Car Won’t Start After Replacing Serpentine Belt: Uncovered!

You’ve just replaced the serpentine belt in your car, but now it won’t start. You’re frustrated and wondering what could be causing this issue.

This problem can be caused by a variety of factors, including a misaligned belt, damaged pulleys, or a dead battery. 

In this article, we’ll explore the possible reasons why your car won’t start after replacing the serpentine belt and provide you with some practical solutions.

So, why car won’t start after replacing the serpentine belt? The most common cause could be that the components like the alternator, water pump, and idler pulley could be lockup that are preventing the serpentine from turning over. Everything except the crankshaft pulley, over which the serpentine belt flows, should rotate freely If the alternator is locked up, the new serpentine belt will grip the seized alternator so well that it won’t even crank over. Furthermore, if your battery is dead or weak, your car may not have enough power to start even if the serpentine belt is functioning properly. Lastly, you also need to check the battery connection to the starter terminal. If you don’t even hear a cranking sound, either a starter motor or a battery could be bad.

Note: Normally, during the serpentine belt replacement process, we have to disconnect the negative terminal of the battery to avoid a short circuit. So, after the installation of the serpentine belt, make sure you have properly tightened the negative terminal of the battery.

Bonus Read: My car sometimes start and sometimes it doesn’t

What Causes Serpentine Belt To Break Or Get Snapped?

I have come across several instances where the serpentine belt has broken or snapped. This belt is a crucial component for your car’s engine as it helps power several auxiliary systems, including the alternator, power steering pump, and air conditioning compressor.

Here are some of the main reasons why a serpentine belt may break or snap:

1. Something Locked Up Under the Hood

One of the most common reasons for a serpentine belt to break or snap is when something locks up under the hood. This could be due to a seized pulley, a frozen alternator, or a malfunctioning air conditioning compressor. When any of these parts lock up, they cause the belt to overwork and snap. Lastly, a faulty water pump can cause the serpentine belt to snap due to the drag created by the impeller. 

2. Extreme temperatures

Another cause of serpentine belt failure is exposure to extreme temperatures. High temperatures can cause the rubber material of the belt to expand and contract, resulting in cracks or tears. Low temperatures can make the rubber material stiff and brittle, increasing the risk of snapping.

3. Wear and tear

Another common reason for a snapped serpentine belt is wear and tear. Over time, the belt can become worn out due to constant use, exposure to heat and cold, and contamination from oil and dirt. As the belt ages, it can develop cracks, splits, and frays that weaken its structure and eventually lead to failure.

4. Foreign objects

Another cause of serpentine belt failure is foreign objects getting caught in the belt or the pulleys. This can happen due to road debris, dirt, dust, leaves, or other items that may enter the engine bay through the grille or other openings. Foreign objects can damage the belt or the pulleys by cutting, scratching, or jamming them.

5. Oil or coolant leaks

Another cause of serpentine belt failure is oil or coolant leaks from the engine or its accessories. Oil or coolant can contaminate the belt and make it slippery, causing it to lose traction on the pulleys or slip off entirely. Oil or coolant can also degrade the rubber material of the belt and make it brittle or swollen. You can read my guide on oil leaks and coolant leaks to learn more.

Causes of Car Not Starting After Replacing Serpentine Belt 

1. Battery Is Drained or Damaged

When the serpentine belt breaks or becomes loose, it can prevent the alternator from spinning, which means that the alternator can’t charge the battery. This can cause the car’s electrical system to rely solely on the battery, which can drain the battery’s power quickly.

If the battery is drained, the car may not have enough power to start the engine. On the other hand, if the battery is damaged, it may not be able to hold a charge even if it’s fully charged. This can also cause the car to stall or not start after replacing the serpentine belt.

How can you tell if the battery is drained or damaged? 

checking battery voltage

To check if the battery is drained, you can use a voltmeter to measure the voltage of the battery without cranking the engine. A fully charged battery should have a voltage reading of around 12.6 volts.

If you are trying to crank the engine, the battery voltage at that point should not drop below 9.5V. If the voltage reading is significantly lower than this, it means that the battery is drained. 

What should you do if the battery is drained or damaged?

If the battery is drained, you may be able to jumpstart the car using jumper cables and another vehicle’s battery. Make sure to follow the proper jumpstarting procedure to avoid damaging your car’s electrical system. If the battery is still not charged enough, it means the battery is damaged, you have to replace your car battery.

2. Alternator Is Seized

checking seized alternator

A car’s alternator is responsible for providing electrical power to the battery while the car is running, and it’s driven by the serpentine belt. 

If the alternator seizes up, it can cause the serpentine belt to break or come off, which will cause the car to stop running. Even after replacing the serpentine belt, the car may not start because the alternator is still seized up and unable to provide power to the car’s electrical system.

This is because the battery, which is responsible for providing power to start the car, needs to be recharged by the alternator. If the alternator is seized up, it won’t be able to recharge the battery, and the car won’t start.

How does an alternator become seized?

