.
The most likely causes of a failing starter solenoid are:
- Damaged terminals
- Moisture ingression
- Wear and tear with age
Even if the current still reaches the solenoid, causing the pinion to jut out, there could be a problem with the motor.
If the starter motor itself seizes, it can’t torque the pinion gear.
How To Fix
Take your car to a mechanic and have them inspect it.
If you’re unfamiliar with cars, starter motors can be tricky to find. They’re well hidden, deep beneath the surface components.
No matter the specific issue, the easiest and cheapest thing to do is replace the entire starter motor assembly, including the solenoid.
Including labor, this might come to $200 to $300 (depending on your car).
Cause #7: General Bad Wiring
I haven’t had to work on many cars with flawed or damaged wiring.
The three most likely wiring problems (in my experience) are:
- Loose or corroded connections
- Frayed insulation
- Rodent damage
Loose or corroded connections can happen anywhere. If you have electrical power, but the car won’t start, the first ones to check are those at the starter motor.
Sometimes, they come loose and can even create a short circuit. Watch out for this, as it could be unsafe.
Frayed insulation is another one to look out for. This is often down to aftermarket modifications or, again, a manufacturer oversight. Wires rub against something or get too hot.
Finally, rodent damage is a real problem in some cars. New-ish cars (2000 and later) are some of the worst affected. That’s because the cheap, environmentally friendly soy-based material is very attractive to little nibblers.
For any wire damage, focus on those running between the starter and the battery. Because your car still has power, the battery’s getting current to everything else. This narrows it down quite a lot.
How To Fix
Wire damage isn’t unheard of, but it isn’t the most common problem you’ll ever encounter.
Refrain from attempting this one yourself. Using the right type and gauge of wire is essential. If you install the wrong part or misconnect it, you could cause an electrical fire.
Most mechanics will be able to repair wiring for you. In more complex scenarios, some will use a dedicated electrical engineer. You could save some money by going straight to them in these cases.
You might need to have your car towed to the shop.
Cause #8: Ignition Switch
The ignition switch is also a possible cause of having power but the car won’t turn over.
An ignition switch completes the circuits to the car’s electrical accessories (lights, spark plugs, etc.). When you turn the key to the START position, it also activates the starter motor.
It might not complete the starter motor circuit if it’s broken or broken. The general ignition might still work, though.
The most significant sign of the problem being the ignition switch (or a fuse) is no noise at all when you turn the key. Not even a click or rattle.
How To Fix
Although it’s fundamental to your car’s system, ignition switches don’t usually fail. If your car’s getting on a bit now, it’s more likely.
Take your car to a shop (you’ll need a tow truck) or call a mobile mechanic if you need help getting it started.
If the ignition switch is found to be the problem, they’ll swap it out for a new one. This should immediately fix all your issues.
Expect to pay around $50 for the switch, including programming. You might need an entirely new lock cylinder and housing, which would cost more like $200.
Cause #9: Immobilizer
The immobilizer does precisely what it sounds like. It prevents your car from starting.
How immobilizers work varies from manufacturer to manufacturer and even between models and generations.
Only the designers and trusted partners would really understand the ins and outs. It’s not public knowledge.
This makes perfect sense, of course. Banks don’t design safes and display the schematics for everyone to see.
When an immobilizer goes bad, the ECU doesn’t recognize the transponder signal from the key.
If there’s a problem with the immobilizer, it won’t deactivate. This makes it impossible to start your car. However, electrical power will still reach the appliances.
Modern cars will also display a warning message and/or light on the dashboard.
How To Fix
There’s no way you can fix an immobilizer problem yourself.
Sadly, this is likely to be expensive for the following reasons:
- You need experts in both immobilizers and, specifically, the one fitted to your car.
- It can take some time to find and rectify the fault.
- ECU or similar work is always expensive.
There’s good news in that a failing immobilizer is very rare. In most cars, the system will outlast the vehicle.
I’d suggest immobilizer problems are more likely on older cars.
Car Not Cranking But Has Power: Conclusion
As I’ve demonstrated, there are many possible reasons for this problem.
If your engine won’t even crank but has electrical power, it’s time for a battery test. In most instances, this and a jump-start will fix your issue.
Take your car for a half-hour highway drive to ensure the battery recharges properly.
On the less common occasions that it doesn’t, it’s time for an in-depth analysis of your starting system.
I hope this page will help you pin down your problem!
Remember, if you’re ever unsure, go to a mechanic (or call one out to you). Electrical systems can be dangerous. It’s better to be safe than sorry!