Alternator becomes seized in the following ways:

  • Lack of maintenance: One of the most common causes of a seized engine alternator is a lack of maintenance. Over time, the alternator can become clogged with dirt, dust, and debris, which can cause it to overheat and become damaged.
  • Worn-out bearings: The alternator has two bearings that support the shaft and allow it to spin freely. These bearings are lubricated by grease or oil and can wear out over time due to normal use or lack of maintenance. When the bearings fail, they can create noise, vibration, heat, or friction that can seize the alternator.
  • Rust in the alternator: Rust can also develop in the alternator due to clearance between the stator and rotor of the alternator. It will also seize the alternator. 

So, when worn or seized the overrunning alternator pulley does not disengage correctly, it generates an up-and-down snatching motion on the serpentine belt.

If your car won’t start after replacing the serpentine belt, the first thing you should do is remove the serpentine belt and try to turn the alternator pulley by hand. If the alternator is seized up, it won’t turn at all, or it will be very difficult to turn. 

To fix a seized alternator, you should put a breaker bar on the nut of the alternator pulley, and try to force it to turn, forward and backward. You can also spray a wicking coil into the winding of the alternator from the pulley side to fix a seized alternator.

3. Starter Motor Is Fried Up

Bad starter motor

If your engine is not even cranking over and you have checked that your car battery is fine, the chances are that the starter or its connections have gone bad. You could have mistakenly removed the wire from the starter while replacing the serpentine belt which would cause failure in starting of your car.

A starter is an electric motor that turns the engine over to start the car. It’s located on the engine block and is connected to the battery and ignition switch. 

When you turn the ignition key, the battery sends a small amount of current to the starter solenoid, which activates a magnetic coil and pushes a plunger forward. This plunger closes a pair of contacts that allow a large amount of current to flow from the battery to the starter motor.

The starter motor then spins the flywheel, which turns the crankshaft and moves the pistons. This creates compression in the cylinders and allows the spark plugs to ignite the fuel-air mixture. The engine then starts running and powers the car.

How does a starter become bad?

A starter can get damaged by various factors, such as:

  • Loose or dirty connections: If the wires or terminals that connect the battery, the solenoid, and the starter motor are loose or corroded, they can prevent enough current from reaching the starter. This can cause intermittent or no-start problems. To learn more about starter connections, you can read my guide on where wires go on the starter.
  • Worn-out or broken parts: Over time, the parts inside the starter can wear out or break due to friction, heat, or stress. For example, the brushes that transfer electricity to the rotating armature of the starter motor can wear out and lose contact. The gears that mesh with the flywheel can also get stripped or dislodged. The solenoid plunger or contacts can also get stuck or burned out. Any of these issues can prevent the starter from spinning or engaging with the flywheel.
  • Oil leaks: If oil leaks from the engine or other components onto the starter, it can damage its electrical components or cause short circuits. Oil can also attract dirt and dust that can clog or corrode the connections.

If all connections of the starter are fine, you should try hitting the starter with the hammer, and see if your car starts on not.

4. Air Intake Hose and Vacuum Hoses Have Come Loose

During the serpentine belt replacement process, we may have to remove the air intake hose and other vacuum hoses to access the serpentine belt, depending on the make and model of the vehicle.

Sometimes, the hoses may not have been installed properly in the first place. If the clamps that hold the hoses in place are not tightened properly, the hoses can come loose over time, leading to the issues you are experiencing. 

Loose hoses can create air leaks that disrupt the proper ratio of air and fuel in the engine. This can make the engine run too lean, which will cause your car to crank but not start.

 The air intake hose is usually shaped like a tube or a funnel, and it may have clamps or connectors to secure it in place. The vacuum hoses are small rubber hoses that connect various components of the engine, such as the intake manifold, the fuel pressure regulator, the PCV valve, and the EGR valve.

5. Serpentine Belt Is Not Installed Properly

If the serpentine belt is not installed correctly, it can cause the engine to not start. If the serpentine belt after installation is either too tight or too loose, it has either the wrong size or it is not installed properly.

While installing the new serpentine belt, you should follow these tips:

  • Compare the old belt with the new one and make sure they are the same size and type. Also, inspect the pulleys and the tensioner for any signs of wear or damage and replace them if needed.
  • Install the new belt by following the diagram in your maintenance manual and routing it around the pulleys. If the serpentine belt is not threaded through the pulleys in the correct order, it will cause the serpentine belt to slip, stretch or break.
  • Make sure the belt is seated properly on each pulley and not twisted or misaligned.

6. Loose Wires of the Sensors

While removing the serpentine belt, you might have to tackle with the connections of MAF/MAP sensor, crankshaft position sensor (CKP) and engine coolant temperature (ECT) sensors. Make sure that these sensors have secured connections, and you have not contaminated them. 

You should specially check the CKP sensor as it is responsible for the proper ignition timing of the engine. If CKP sensor is not working, the ECU couldn’t determine the exact ignition timing. As a result, the car won’t start. You can read my guide on car won’t start after replacing CKP sensor.

Final Thoughts

In summary, replacing a serpentine belt can be tricky, with many potential issues that could prevent your car from starting afterward.

Carefully check battery connections, inspect the alternator and starter for damage, verify all sensors are plugged in, and ensure no hoses came loose during the repair.

Also, confirm the new belt is correctly routed and properly tensioned. With patience and methodical troubleshooting, you can identify the root cause and get your car running smoothly again after a serpentine belt replacement.

Proper installation is key, along with meticulously confirming all connections are secure post-repair.

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